

SDCC Compiler User Guide

SDCC [Input: sdcc_version]
$Date:: 2023-05-30 #$ 
$Revision: 14093 $



Table of Contents

Chapter 1 Introduction
1.1 About SDCC
1.2 SDCC Suite Licenses
1.3 Documentation
1.4 Typographic conventions
1.5 Compatibility with previous versions
1.6 System Requirements
1.7 Other Resources
Chapter 2 Installing SDCC
2.1 Configure Options
2.2 Install paths
2.3 Search Paths
2.4 Building SDCC
2.4.1 Building SDCC on Linux
2.4.2 Building SDCC on Mac OS X
2.4.3 Cross compiling SDCC on Linux for Windows
2.4.4 Building SDCC using Cygwin and Mingw32
2.4.5 Building SDCC Using Microsoft Visual C++ 2010 (MSVC)
2.4.6 Windows Install Using a ZIP Package
2.4.7 Windows Install Using the Setup Program
2.4.8 VPATH feature
2.5 Building the Documentation
2.6 Reading the Documentation
2.7 Testing the SDCC Compiler
2.8 Install Trouble-shooting
2.8.1 If SDCC does not build correctly
2.8.2 What the ”./configure” does
2.8.3 What the ”make” does
2.8.4 What the ”make install” command does.
2.9 Components of SDCC
2.9.1 sdcc - The Compiler
2.9.2 sdcpp - The C-Preprocessor
2.9.3 sdas, sdld - The Assemblers and Linkage Editors
2.9.4 s51, sz80, shc08, sstm8 - The Simulators
2.9.5 sdcdb - Source Level Debugger
Chapter 3 Using SDCC
3.1 Standard-Compliance
3.1.1 ISO C90 and ANSI C89
3.1.2 ISO C95
3.1.3 ISO C99
3.1.4 ISO C11 and ISO C17
3.1.5 ISO C2X
3.1.6 Embedded C
3.1.7 Implementation-defined behavior
3.1.7.1 Translation
3.1.7.2 Environment
3.1.7.3 Identifiers
3.1.7.4 Characters
3.1.7.5 Integers
3.1.7.6 Floating point
3.1.7.7 Arrays and Pointers
3.1.7.8 Hints
3.1.7.9 Structures, unions, enumerations and bit-fields
3.1.7.10 Qualifiers
3.1.7.11 Preprocessing directives
3.1.7.12 Library functions
3.1.7.13 Architecture
3.2 Compiling
3.2.1 Single Source File Projects
3.2.2 Postprocessing the Intel Hex file
3.2.3 Projects with Multiple Source Files
3.2.4 Projects with Additional Libraries
3.2.5 Using sdar to Create and Manage Libraries
3.3 Command Line Options
3.3.1 Processor Selection Options
3.3.2 Preprocessor Options
3.3.3 Optimization Options
3.3.4 Other Options
3.3.5 Linker Options
3.3.6 MCS51 Options
3.3.7 DS390 / DS400 Options
3.3.8 Options common to all z80-related ports (z80, z180, r2k, r3ka, sm83, tlcs90, ez80_z80)
3.3.9 Z80 Options (apply to z80, z180, r2k, r3ka, tlcs90, ez80_z80)
3.3.10 SM83 Options
3.3.11 STM8 Options
3.3.12 Intermediate Dump Options
3.3.13 Redirecting output on Windows Shells
3.4 Environment variables
3.5 SDCC Language Extensions
3.5.1 MCS51/DS390 intrinsic named address spaces
3.5.1.1 __data / __near
3.5.1.2 __xdata / __far
3.5.1.3 __idata
3.5.1.4 __pdata
3.5.1.5 __code
3.5.1.6 __bit
3.5.1.7 __sfr / __sfr16 / __sfr32 / __sbit
3.5.1.8 Pointers to MCS51/DS390 intrinsic named address spaces
3.5.1.9 Notes on MCS51 memory layout
3.5.2 Z80/Z180/eZ80 intrinsic named address spaces
3.5.2.1 __sfr (in/out to 8-bit addresses)
3.5.2.2 __banked __sfr (in/out to 16-bit addresses)
3.5.2.3 __sfr (in0/out0 to 8 bit addresses on Z180/HD64180)
3.5.3 SM83 intrinsic named address spaces
3.5.3.1 __sfr
3.5.4 HC08/S08 intrinsic named address spaces
3.5.4.1 __data 
3.5.4.2 __xdata 
3.5.5 PDK14/PDK15 intrinsic named address spaces
3.5.5.1 __sfr
3.5.5.2 __sfr16
3.5.6 Non-intrinsic named address spaces
3.5.7 Absolute Addressing
3.5.8 __sdcc_external_startup
3.5.9 Preserved register specification
3.5.10 Binary constants
3.5.11 Returning void
3.5.12 Omitting promotion on arguments of vararg function (does not apply to pdk13, pdk14, pdk15)
3.6 Parameters and Local Variables
3.7 Overlaying
3.8 Interrupt Service Routines
3.8.1 General Information
3.8.1.1 Common interrupt pitfall: variable not declared volatile
3.8.1.2 Common interrupt pitfall: non-atomic access
3.8.1.3 Common interrupt pitfall: stack overflow
3.8.1.4 Common interrupt pitfall: use of non-reentrant functions
3.8.2 MCS51/DS390 Interrupt Service Routines
3.8.3 HC08 Interrupt Service Routines
3.8.4 Z80, Z180 and eZ80 Interrupt Service Routines
3.8.5 Rabbit 2000, 3000 and 3000A Interrupt Service Routines
3.8.6 SM83 and TLCS-90 Interrupt Service Routines
3.8.7 STM8 Interrupt Service Routines
3.9 Enabling and Disabling Interrupts
3.9.1 Critical Functions and Critical Statements
3.9.2 Enabling and Disabling Interrupts directly
3.9.3 Semaphore locking (mcs51/ds390)
3.10 Functions using private register banks (mcs51/ds390)
3.11 Inline Assembler Code
3.11.1 Inline Assembler Code Formats
3.11.1.1 Old __asm ... __endasm; Format
3.11.1.2 New __asm__ (”inline_assembler_code”) Format
3.11.2 A Step by Step Introduction
3.11.3 Naked Functions
3.11.4 Use of Labels within Inline Assembler
3.12 Support routines for integer multiplicative operators
3.13 Floating Point Support
3.14 Library Routines
3.14.1 Compiler support routines (_gptrget, _mulint etc.)
3.14.2 Stdclib functions (puts, printf, strcat etc.)
3.14.2.1 <stdio.h>
getchar(), putchar()
printf()
3.14.2.2 <malloc.h>
3.14.3 Math functions (sinf, powf, sqrtf etc.)
3.14.3.1 <math.h>
3.14.4 Other libraries
3.15 Memory Models
3.15.1 MCS51 Memory Models
3.15.1.1 Small, Medium, Large and Huge
3.15.1.2 External Stack
3.15.2 DS390 Memory Model
3.15.3 STM8 Memory Models
3.16 Pragmas
3.17 Defines Created by the Compiler
Chapter 4 Notes on supported Processors
4.1 MCS51 variants
4.1.1 pdata access by SFR
4.1.2 Other Features available by SFR
4.1.3 Bankswitching
4.1.3.1 Hardware
4.1.3.2 Software
4.1.4 MCS51/DS390 Startup Code
4.1.5 Interfacing with Assembler Code
4.1.5.1 Global Registers used for Parameter Passing
4.1.5.2 Register usage
4.1.5.3 Assembler Routine (non-reentrant)
4.1.5.4 Assembler Routine (reentrant)
4.2 DS400 port
4.3 The Z80, Z180, Rabbit 2000, Rabbit 2000A, Rabbit 3000A, SM83 (GameBoy), eZ80 and TLCS-90 ports
4.3.1 Startup Code
4.3.2 Rabbit ports
4.3.2.1 Rabbit wait states
4.3.3 Z80, Z180 and Z80N calling conventions
4.3.3.1 Z80 SDCC calling convention, version 1
4.3.3.2 Z80 SDCC calling convention, version 0
4.3.4 Rabbit 2000, Rabbit 2000A, Rabbit 3000A, eZ80 and TLCS-90 calling conventions
4.3.4.1 Rabbit SDCC calling convention, version 1
4.3.5 SM83 calling conventions
4.3.5.1 SM83 SDCC calling convention, version 1
4.3.5.2 SM83 SDCC calling convention, version 0
4.3.6 Small-C calling convention
4.3.7 Complex instructions
4.3.8 Unsafe reads
4.3.9 Z80 banked calls
4.4 The HC08 and S08 ports
4.4.1 Startup Code
4.5 The STM8 port
4.5.1 Calling conventions
4.5.1.1 SDCC calling convention, version 1
4.5.1.2 SDCC calling convention, version 0
4.5.1.3 Raisonance calling convention
4.5.1.4 IAR calling convention
4.5.1.5 Cosmic calling convention
4.6 The PIC14 port
4.6.1 PIC Code Pages and Memory Banks
4.6.2 Adding New Devices to the Port 
4.6.3 Interrupt Code
4.6.4 Configuration Bits
4.6.5 Linking and Assembling
4.6.6 Command-Line Options
4.6.7 Environment Variables
4.6.8 The Library
4.6.8.1 Enhanced cores
4.6.8.2 Accessing bits of special function registers
4.6.8.3 Naming of special function registers
4.6.8.4 error: missing definition for symbol ``__gptrget1''
4.6.8.5 Processor mismatch in file ``XXX''.
4.6.9 Known Bugs
4.6.9.1 Function arguments
4.6.9.2 Regression tests fail
4.7 The PIC16 port
4.7.1 Global Options
4.7.2 Port Specific Options
4.7.2.1 Code Generation Options
4.7.2.2 Optimization Options
4.7.2.3 Assembling Options
4.7.2.4 Linking Options
4.7.2.5 Debugging Options
4.7.3 Environment Variables
4.7.4 Preprocessor Macros
4.7.5 Directories
4.7.6 Pragmas
4.7.7 Header Files and Libraries
4.7.8 Header Files
4.7.9 Libraries
Building the libraries
Output of float values via printf()
4.7.10 Adding New Devices to the Port
4.7.11 Memory Models
4.7.12 Stack
4.7.13 Functions
4.7.14 Function return values
4.7.15 Interrupts
4.7.16 Generic Pointers
4.7.17 Configuration Bits
4.7.18 PIC16 C Libraries
4.7.18.1 Standard I/O Streams
4.7.18.2 Printing functions
4.7.18.3 Signals
4.7.19 PIC16 Port – Tips
4.7.19.1 Stack size
4.7.20 Known Bugs
4.7.20.1 Extended Instruction Set
4.7.20.2 Regression Tests
Chapter 5 Debugging
5.1 Debugging with SDCDB 
5.1.1 Compiling for Debugging
5.1.2 How the Debugger Works
5.1.3 Starting the Debugger SDCDB
5.1.4 SDCDB Command Line Options
5.1.5 SDCDB Debugger Commands
break [line | file:line | function | file:function]
clear [line | file:line | function | file:function ]
continue
finish
delete [n]
info [break | stack | frame | registers ]
step
next
run
ptype variable 
print variable
file filename
frame
set srcmode
! simulator command
quit
5.1.6 Interfacing SDCDB with DDD
5.1.7 Interfacing SDCDB with XEmacs
5.2 Debugging with other debuggers (e.g. GDB): ELF / DWARF
Chapter 6 TIPS
6.1 Porting code from or to other compilers
6.2 Tools included in the distribution
6.3 Documentation included in the distribution
6.4 Communication online at SourceForge
6.5 Related open source tools
6.6 Related documentation / recommended reading
6.7 Application notes specifically for SDCC
6.8 Some Questions
Chapter 7 Support
7.1 Reporting Bugs
7.2 Requesting Features
7.3 Submitting patches
7.4 Getting Help
7.5 ChangeLog
7.6 Subversion Source Code Repository
7.7 Release policy
7.8 Quality control
7.9 Examples
7.10 Use of SDCC in Education
Chapter 8 SDCC Technical Data
8.1 Optimizations
8.1.1 Sub-expression Elimination
8.1.2 Dead-Code Elimination
8.1.3 Copy-Propagation
8.1.4 Loop Optimizations
8.1.5 Loop Reversing
8.1.6 Algebraic Simplifications
8.1.7 'switch' Statements
8.1.8 Bit-shifting Operations.
8.1.9 Bit-rotation
8.1.10 Nibble and Byte Swapping
8.1.11 Getting a Bit
8.1.12 Higher Order Byte / Higher Order Word
8.1.13 Placement of Bank-Selection Instructions
8.1.14 Lifetime-Optimal Speculative Partial Redundancy Elimination
8.1.15 Register Allocation
8.1.16 Peephole Optimizer
8.2 Cyclomatic Complexity
8.3 Retargetting for other Processors
Chapter 9 Compiler internals
9.1 The anatomy of the compiler
Parsing 
Generating iCode
Optimizations.
Live range analysis
Register Allocation
Code generation
ICode Example
9.2 A few words about basic block successors, predecessors and dominators
Chapter 10 Acknowledgments
Alphabetical index


Introduction

1.1 About SDCC

SDCC (Small Device C Compiler) is free open source, 
retargettable, optimizing standard (ANSI C89 / ISO C90, ISO C99, 
ISO C11 / ISO C17) C compiler suite originally written by Sandeep 
Dutta designed for 8 bit Microprocessors. The current version 
targets Intel MCS51 based Microprocessors (8031, 8032, 8051, 80528031, 8032, 8051, 8052, mcs51 CPU
, etc.), Dallas DS80C390 variants, NXP (formerly 
Freescale/Motorola) HC08 based (hc08, s08), Zilog Z80 based MCUs 
(Z80, Z180, eZ80 in Z80 mode, SM83, Rabbit 2000/3000, Rabbit 
3000A Z80, Z180, SM83, Rabbit 2000/3000, Rabbit 3000A CPU), 
Toshiba TLCS-90, Zilog eZ80 in Z80 mode, STMicroelectronics STM8 STM8
, Padauk PDK14 and PDK15. It can be retargeted for other 
microprocessors, support for Padauk PDK13 and MOS6502 is under 
development, whereas Microchip PIC is currently unmaintained. The 
entire source code for the compiler is distributed under GPL. 
SDCC uses a modified version of ASXXXXsdas (sdasgb, sdas6808, sdas8051, sdasz80)
 & ASLINKsdld, free open source retargetable assembler & linker. 
SDCC has extensive language extensions suitable for utilizing 
various microcontrollers and underlying hardware effectively. 
You might also want to have a look at the wiki https://sourceforge.net/p/sdcc/wiki/
.

In addition to the MCU specific optimizations SDCC also does a 
host of standard optimizations like:

• global sub expression elimination, 

• loop optimizations (loop invariant, strength reduction of 
  induction variables and loop reversing), 

• constant folding & propagation, 

• copy propagation, 

• dead code elimination 

• jump tables for switch statements.

For the back-end SDCC uses a global register allocation scheme 
which should be well suited for other 8 bit MCUs.

The peep hole optimizer uses a rule based substitution mechanism 
which is MCU independent.

Supported data-types are:



+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                             type                                              |            width             | default   |          signed range           |          unsigned range          |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                         _Bool / bool                                          |       8 bits, 1 byte         | unsigned  |               -                 |               0, 1               |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                             char                                              |       8 bits, 1 byte         | unsigned  |           -128, +127            |             0, +255              |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                            short                                              |      16 bits, 2 bytes        |  signed   |        -32.768, +32.767         |            0, +65.535            |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                             int                                               |      16 bits, 2 bytes        |  signed   |        -32.768, +32.767         |            0, +65.535            |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                             long                                              |      32 bits, 4 bytes        |  signed   | -2.147.483.648, +2.147.483.647  |        0, +4.294.967.295         |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|          long long[footnote:
Incomplete support in the pic14 and pic16 backends.
]            |      64 bits, 8 bytes        |  signed   |                                 |                                  |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
| _BitInt[footnote:
Incomplete support in the hc08, s08, mod6502, pic14 and pic16 
backends.
]  | 8 to 64 bits, 1 to 8 bytes   |           |                                 |                                  |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                            float                                              | 4 bytes similar to IEEE 754  |  signed   |                                 | 1.175494351E-38, 3.402823466E+38 |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|                                           pointer                                             |     1, 2, 3 or 4 bytes       | generic   |                                 |                                  |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+
|            __bit[footnote:
Only supported in the mcs51, ds390, ds400 backends.
]              |            1 bit             | unsigned  |               -                 |               0, 1               |
+-----------------------------------------------------------------------------------------------+------------------------------+-----------+---------------------------------+----------------------------------+

The compiler also allows inline assembler code to be embedded 
anywhere in a function. In addition, routines developed in 
assembly can also be called.

SDCC also provides an option (--cyclomatic) to report the 
relative complexity of a function. These functions can then be 
further optimized, or hand coded in assembly if needed.

SDCC also comes with a companion source level debugger SDCDB. The 
debugger currently uses ucSim, a free open source simulator for 
8051 and other micro-controllers.

The latest SDCC version can be downloaded from http://sdcc.sourceforge.net/snap.php
. Please note: the compiler will probably always be some steps 
ahead of this documentationStatus of documentation[footnote:
Obviously this has pros and cons
].

1.2 SDCC Suite Licenses

SDCC suite is a collection of several components derived from 
different sources with different licenses:

• executables:


  – sdcc compiler:
sdcc compiler is licensed under the GPLv2 (GPLv3 might apply 
    depending on the libraries used when building).
The code or object files generated by SDCC suite are not 
    licensed, so they can be used in FLOSS or proprietary (closed 
    source) applications.

  – sdcpp preprocessor:
derived from GCC cpp preprocessor http://gcc.gnu.org/; GPLv3 
    license

  – sdas assemblers and sdld linker:
derived from ASXXXX https://shop-pdp.net/ashtml/; GPLv3 license

  – SDCC run-time libraries:
The great majority of SDCC run-time libraries are licensed under 
    the GPLv2+LEGPLv2+LE which allows linking of SDCC run-time 
    libraries with proprietary (closed source) applications.
A possible exception are pic device libraries and header files 
    which are generated from Microchip header (.inc) and linker 
    script (.lkr) files. Microchip requires that "The header 
    files should state that they are only to be used with 
    authentic Microchip devices" which makes them incompatible 
    with the GPL, if Microchip has any copyright in them (which 
    might depend on local copyright laws). Pic device libraries 
    and header files are located at non-free/lib and 
    non-free/include directories respectively. SDCC should be run 
    with the --use-non-free--use-non-free command line option in 
    order to include non-free header files and libraries. 

  – sdbinutils utilities (sdar, sdranlib, sdnm, sdobjcopy):
derived from GNU Binutils http://www.gnu.org/software/binutils/; 
    GPLv3 license

  – ucsim simulators:
GPLv2 license

  – sdcdb debugger:
GPLv2 license

  – gcc-test regression tests:
derived from gcc-testsuite; no license explicitely specified, but 
    since it is a part of GCC is probably GPLv3 licensed

  – packihx:
public domain

  – makebin:
zlib/libpng License

  – pic libraries in device/non-free:
Microchip Technology Inc. claims to have copyrights on this, and 
    their term are non-free. However, a more common opinion is 
    that Microchip Technology Inc. is just claiming a copyright 
    on uncopyrightable facts.

• libraries:


  – dbuf library:
zlib/libpng License

  – Boost C++ libraries:
http://www.boost.org/; Boost Software License 1.0 (BSL-1.0)

Links to licenses:

• GPLv2 licenseGPLv2 license: http://www.gnu.org/licenses/old-licenses/gpl-2.0.html

• LGPLv2.1 licenseLGPLv2.1 license: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html

• GPLv3 licenseGPLv3 license: http://www.gnu.org/licenses/gpl.html

• zlib/libpng Licensezlib/libpng License: http://www.opensource.org/licenses/Zlib

• Boost Software License 1.0 (BSL-1.0)Boost Software License 1.0 (BSL-1.0)
  : http://www.opensource.org/licenses/BSL-1.0

1.3 Documentation

This documentation is maintained using a free open source word 
processor (LyX) http://www.lyx.org/.

1.4 Typographic conventionsTypographic conventions

Throughout this manual, we will use the following convention. 
Commands you have to type in are printed in "sans serif". Code 
samples are printed in typewriter font. Interesting items and new 
terms are printed in italic.

1.5 Compatibility<sec:Compatibility-with-previous> with previous 
  versionsCompatibility with previous versions

Newer versions have usually numerous bug fixes compared with the 
previous version. But we also sometimes introduce some 
incompatibilities with older versions. Not just for the fun of 
it, but to make the compiler more stable, efficient and standard 
compliantStandard-compliance (see section [subsec:Standard-Compliance]
 for Standard-Compliance). This is a list of such changes .

• short is now equivalent to int (16 bits), it used to be 
  equivalent to char (8 bits) which is not ANSI compliant. To 
  maintain compatibility, old programs could be compiled using 
  the --short-is-8bits command line option (option removed after 
  the 3.6.0 release).

• the default directory for gcc-builds where include, library and 
  documentation files are stored is now in /usr/local/share.

• char type parameters to varargvararg, vaarg functions are 
  casted to int unless explicitly casted and neither of the -
  -std-c89--std-c89, --std-c99--std-c99, --std-c11--std-c11 or -
  -std-c2x--std-c2x command line options is used, e.g.: 
  char a=3;
  printf ("%d %c\n", a, (char)a);
 will push a as an int and as a char resp if none of the above 
  command line options are not defined,
 will push a as two ints if none of the above command line option 
  is defined.

• pointer type parameters to varargvararg, vaarg functions are 
  casted to generic pointers on Harvard architectures (e.g. 
  mcs51, ds390) unless explicitly casted and neither of the -
  -std-c89--std-c89, --std-c99--std-c99, --std-c11--std-c11 or -
  -std-c2x--std-c2x command line options is used.

• option --regextend has been removed.

• option --noregparms has been removed.

• option --stack-after-data has been removed.

• __bitbit and __sbitsbit types now consistently behave like the 
  C99 _Bool type with respect to type conversiontype conversiontype promotion
  . The most common incompatibility resulting from this change is 
  related to bit togglingBit toggling idioms, e.g.:
  __bit b;
  b = ~~ Operatorb; /* equivalent to b=1 instead of toggling b */
  b = !b; /* toggles b */
In previous versions, both forms would have toggled the bit.

• in older versions, the preprocessor was always called with -
  -std-c99--std-c99 regardless of the --std-xxx setting. This is 
  no longer true, and can cause compilation failures on code 
  built with --std-c89--std-c89 but using c99 preprocessor 
  features, such as one-line (//) comments

• in versions older than 2.8.4 the pic16 *printf() and 
  printf_tiny() library functions supported undocumented and not 
  standard compliant 'b' binary format specifier ("%b", "%hb" and 
  "%lb"). The 'b' specifier is now disabled by default. It can be 
  enabled by defining BINARY_SPECIFIER macro in files 
  device/lib/pic16/libc/stdio/vfprintf.c and 
  device/lib/pic16/libc/stdio/printf_tiny.c and recompiling the 
  library.

• in versions older then 2.8.5 the unnamed bit-field structure 
  members participated in initialization, which is not conforming 
  with ISO/IEC 9899:1999 standard (see section Section 6.7.8 
  Initialization, clause 9)

Old behaviour, before version 2.8.5:
  struct {
    int a : 2;
    char  : 2;
    int b : 2;
  } s = {1, 2, 3};
/* s.a = 1, s.b = 3 */

New behaviour:
  struct {
    int a : 2;
    char  : 2;
    int b : 2;
  } s = {1, 2};
/* s.a = 1, s.b = 2 */

• In 2.9.0 libraries included in SDCC packages, are in ar format. 
  See section [subsec:Using-sdar-to].

• In 3.0.0 targets for xa51 and avr are disabled by default.

• In 3.0.0 sdldgb and sdldz80 don't support generation of Game 
  Boy binary image format. The makebin utility can be used to 
  convert Intel Hex format to Game Boy binary image format.

• In 3.0.0 sdldgb and sdldz80 don't support generation of rrgb 
  (Game Boy simulator) map file and no$gmb symbol file formats. 
  The as2gbmap utility can be used to convert sdld map format to 
  rrgb and no$gmb file formats.

• In 3.1.0 asranlib utility was renamed to sdranlib.

• In 3.1.0 pic14 target, structured access to SFR via 
  <sfrname>_bits.<bitname> is deprecated and replaced by 
  <sfrname>bits.<bitname>. It will be obsoleted (removed) in one 
  of next SDCC releases. See section [subsec:Naming-of-special].

• sdar archive managing utility and sdnm utilities were 
  introduced in version 3.2.0. sdar, sdranlib and sdnm are 
  derived from GNU Binutils package.

• In 3.2.0 the sdcclib utility is deprecated. Sdar utility should 
  be used to create SDCC object file archives. Sdcclib utility 
  will become obsolete in one of next SDCC releases and will be 
  removed from SDCC packages.

• In 3.2.0 special SDCC keywords which are not preceded by a 
  double underscore are obsoleted (removed). See section [subsec:Standard-Compliance]
   Standard-Compliance.

• In 3.2.0 compiler macro definitions not starting with double 
  underscore characters are deprecated if --std-cXX command line 
  option is defined. They have been obsoleted (removed) after the 
  3.4.0 release (except for the macro SDCC, which has been 
  removed after the 3.6.0 release (and brought back for mcs51 for 
  the 3.7.0 release)).

• In 3.2.0 new compiler macros for processor definition were 
  introduced for pic14 and pic16 targets: -D__SDCC_PIC16XXXX and 
  -D__SDCC_PIC18FXXX respectively. The pic16 macro definition 
  -D__18fXXX is deprecated. It was obsoleted (removed) after the 
  3.4.0 release.

• In 3.2.0 pragma config for pic16 target was introduced. See 
  section [subsec:PIC16_Pragmas]

• In 3.2.0 new inline assembler format __asm__ 
  (inline_assembler_code”); as an addition to __asm ... 
  __endasem; format introduced. See section [sec:Inline-Assembler-Code]

• sdobjcopy utility was introduced in version 3.3.0. It is 
  derived from GNU Binutils package.

• Before 3.4.0 release, intrinsic named address spaces were 
  called ”storage classes” in this manual.

• In 3.6.0, the default for char changed from signed to unsigned.

• In 3.7.0, the prototype for putchar() changed from void 
  putchar(char) to int putchar(int).

• In 3.7.0 mcs51 and ds390 got a full _Bool/bool type, separate 
  from __bit.

• In 3.7.0, the option –nojtbound and the corresponding pragma 
  have been deprecated.

• In 3.7.0, the prototype for getchar() changed from char 
  getchar(void) to int getchar(void).

• In 3.8.6, the deprecated sdcclib was removed.

• In 4.0.3, _itoa, _uitoa, _ltoa, _ultoa were renamed to __itoa, 
  __uitoa, __ltoa, __ultoa.

• In 4.1.1, typeof.h has been removed.

• In 4.1.3, support for --oldralloc has been removed for the 
  z80-related backends.

• In 4.1.10, the default calling convention switched from 
  __sdccall(0) to __sdccall(1) for stm8 and gbz80.

• In 4.1.10, support for –profile has been removed for gbz80.

• In 4.1.11, the minimum Z80N Core version for the z80n port has 
  been raised from 1.0 to 2.0.

• In 4.1.12, the default calling convention switched from 
  __sdccall(0) to __sdccall(1) for z80, z180 and z80n.

• In 4.1.12, support for –profile has been removed for z80, z180, 
  z80n.

• In 4.1.13, support for –profile has been removed.

• In 4.1.14, the gbz80 port was renamed to sm83.

• In 4.2.3, support for non-parenthesized arguments to __using 
  and __interrupt was dropped.

• In 4.2.3, support for non-parenthesized arguments to __at that 
  are not constants was dropped.

• In 4.2.4, the placement of __at in declarations was restricted.

• In 4.2.6, bool is chosen as the underlying integer type for 
  enumerations with just two values.

• In 4.2.9, support for –pedantic-parse-number and #pragma 
  pedantic_parse_numer was dropped.

• In 4.2.9 support for arguments to -MMD was dropped. The output 
  fiel can be specified via -MF instead.

• In 4.2.10, _sdcc_external_startup was renamed to 
  __sdcc_external_startup and support for it was added to further 
  ports.

• In 4.2.13, for the sm83 port, __sfr addresses need to be 
  specified using the full 16-bit address.

• In 4.2.14, byte order in output from the %p specifier of 
  printf()-family functions was corrected for big-endian 
  platforms (stm8, hc08, s08, mos6502) to match uintptr_t.

1.6 System Requirements

What do you need before you start installation of SDCC? A 
computer, and a desire to compute. The preferred method of 
installation is to compile SDCC from source using GNU GCC and 
make. For Windows some pre-compiled binary distributions are 
available for your convenience. You should have some experience 
with command line tools and compiler use.

1.7 Other Resources

The SDCC home page at http://sdcc.sourceforge.net/ is a great 
place to find distribution sets. You can also find links to the 
user mailing lists that offer help or discuss SDCC with other 
SDCC users. Web links to other SDCC related sites can also be 
found here. This document can be found in the doc directory of 
the source package. The latest snapshot build version of this 
document in pdf format is available at http://sdcc.sourceforge.net/doc/sdccman.pdf
. Some of the other tools (simulator and assembler) included with 
SDCC contain their own documentation and can be found in the 
source distribution. If you want the latest unreleased software, 
the complete source package is available directly from Subversion 
on http://sourceforge.net/p/sdcc/code/8805/tree/trunk/sdcc/.

Installing SDCCInstallation

For most users it is sufficient to skip to either section [subsec:Building-SDCC-on-Linux]
 (Unix) or section [subsec:Windows-Install] (Windows). More 
detailed instructions follow below.

2.1 Configure OptionsOptions SDCC configuration

The install paths, search paths and other options are defined 
when running 'configure'. The defaults can be overridden by:

--prefix see table below

--exec_prefix see table below

--bindir see table below

--datadir see table below

--datarootdir see table below


  docdir environment variable, see table below

  include_dir_suffix environment variable, see table below

  non_free_include_dir_suffix environment variable, see table 
below

  lib_dir_suffix environment variable, see table below

   non_free_lib_dir_suffix environment variable, see table below

  sdccconf_h_dir_separator environment variable, either / or \\ 
makes sense here. This character will only be used in sdccconf.h; 
don't forget it's a C-header, therefore a double-backslash is 
needed there.


--disable-mcs51-port Excludes the Intel mcs51 port

--disable-z80-port Excludes the z80 port

--disable-z180-port Excludes the z180 port

--disable-ez80_z80-port Excludes the e80_z80 port

--disable-r2k-port Excludes the r2k port

--disable-r3ka-port Excludes the r3ka port

--disable-sm83-port Excludes the SM83 port

--disable-avr-port Excludes the AVR port (disabled by default)

--disable-ds390-port Excludes the DS390 port

--disable-hc08-port Excludes the HC08 port

--disable-s08-port Excludes the S08 port

--disable-stm8-port Excludes the STM8 port

--disable-pic-port Excludes the PIC14 port

--disable-pic16-port Excludes the PIC16 port

--disable-xa51-port Excludes the XA51 port (disabled by default)

--disable-ucsim Disables configuring and building of ucsim

--disable-device-lib Disables automatically building device 
libraries

--disable-packihx Disables building packihx

--enable-doc Build pdf, html and txt files from the lyx sources

--enable-libgc Use the Bohem memory allocator. Lower runtime 
footprint.

--without-ccache Do not use ccache even if available

Furthermore the environment variables CC, CFLAGS, ... the tools 
and their arguments can be influenced. Please see `configure -
-help' and the man/info pages of `configure' for details.

The names of the standard libraries STD_LIB, STD_INT_LIB, 
STD_LONG_LIB, STD_FP_LIB, STD_DS390_LIB, STD_XA51_LIB and the 
environment variables SDCC_DIR_NAME, SDCC_INCLUDE_NAME, 
SDCC_LIB_NAME are defined by `configure' too. At the moment it's 
not possible to change the default settings (it was simply never 
required).

These configure options are compiled into the binaries, and can 
only be changed by rerunning 'configure' and recompiling SDCC. 
The configure options are written in italics to distinguish them 
from run time environment variables (see section search paths).

The settings for ”Win32 builds” are used by the SDCC team to 
build the official Win32 binaries. The SDCC team uses Mingw32 to 
build the official Windows binaries, because it's

1. open source, 

2. a gcc compiler and last but not least

3. the binaries can be built by cross compiling on SDCC 
  Distributed Compile Farm.

See the examples, how to pass the Win32 settings to 'configure'. 
The other Win32 builds using VC or whatever don't use 
'configure', but a header file sdcc_vc.h.in is the same as 
sdccconf.h built by 'configure' for Win32.

These defaults are:




+------------------------------+------------------------+------------------+
| Variable                     | default                | Win32 builds     |
+------------------------------+------------------------+------------------+
+------------------------------+------------------------+------------------+
| PREFIX                       | /usr/local             | \sdcc            |
+------------------------------+------------------------+------------------+
| EXEC_PREFIX                  | $PREFIX                | $PREFIX          |
+------------------------------+------------------------+------------------+
| BINDIR                       | $EXEC_PREFIX/bin       | $EXEC_PREFIX\bin |
+------------------------------+------------------------+------------------+
| DATADIR                      | $DATAROOTDIR           | $DATAROOTDIR     |
+------------------------------+------------------------+------------------+
| DATAROOTDIR                  | $PREFIX/share          | $PREFIX          |
+------------------------------+------------------------+------------------+
| DOCDIR                       | $DATAROOTDIR/sdcc/doc  | $DATAROOTDIR\doc |
+------------------------------+------------------------+------------------+
| INCLUDE_DIR_SUFFIX           | sdcc/include           | include          |
+------------------------------+------------------------+------------------+
| NON_FREE_INCLUDE_DIR_SUFFIX  | sdcc/non-free/include  | non-free/include |
+------------------------------+------------------------+------------------+
| LIB_DIR_SUFFIX               | sdcc/lib               | lib              |
+------------------------------+------------------------+------------------+
| NON_FREE_LIB_DIR_SUFFIX      | sdcc/non-free/lib      | non-free/lib     |
+------------------------------+------------------------+------------------+



'configure' also computes relative paths. This is needed for full 
relocatability of a binary package and to complete search paths 
(see section search paths below):
 



+----------------------+-------------+--------------+
| Variable (computed)  | default     | Win32 builds |
+----------------------+-------------+--------------+
+----------------------+-------------+--------------+
| BIN2DATA_DIR         | ../share    | ..           |
+----------------------+-------------+--------------+
| PREFIX2BIN_DIR       | bin         | bin          |
+----------------------+-------------+--------------+
| PREFIX2DATA_DIR      | share/sdcc  |              |
+----------------------+-------------+--------------+



Examples:

./configure
./configure --prefix=”/usr/bin” --datarootdir=”/usr/share”
./configure --disable-avr-port --disable-xa51-port

To cross compile on linux for Mingw32 (see also 
'sdcc/support/scripts/sdcc_mingw32'):

./configure \
CC=”i586-mingw32msvc-gcc” CXX=”i586-mingw32msvc-g++” \
RANLIB=”i586-mingw32msvc-ranlib” \
STRIP=”i586-mingw32msvc-strip” \
--prefix=”/sdcc” \
--datarootdir=”/sdcc” \
docdir=”\${datarootdir}/doc” \
include_dir_suffix=”include” \
non_free_include_dir_suffix=”non-free/include” \
lib_dir_suffix=”lib” \
non_free_lib_dir_suffix=”non-free/lib” \
sdccconf_h_dir_separator=”\\\\” \
--disable-device-lib \
--host=i586-mingw32msvc \
--build=unknown-unknown-linux-gnu

To ”cross”compile on Cygwin for Mingw32 (see also 
sdcc/support/scripts/sdcc_cygwin_mingw32):

./configure -C \
--prefix=”/sdcc” \
--datarootdir=”/sdcc” \
docdir=”\${datarootdir}/doc” \ 
include_dir_suffix=”include” \
non_free_include_dir_suffix=”non-free/include” \
lib_dir_suffix=”lib” \
non_free_lib_dir_suffix=”non-free/lib” \
sdccconf_h_dir_separator=”\\\\” \
CC=”gcc -mno-cygwin” \
CXX=”g++ -mno-cygwin” 

'configure' is quite slow on Cygwin (at least on windows before 
Win2000/XP). The option '--C' turns on caching, which gives a 
little bit extra speed. However if options are changed, it can be 
necessary to delete the config.cache file.

2.2 Install paths<subsec:Install-paths>Install paths


+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Description             | Path                                    | Default                                  | Win32 builds           |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Binary files*           | $EXEC_PREFIX                            | /usr/local/bin                           | \sdcc\bin              |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Include files           | $DATADIR/
$INCLUDE_DIR_SUFFIX           | /usr/local/share/
sdcc/include           | \sdcc\include          |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Non-free include files  | $DATADIR/non-free/
$INCLUDE_DIR_SUFFIX  | /usr/local/share/
sdcc/non-free/include  | \sdcc\non-free\include |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Library file**          | $DATADIR/
$LIB_DIR_SUFFIX               | /usr/local/share/
sdcc/lib               | \sdcc\lib              |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Library file**          | $DATADIR/non-free/
$LIB_DIR_SUFFIX      | /usr/local/share/
sdcc/non-free/lib      | \sdcc\non-free\lib     |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+
| Documentation           | $DOCDIR                                 | /usr/local/share/
sdcc/doc               | \sdcc\doc              |
+-------------------------+-----------------------------------------+------------------------------------------+------------------------+


*compiler, preprocessor, assembler, and linker
**the model is auto-appended by the compiler, e.g. small, large, 
z80, ds390 etc

The install paths can still be changed during `make install' with 
e.g.:

make install prefix=$(HOME)/local/sdcc

Of course this doesn't change the search paths compiled into the 
binaries.

Moreover the install path can be changed by defining DESTDIRDESTDIR
:

make install DESTDIR=$(HOME)/sdcc.rpm/

Please note that DESTDIR must have a trailing slash!

2.3 Search Paths<subsec:Search-Paths>Search path

Some search paths or parts of them are determined by configure 
variables (in italics, see section above). Further search paths 
are determined by environment variables during runtime. 
The paths searched when running the compiler are as follows (the 
first catch wins):

1. Binary files (preprocessor, assembler and linker)




+---------------------------------+------------------+-----------------+
| Search path                     | default          | Win32 builds    |
+---------------------------------+------------------+-----------------+
+---------------------------------+------------------+-----------------+
| $SDCC_HOME/$PPREFIX2BIN_DIR     | $SDCC_HOME/bin   | $SDCC_HOME\bin  |
+---------------------------------+------------------+-----------------+
| Path of argv[0] (if available)  | Path of argv[0]  | Path of argv[0] |
+---------------------------------+------------------+-----------------+
| $PATH                           | $PATH            | $PATH           |
+---------------------------------+------------------+-----------------+
 


2. Include files




+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| #  | Search path                                                  | default                                  | Win32 builds                      |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 1  | --I dir                                                      | --I dir                                  | --I dir                           |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 2  | $SDCC_INCLUDE                                                | $SDCC_INCLUDE                            | $SDCC_INCLUDE                     |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 3  | $SDCC_HOME/
$PREFIX2DATA_DIR/
$INCLUDE_DIR_SUFFIX            | $SDCC_HOME/
share/sdcc/include           | $SDCC_HOME\include                |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 4  | path(argv[0])/
$BIN2DATADIR/
$INCLUDE_DIR_SUFFIX             | path(argv[0])/../
sdcc/include           | path(argv[0])\..\include          |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 5  | $DATADIR/
$INCLUDE_DIR_SUFFIX                                | /usr/local/share/
sdcc/include           | (not on Win32)                    |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 6  | $SDCC_HOME/
$PREFIX2DATA_DIR/
non-free/
$INCLUDE_DIR_SUFFIX  | $SDCC_HOME/share/
sdcc/non-free/include  | $SDCC_HOME\non-free\include       |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 7  | path(argv[0])/
$BIN2DATADIR/
non-free/
$INCLUDE_DIR_SUFFIX   | path(argv[0])/../
sdcc/non-free/include  | path(argv[0])\..\non-free\include |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
| 8  | $DATADIR/
non-free/
$INCLUDE_DIR_SUFFIX                      | /usr/local/share/
sdcc/non-free/include  | (not on Win32)                    |
+----+--------------------------------------------------------------+------------------------------------------+-----------------------------------+
 


The option --nostdinc disables all search paths except #1 and #2.

3. Library files


With the exception of ”--L dir” the model is auto-appended by the 
compiler (e.g. small, large, z80, ds390 etc.).




+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| #  | Search path                                                       | default                                       | Win32 builds                           |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 1  | --L dir                                                           | --L dir                                       | --L dir                                |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 2  | $SDCC_LIB/<model>                                                 | $SDCC_LIB/<model>                             | $SDCC_LIB/<model>                      |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 3  | $SDCC_LIB                                                         | $SDCC_LIB                                     | $SDCC_LIB                              |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 4  | $SDCC_HOME/
$PREFIX2DATA_DIR/
$LIB_DIR_SUFFIX/
<model>            | $SDCC_HOME/
share/sdcc/lib/<model>            | $SDCC_HOME\
lib\<model>                |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 5  | path(argv[0])/
$BIN2DATADIR/
$LIB_DIR_SUFFIX/
<model>             | path(argv[0])/../sdcc/
lib/<model>            | path(argv[0])\
..\lib\
<model>         |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 6  | $DATADIR/non-free/
$LIB_DIR_SUFFIX/
<model>                       | /usr/local/share/sdcc/
lib/<model>            | (not on Win32)                         |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 7  | $SDCC_HOME/
$PREFIX2DATA_DIR/
non-free/
$LIB_DIR_SUFFIX/
<model>  | $SDCC_HOME/share/sdcc/
non-free/lib/<model>   | $SDCC_HOME\
lib\non-free\<model>       |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 8  | path(argv[0])/
$BIN2DATADIR/
non-free/
$LIB_DIR_SUFFIX/
<model>   | path(argv[0])/../sdcc/
non-free/lib/<model>   | path(argv[0])\..\
lib\non-free\<model> |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+
| 9  | $DATADIR/non-free/
$LIB_DIR_SUFFIX/
<model>                       | /usr/local/share/sdcc/
non-free/lib/
<model>  | (not on Win32)                         |
+----+-------------------------------------------------------------------+-----------------------------------------------+----------------------------------------+





 
The option --nostdlib disables all search paths except #1 and #2.

2.4 Building SDCCBuilding SDCC

SDCC can be built for various host platforms using the 
instructions provided below. Note that the PIC14 and PIC16 
library folders in the source distribution contain 
Autotools-generated files. These are included for convenience and 
to avoid introducing Autotools as an additional dependency. They 
have to be regenerated in case of a version mismatch. 
Alternatively, the PIC backends can be disabled.

2.4.1 Building SDCC on Linux<subsec:Building-SDCC-on-Linux>

1. Download the source package either from the SDCC Subversion 
  repository or from snapshot builds, it will be named something 
  like sdcc-src-yyyymmdd-rrrr.tar.bz2 http://sdcc.sourceforge.net/snap.php
  .

2. Bring up a command line terminal, such as xterm.

3. Unpack the file using a command like: "tar -xvjf 
  sdcc-src-yyyymmdd-rrrr.tar.bz2”, this will create a 
  sub-directory called sdcc with all of the sources.

4. Change directory into the main SDCC directory, for example 
  type: "cd sdcc".

5. Type "./configure". This configures the package for 
  compilation on your system. When the treedec library is 
  available, it should be found and used automatically (improving 
  the compilation time / code quality trade-off). As of SDCC 
  3.7.0, the current develop branch from 
  https://github.com/freetdi/tdlib is a suitable version of 
  treedec.

6. Type "make". All of the source packages will compile, this can 
  take a while.

7. Type "make install" as root. This copies the binary 
  executables, the include files, the libraries and the 
  documentation to the install directories. Proceed with section [sec:Testing-the-SDCC]
  .

2.4.2 Building SDCC on Mac OS X

Follow the instruction for Linux.

On Mac OS X 10.2.x it was reported, that the default gcc (version 
3.1 20020420 (prerelease)) fails to compile SDCC. Fortunately 
there's also gcc 2.9.x installed, which works fine. This compiler 
can be selected by running 'configure' with:

./configure CC=gcc2 CXX=g++2

Universal (ppc and i386) binaries can be produced on Mac OS X 
10.4.x with Xcode. Run 'configure' with:

./configure \

LDFLAGS="-Wl,-syslibroot,/Developer/SDKs/MacOSX10.4u.sdk -arch 
i386 -arch ppc" \

CXXFLAGS = "-O2 -isysroot /Developer/SDKs/MacOSX10.4u.sdk -arch 
i386 -arch ppc" \

CFLAGS = "-O2 -isysroot /Developer/SDKs/MacOSX10.4u.sdk -arch 
i386 -arch ppc"

2.4.3 Cross compiling SDCC on Linux for Windows

With the MinGW gcc cross compiler SDCC can be cross-compiled for 
Win32. See section 'Configure Options'. SDCC requires boost, but 
the header-only parts should be sufficient: Get a current boost 
tarball from www.boost.org, unpack it, and choose suitable 
configure options so the headers are found by the C++ compiler.

2.4.4 Building SDCC using Cygwin and Mingw32

For building and installing a Cygwin executable follow the 
instructions for Linux.

On Cygwin a ”native” Win32-binary can be built, which will not 
need the Cygwin-DLL. For the necessary 'configure' options see 
section 'configure options' or the script 
'sdcc/support/scripts/sdcc_cygwin_mingw32'.

In order to install Cygwin on Windows download setup.exe from 
www.cygwin.com http://www.cygwin.com/. Run it, set the ”default 
text file type” to ”unix” and download/install at least the 
following packages. Some packages are selected by default, others 
will be automatically selected because of dependencies with the 
manually selected packages. Never deselect these packages!

• flex

• bison

• gcc ; version 3.x is fine, no need to use the old 2.9x

• binutils ; selected with gcc

• make

• libboost-dev

• rxvt ; a nice console, which makes life much easier under 
  windoze (see below)

• man ; not really needed for building SDCC, but you'll miss it 
  sooner or later

• less ; not really needed for building SDCC, but you'll miss it 
  sooner or later

• svn ; only if you use Subversion access

If you want to develop something you'll need:

• python ; for the regression tests

• gdb ; the gnu debugger, together with the nice GUI ”insight”

• openssh ; to access the CF or commit changes

• autoconf and autoconf-devel ; if you want to fight with 
  'configure', don't use autoconf-stable!

rxvt is a nice console with history. Replace in your cygwin.bat 
the line

bash --login -i 

with (one line):

rxvt -sl 1000 -fn "Lucida Console-12" -sr -cr red

     -bg black -fg white -geometry 100x65 -e bash --login

Text selected with the mouse is automatically copied to the 
clipboard, pasting works with shift-insert.

The other good tip is to make sure you have no //c/-style paths 
anywhere, use /cygdrive/c/ instead. Using // invokes a network 
lookup which is very slow. If you think ”cygdrive” is too long, 
you can change it with e.g.

mount -s -u -c /mnt

SDCC sources use the unix line ending LF. Life is much easier, if 
you store the source tree on a drive which is mounted in binary 
mode. And use an editor which can handle LF-only line endings. 
Make sure not to commit files with windows line endings. The 
tabulator spacingtabulator spacing (8 columns) used in the 
project is 8. Although a tabulator spacing of 8 is a sensible 
choice for programmers (it's a power of 2 and allows to display 
8/16 bit signed variables without loosing columns) the plan is to 
move towards using only spaces in the source.

2.4.5 Building SDCC Using Microsoft Visual C++ 2010 (MSVC)

Download the source package either from the SDCC Subversion 
repository or from the snapshot builds http://sdcc.sourceforge.net/snap.php
, it will be named something like sdcc-src-yyyymmdd-rrrr.tar.bz2. 
SDCC is distributed with all the project, solution and other 
files you need to build it using Visual C++ 2010 (except for 
ucSim). The solution name is 'sdcc.sln'. Please note that as it 
is now, all the executables are created in a folder called 
sdcc\bin_vc. Once built you need to copy the executables from 
sdcc\bin_vc to sdcc\bin before running SDCC. 

Apart from the SDCC sources you also need to have the BOOST 
libraries installed for MSVC. Get it here http://www.boost.org/

In order to build SDCC with MSVC you need win32 executables of 
bison.exe, flex.exe, and gawk.exe. One good place to get them is 
here http://unxutils.sourceforge.net

If UnxUtils didn't work well, msysmsys (http://www.mingw.org/wiki/msys
) or msys2msys2(https://msys2.github.io) can be an alternative.

Download the file UnxUtilsUnxUtils.zip. Now you have to install 
the utilities and setup MSVC so it can locate the required 
programs. Here there are two alternatives (choose one!):

1. The easy way:

a) Extract UnxUtils.zip to your C:\ hard disk PRESERVING the 
  original paths, otherwise bison won't work. (If you are using 
  WinZip make certain that 'Use folder names' is selected)

b) Add 'C:\user\local\wbin' to VC++ Directories / Executable 
  Directories.

(As a side effect, you get a bunch of Unix utilities that could 
  be useful, such as diff and patch.)

2. A more compact way:

This one avoids extracting a bunch of files you may not use, but 
  requires some extra work:

a) Create a directory were to put the tools needed, or use a 
  directory already present. Say for example 'C:\util'.

b) Extract 'bison.exe', 'bison.hairy', 'bison.simple', 
  'flex.exe', and gawk.exe to such directory WITHOUT preserving 
  the original paths. (If you are using WinZip make certain that 
  'Use folder names' is not selected)

c) Rename bison.exe to '_bison.exe'.

d) Create a batch file 'bison.bat' in 'C:\util\' and add these 
  lines:
  set BISON_SIMPLE=C:\util\bison.simple 
  set BISON_HAIRY=C:\util\bison.hairy
  _bison %1 %2 %3 %4 %5 %6 %7 %8 %9

Steps 'c' and 'd' are needed because bison requires by default 
  that the files 'bison.simple' and 'bison.hairy' reside in some 
  weird Unix directory, '/usr/local/share/' I think. So it is 
  necessary to tell bison where those files are located if they 
  are not in such directory. That is the function of the 
  environment variables BISON_SIMPLE and BISON_HAIRY.

e) Add 'C:\util' to VC++ Directories / Executable Directories. 
  Note that you can use any other path instead of 'C:\util', even 
  the path where the Visual C++ tools are, probably: 'C:\Program 
  Files\Microsoft Visual Studio\Common\Tools'. So you don't have 
  to execute step 'e' :)

That is it. Open 'sdcc.sln' in Visual Studio, click 'build all', 
when it finishes copy the executables from sdcc\bin_vc to 
sdcc\bin, and you can compile using SDCC.

2.4.6 Windows Install Using a ZIP Package

1. Download the binary zip package from http://sdcc.sf.net/snap.php
   and unpack it using your favorite unpacking tool (gunzip, 
  WinZip, etc). This should unpack to a group of sub-directories. 
  An example directory structure after unpacking the mingw32 
  package is: C:\sdcc\bin for the executables, C:\sdcc\include 
  and C:\sdcc\lib for the include and libraries.

2. Adjust your environment variable PATH to include the location 
  of the bin directory or start sdcc using the full path.

2.4.7 Windows Install Using the Setup Program<subsec:Windows-Install>

Download the setup program sdcc-x.y.z-setup.exe for an official 
release from
http://sourceforge.net/projects/sdcc/files/ or a setup program 
for one of the snapshots sdcc-yyyymmdd-xxxx-setup.exe from http://sdcc.sourceforge.net/snap.php
 and execute it. A windows typical installer will guide you 
through the installation process.

2.4.8 VPATHVPATH feature

SDCC supports the VPATH feature provided by configure and make. 
It allows to separate the source and build trees. Here's an 
example:

cd ~                                    # cd $HOME

tar -xjf sdcc-src-yyyymmdd-rrrr.tar.bz2 # extract source to 
directory sdcc

mkdir sdcc.build                        # put output in 
sdcc.build

cd sdcc.build

../sdcc/configure                       # configure is doing all 
the magic!

make

That's it! configure will create the directory tree will all the 
necessary Makefiles in ~/sdcc.build. It automagically computes 
the variables srcdir, top_srcdir and top_buildir for each 
directory. After running make the generated files will be in 
~/sdcc.build, while the source files stay in ~/sdcc.
This is not only usefull for building different binaries, e.g. 
when cross compiling. It also gives you a much better overview in 
the source tree when all the generated files are not scattered 
between the source files. And the best thing is: if you want to 
change a file you can leave the original file untouched in the 
source directory. Simply copy it to the build directory, edit it, 
enter `make clean', `rm Makefile.dep' and `make'. make will do 
the rest for you!

2.5 Building the Documentation

Add --enable-doc to the configure arguments to build the 
documentation together with all the other stuff. You will need 
several tools (LyX, LaTeX, LaTeX2HTML, pdflatex, dvipdf, dvips 
and makeindex) to get the job done. Another possibility is to 
change to the doc directory and to type ”make” there. You're 
invited to make changes and additions to this manual 
(sdcc/doc/sdccman.lyx). Using LyX http://www.lyx.org as editor is 
straightforward. Prebuilt documentation is available from http://sdcc.sourceforge.net/snap.php
.

2.6 Reading the DocumentationDocumentation

Currently reading the document in PDF format is recommended, as 
for unknown reason the hyperlinks are working there whereas in 
the HTML version they are not[footnote:
If you should know why please drop us a note
].
You'll find the PDF versionPDF version of this document at http://sdcc.sourceforge.net/doc/sdccman.pdf
.
This documentation is in some aspects different from a commercial 
documentation: 

• It tries to document SDCC for several processor architectures 
  in one document (commercially these probably would be separate 
  documents/products). This documentStatus of documentation 
  currently matches SDCC for mcs51 and DS390 best and does give 
  too few information about f.e. Z80, PIC14, PIC16 and HC08.

• There are many references pointing away from this 
  documentation. Don't let this distract you. If there f.e. was a 
  reference like http://www.opencores.org together with a 
  statement ”some processors which are targeted by SDCC can be 
  implemented in a field programmable gate arrayFPGA (field programmable gate array)
  ” or http://sourceforge.net/projects/fpgac/FpgaC ((subset of) C to FPGA compiler)
   ”have you ever heard of an open source compiler that compiles 
  a subset of C for an FPGA?” we expect you to have a quick look 
  there and come back. If you read this you are on the right 
  track.

• Some sections attribute more space to problems, restrictions 
  and warnings than to the solution.

• The installation section and the section about the debugger is 
  intimidating.

• There are still lots of typos and there are more different 
  writing styles than pictures.

2.7 Testing the SDCC Compiler<sec:Testing-the-SDCC>

The first thing you should do after installing your SDCC compiler 
is to see if it runs. Type "sdcc --version"version at the prompt, 
and the program should run and output its version like: 
SDCC : mcs51/z80/avr/ds390/pic16/pic14/ds400/hc08 2.5.6 #4169 
(May 8 2006) (UNIX)

If it doesn't run, or gives a message about not finding sdcc 
program, then you need to check over your installation. Make sure 
that the sdcc bin directory is in your executable search path 
defined by the PATH environment setting (see section [subsec:Install-Trouble-shooting]
 Install trouble-shooting for suggestions). Make sure that the 
sdcc program is in the bin folder, if not perhaps something did 
not install correctly.

SDCC is commonly installed as described in section ”Install and 
search paths”.

Make sure the compiler works on a very simple example. Type in 
the following test.c program using your favorite ASCII editor:

char test;

void main(void) {
    test=0;
}

Compile this using the following command: "sdcc -c test.c". If 
all goes well, the compiler will generate a test.asm and test.rel 
file. Congratulations, you've just compiled your first program 
with SDCC. We used the -c option to tell SDCC not to link the 
generated code, just to keep things simple for this step.

The next step is to try it with the linker. Type in "sdcc 
test.c". If all goes well the compiler will link with the 
libraries and produce a test.ihx output file. If this step fails 
(no test.ihx, and the linker generates warnings), then the 
problem is most likely that SDCC cannot find the 
/usr/local/share/sdcc/lib directory (see section [subsec:Install-Trouble-shooting]
 Install trouble-shooting for suggestions).

The final test is to ensure SDCC can use the standard header 
files and libraries. Edit test.c and change it to the following:

#include <string.h>

char str1[10];

void main(void) {
  strcpy(str1, "testing");
}

Compile this by typing "sdcc test.c". This should generate a 
test.ihx output file, and it should give no warnings such as not 
finding the string.h file. If it cannot find the string.h file, 
then the problem is that SDCC cannot find the 
/usr/local/share/sdcc/include directory (see the section [subsec:Install-Trouble-shooting]
 Install trouble-shooting section for suggestions). Use option -
-print-search-dirs--print-search-dirs to find exactly where SDCC 
is looking for the include and lib files.

2.8 Install Trouble-shooting<subsec:Install-Trouble-shooting>Install trouble-shooting

2.8.1 If SDCC does not build correctly

A thing to try is starting from scratch by unpacking the .tgz 
source package again in an empty directory. Configure it like:

./configure 2>&1 | tee configure.log

and build it like:

make 2>&1 | tee make.log

If anything goes wrong, you can review the log files to locate 
the problem. Or a relevant part of this can be attached to an 
email that could be helpful when requesting help from the mailing 
list.

2.8.2 What the ”./configure” does

The ”./configure” command is a script that analyzes your system 
and performs some configuration to ensure the source package 
compiles on your system. It will take a few minutes to run, and 
will compile a few tests to determine what compiler features are 
installed.

2.8.3 What the ”make” does

This runs the GNU make tool, which automatically compiles all the 
source packages into the final installed binary executables.

2.8.4 What the ”make install” command does.

This will install the compiler, other executables libraries and 
include files into the appropriate directories. See sections [subsec:Install-paths]
, [subsec:Search-Paths] about install and search paths.
On most systems you will need super-user privileges to do this.

2.9 Components of SDCC

SDCC is not just a compiler, but a collection of tools by various 
developers. These include linkers, assemblers, simulators and 
other components. Here is a summary of some of the components. 
Note that the included simulator and assembler have separate 
documentation which you can find in the source package in their 
respective directories. As SDCC grows to include support for 
other processors, other packages from various developers are 
included and may have their own sets of documentation.

You might want to look at the files which are installed in 
<installdir>. At the time of this writing, we find the following 
programs for gcc-builds:
 
In <installdir>/bin:

• sdcc - The compiler.

• sdcpp - The C preprocessor.

• sdas8051 - The assembler for 8051 type processors.

• sdas390 - The assembler for DS80C390 processor.

• sdasz80, sdasgb - The Z80 and GameBoy Z80 assemblers.

• sdas6808 - The 6808 assembler.

• sdasstm8 - The STM8 assembler.

• sdld -The linker for 8051 and STM8 type processors.

• sdldz80, sdldgb - The Z80 and GameBoy Z80 linkers.

• sdld6808 - The 6808 linker.

• s51 - The ucSim 8051 simulator.

• sz80 - The ucSim Z80 simulator.

• shc08 - The ucSim 6808 simulator.

• sstm8 - The ucSim STM8 simulator.

• sdcdb - The source debugger.

• sdar, sdranlib, sdnm, sdobjcopy - The sdcc archive managing and 
  indexing utilites.

• packihx - A tool to pack (compress) Intel hex files.

• makebin - A tool to convert Intel Hex file to a binary and 
  GameBoy binary image file format.

In <installdir>/share/sdcc/include

• the include files

In <installdir>/share/sdcc/non-free/include

• the non-free include files

In <installdir>/share/sdcc/lib

• the src and target subdirectories with the precompiled 
  relocatables.

In <installdir>/share/sdcc/non-free/lib

• the src and target subdirectories with the non-free precompiled 
  relocatables.

In <installdir>/share/sdcc/doc

• the documentation

2.9.1 sdcc - The Compiler

This is the actual compiler, it in turn uses the C-preprocessor 
and invokes the assembler and linkage editor.

2.9.2 sdcpp - The C-PreprocessorPreprocessor

The preprocessorsdcpp (preprocessor) is a modified version of the 
GNU cppcpp|seesdcpp preprocessor http://gcc.gnu.org/. The C 
preprocessor is used to pull in #include sources, process #ifdef 
statements, #defines and so on.

2.9.3 sdas, sdld - The Assemblers and Linkage Editors

This is a set of retargettable assemblers and linkage editors, 
which was developed by Alan Baldwin. John Hartman created the 
version for 8051, and I (Sandeep) have made some enhancements and 
bug fixes for it to work properly with SDCC. 

SDCC used an about 1998 branch of asxxxx version 2.0 which 
unfortunately is not compatible with the more advanced (f.e. 
macros, more targets) ASxxxx Cross Assemblers nowadays available 
from Alan Baldwin https://shop-pdp.net/. In 2009 Alan made his 
ASxxxx Cross Assemblers version 5.0 available under the GPL 
license (GPLv3 or later), so a reunion is now a work in progress. 
Thanks Alan!

2.9.4 s51, sz80, shc08, sstm8 - The Simulators

s51s51 (simulator), sz80sz80 (simulator) shc08shc08 (simulator) 
and sstm8 sstm8 (simulator) are free open source simulators 
developed by Daniel Drotos. The simulators are built as part of 
the build process. For more information visit Daniel's web site 
at: http://mazsola.iit.uni-miskolc.hu/~drdani/embedded/s51. It 
currently supports the core mcs51, the Dallas DS80C390, the 
Phillips XA51 family, the Z80, 6808 and the STM8.

2.9.5 sdcdb - Source Level Debugger

SDCDBSDCDB (debugger) is the companion source level debugger. 
More about SDCDB in section [cha:Debugging-with-SDCDB]. The 
current version of the debugger uses Daniel's Simulator S51s51 (simulator)
, but can be easily changed to use other simulators.

Using SDCC

3.1 Standard-ComplianceStandard-compliance<subsec:Standard-Compliance>

SDCC aims to be a conforming freestanding implementation of the C 
programming language. The latest publicly available version of 
the standard ISO/IEC 9899 - Programming languages - C should be 
available at: http://www.open-std.org/jtc1/sc22/wg14/www/standards.html#9899
.

3.1.1 ISO C90 and ANSI C89

Use --std-c89--std-c89 to compile in this mode.



Deviations from standard compliance:

• initialization of structure arrays must be fully braced.


  struct s { char x } a[] = {1, 2};     /* invalid in SDCC */
struct s { char x } a[] = {{1}, {2}}; /* OK */

• 'doubledouble (not supported)' precision floating point Floating point support
  not supported. Instead a warning is emitted, and float is used 
  instead. long double is treated the same.

• K&R styleKR style function declarations are not supported.


  foo(i,j) /* this old style of function declarations */
int i,j; /* is valid in ANSI but not valid in SDCC */
{ 
    ... 
}

Some features of this standard are not supported in some ports:

• hc08, s08, mos6502, pic14, pic16: structuresstruct and unionsunion
   cannot be passed as function parameters and cannot be a return 
  valuereturn value from a function, e.g.:


  struct s { ... };
struct s foo1 (struct s parms) /* invalid in SDCC although 
  allowed in ANSI */
{
    struct s rets;
    ...
    return rets; /* is invalid in SDCC although allowed in ANSI 
  */
}

• mcs51, ds390, hc08, s08, pdk13, pdk14, pdk15 and mos6502 ports: 
  functions are not reentrant unless explicitly declared as such 
  or --stack-auto is specified.

3.1.2 ISO C95

Use --std-c95--std-c95 to compile in this mode.

Except for the issues mentioned in the section above, this 
standard is supported.

3.1.3 ISO C99

Use --std-c99--std-c99 to compile in this mode.

In addition to what is mentioned in the section above, the 
following features of this standard are not supported by SDCC:

• Compound literals. 

• Objects of variably-modified types.

• ptrdiff_t has 16 bits, while the standard requires at least 17 
  bits.

Some features of this standard are not supported in some ports:

• pic14, pic16: there is no support for data types long long, 
  unsigned long long, int_fast64_t, int_least64_t, int64_t, 
  uint_fast64_t, uint_least64_t, uint64_t. 

3.1.4 ISO C11 and ISO C17

Use --std-c11--std-c11 to compile in this mode.

Except for the issues mentioned in the section above, this 
standard is supported.

3.1.5 ISO C2X

Use --std-c2x--std-c2x to compile in this mode.

Deviations from standard compliance:

• initialization of structure arrays must be fully braced.


  struct s { char x } a[] = {1, 2};     /* invalid in SDCC */
struct s { char x } a[] = {{1}, {2}}; /* OK */

• 'doubledouble (not supported)' precision floating point Floating point support
  not supported. Instead a warning is emitted, and float is used 
  instead. long double is treated the same.

• Compund literals are not supported.

• Support for attributes is slightly incomplete.

• The preprocessor is not C2X-compatible.

• Checked integer arithmetic is not supported for (unsigned) long 
  long.

• Qualifier-preserving standard library functions are not 
  implemented.

• Enhanced enumerations are not implemented.

• constexpr is not implemented.

• SDCC deviates from the current C2X standard draft N3047 in tag 
  compatibility for unions: in SDCC, redeclarations of unions are 
  required to have their members in the same order as previous 
  declarations. The rule in N3047 is now considered a mistake by 
  many, and will hopefully be changed to the SDCC behaviour via a 
  national body comment for the final version of the standard.

Some features of this standard are not supported in some ports:

• hc08, s08, mos6502, pic14, pic16: structuresstruct and unionsunion
   cannot be passed as function parameters and cannot be a return 
  valuereturn value from a function, e.g.:


  struct s { ... };
struct s foo1 (struct s parms) /* invalid in SDCC although 
  allowed in ANSI */
{
    struct s rets;
    ...
    return rets; /* is invalid in SDCC although allowed in ANSI 
  */
}

• mcs51, ds390, hc08, s08, pdk13, pdk14, pdk15 and mos6502 ports: 
  functions are not reentrant unless explicitly declared as such 
  or --stack-auto is specified.

• pic14, pic16: there is no support for data types long long, 
  unsigned long long, int_fast64_t, int_least64_t, int64_t, 
  uint_fast64_t, uint_least64_t, uint64_t. 

• pic14, pic16: _BitInt is not supported.

3.1.6 Embedded C

SDCC supports objects in named address spaces and to some degree 
pointers to such objects. The support for fixed-point math in 
SDCC is inconsistent with the standard. Other parts of the 
standard are not supported.

3.1.7 Implementation-defined behavior

3.1.7.1 Translation

• Diagnostics are output to stderr, in the format 
  <filename>:<line-number>: <warning|error> <diagnostic-number>: 
  <diagnostic-description>

• Nonempty sequences of white-space are retained in translation 
  phase 3.

3.1.7.2 Environment

• See SDCC source (and your own code if you use a custom crt0 for 
  a target that supports it) for any information on the 
  environment.

3.1.7.3 Identifiers

• See the compiler and assembler source for information on 
  characters that may appear in identifiers and on the number of 
  significant initial characters.

3.1.7.4 Characters

• There are 8 bits in a byte.

• Values of members of the execution character set: TODO.

• Values of members of the execution character set for escape 
  sequences: TODO.

• Value of char with something weird stored in it: TODO.

• unsigned char has the same range, representation and behavior 
  as ”plain” char.

• See the SDCC source for further information on character sets.

3.1.7.5 Integers

• There are no extended integer types.

3.1.7.6 Floating point

• See the implementation (soft float library) for any information 
  on floating point.

3.1.7.7 Arrays and Pointers

• For the result of converting between pointers and integers see 
  the SDCC source code.

• For the size of the result of subtracting two pointers to 
  elements of the same array see the SDCC source code.

3.1.7.8 Hints

• The extend to which suggestions made by register are effective 
  depends on the target.

• SDCC will inline functions if and only if they are declared 
  using inline and do not have variable arguments.

3.1.7.9 Structures, unions, enumerations and bit-fields

• A plain int bit-field is treated as an unsigned int bit-field.

• There are no allowed bit-field types other than _Bool, signed 
  int and unsigned int.

• Atomic types are not permitted for bit-fields.

• If a bit-fields does not fit into the same byte as the previous 
  bit-fields, it starts on the next byte.

• bit-fields are allocated in the same order as they appear in 
  the source.

• Non-bit-field members of structures are aligned on byte 
  boundaries (i.e. there are no padding bytes).

• For enumerations, the compatible type is the first from the 
  following list that fits the constants: bool, unsigned char, 
  signed char, unsigned int, signed int, unsigned long int, 
  signed long int, unsigned long long int, signed long long int.

3.1.7.10 Qualifiers

• SDCC shall preserve all volatile reads and writes, but does not 
  guarantee them to be atomic (except for atomic types and 
  volatile sig_atomic_t).

3.1.7.11 Preprocessing directives

• See the preprocessor source for information on preprocessing 
  directives.

3.1.7.12 Library functions

• See the respective library headers for the library functions 
  available.

• See assert.h and library source for the format of the 
  diagnostic printed by the assert macro.

• There is no fegetexceptflag function.

• There is no feraiseexcept function.

• There is no setlocale function.

• There is no FLT_EVAL_METHOD macro.

• There is no DEC_EVAL_METHOD macro.

• There are no non-required domain errors for mathematics 
  functions.

• See library source for the values returned by mathematical 
  functions on domain error and pole error (and anything else on 
  mathematical functions and floating type encodings).

• See library headers for the null-pointer constant to which NULL 
  expands.

• See library headers and source for anything else about the 
  library.

3.1.7.13 Architecture

• See the respective library headers for the values or 
  expressions for macros specified in float.h, limits.h, 
  stdint.h.

• Multithreading is not supported.

• The number of bytes in any object is the minimum allowed 
  (except for some padding bits on bit-fields), byte order 
  depends on the target.

• No extended alignments are supported.

• There are no valid alignments other than those returned by 
  _Alignof.

• sizeof always returns the smallest value allowed assuming an 
  8-bit char. _Alignof always returns 0.

3.2 Compiling

3.2.1 Single Source File Projects

For single source file 8051 projects the process is very simple. 
Compile your programs with the following command "sdcc 
sourcefile.c". This will compile, assemble and link your source 
file. Output files are as follows:

• sourcefile.asm<file>.asm - Assembler sourceAssembler source 
  file created by the compiler

• sourcefile.lst<file>.lst - Assembler listingAssembler listing 
  file created by the Assembler

• sourcefile.rst<file>.rst - Assembler listingAssembler listing 
  file updated with linkedit information, created by linkage 
  editor

• sourcefile.sym<file>.sym - symbol listingSymbol listing for the 
  sourcefile, created by the assembler

• sourcefile.rel<file>.rel - Object fileObject file created by 
  the assembler, input to Linkage editor

• sourcefile.map<file>.map - The memory mapMemory map for the 
  load module, created by the Linker

• sourcefile.mem<file>.mem - A file with a summary of the memory 
  usage

• sourcefile.ihx<file>.ihx - The load module in Intel hex formatIntel hex format
   (you can select the Motorola S19 formatMotorola S19 format 
  with --out-fmt-s19--out-fmt-s19. If you need another format you 
  might want to use objdumpobjdump (tool) or srecordsrecord (bin, hex, ... tool)
   - see also section [subsec:Postprocessing-the-Intel]). Both 
  formats are documented in the documentation of srecordsrecord (bin, hex, ... tool)

• sourcefile.adb<file>.adb - An intermediate file containing 
  debug information needed to create the .cdb file (with --debug--debug
  ) 

• sourcefile.cdb<file>.cdb - An optional file (with --debug) 
  containing debug information. The format is documented in 
  cdbfileformat.pdf

• sourcefile.omf<file>.omf - An optional AOMF or AOMF51AOMF, AOMF51
   <OMF file>file containing debug information (generated with 
  option --debug). The (Intel) absolute object module format is a 
  subformat of the OMF51 format and is commonly used by third 
  party tools (debuggersDebugger, simulators, emulators).

• sourcefile.dump*<file>.dump* - Dump file to debug the compiler 
  it self (generated with option --dumpall) (see section [subsec:Intermediate-Dump-Options]
    and section [subsec:The-anatomy-of] ”Anatomy of the compiler”
  ).

3.2.2 Postprocessing the Intel HexIntel hex format file<subsec:Postprocessing-the-Intel>

In most cases this won't be needed but the Intel Hex file<file>.ihx
 which is generated by SDCC might include lines of varying length 
and the addresses within the file are not guaranteed to be 
strictly ascending. If your toolchain or a bootloader does not 
like this you can use the tool packihxpackihx (tool) which is 
part of the SDCC distribution: 

 packihx sourcefile.ihx >sourcefile.hex

The separately available srecordsrecord (bin, hex, ... tool) 
package additionally allows to set undefined locations to a 
predefined value, to insert checksumschecksum of various flavours 
(crc, add, xor) and to perform other manipulations (convert, 
split, crop, offset, ...). 

srec_cat  sourcefile.ihx -intel  -o sourcefile.hex -intel

An example for a more complex command line[footnote:
the command backfillsbackfill unused memory unused memory with 
0x12 and the overall 16 bit sum of the complete 64 kByte block is 
zero. If the program counter on an mcs51 runs wild the backfill 
pattern 0x12 will be interpreted as an lcall to address 0x1212 
(where an emergency routine could sit).
] could look like:

srec_cat sourcefile.ihx -intel  -fill 0x12 0x0000 0xfffe 
-little-endian-checksum-negative 0xfffe 0x02 0x02  -o 
sourcefile.hex -intel

The srecord package is available at http://sourceforge.net/projects/srecord/
.

3.2.3 Projects with Multiple Source Files

SDCC can compile only ONE file at a time. Let us for example 
assume that you have a project containing the following files:

foo1.c (contains some functions)
foo2.c (contains some more functions)
foomain.c (contains more functions and the function main)

The first two files will need to be compiled separately with the 
commands:

sdcc -c foo1.c
sdcc -c foo2.c

Then compile the source file containing the main() function and 
linkLinker the files together with the following command:

sdcc foomain.c foo1.rel foo2.rel<file>.rel

Alternatively, foomain.c can be separately compiled as well:

sdcc -c foomain.c
sdcc foomain.rel foo1.rel foo2.rel

The file containing the main() function must be the first file 
specified in the command line, since the linkage editor processes 
file in the order they are presented to it. The linker is invoked 
from SDCC using a script file with extension .lnk<file>.lnk. You 
can view this file to troubleshoot linking problems such as those 
arising from missing libraries.

3.2.4 Projects with Additional LibrariesLibraries

Some reusable routines may be compiled into a library, see the 
documentation for the assembler and linkage editor (which are in 
<installdir>/share/sdcc/doc) for how to create a .lib<file>.lib 
library file. Section [subsec:Using-sdar-to] below contains a 
minimal example. Libraries created in this manner can be included 
in the command line. Make sure you include the -L <library-path> 
option to tell the linker where to look for these files if they 
are not in the current directory. Here is an example, assuming 
you have the source file foomain.c and a library foolib.lib in 
the directory mylib (if that is not the same as your current 
project):

sdcc foomain.c foolib.lib -L mylib

Note here that mylib must be an absolute path name.

The most efficient way to use libraries is to keep separate 
modules in separate source files. The lib file now should name 
all the modules.rel<file>.rel files. For an example see the 
standard library file libsdcc.lib in the directory 
<installdir>/share/lib/small.

3.2.5 Using sdar to Create and Manage Librariessdar<subsec:Using-sdar-to>

Support for sdar format libraries was introduced in SDCC 2.9.0.

Both the GNU and BSD ar format variants are supported by sdld 
linkers.

To create a library containing sdas object files, you should use 
the following sequence:


sdar -rc <library name>.lib <list of .rel files>

3.3 Command Line OptionsCommand Line Options<sec:Command-Line-Options>

3.3.1 Processor Selection OptionsOptions processor selectionProcessor selection options

-mmcs51-mmcs51 Generate code for the Intel MCS51MCS51 family of 
processors. This is the default processor target.

-mds390-mds390 Generate code for the Dallas DS80C390DS80C390 
processor.

-mds400-mds400 Generate code for the Dallas DS80C400DS80C400 
processor.

-mhc08-mhc08 Generate code for the Freescale/Motorola HC08 (aka 
68HC08) HC08 family of processors.

-ms08-ms08 Generate code for the Freescale/Motorola S08 (aka 
68HCS08, HCS08, CS08) S08 family of processors.

-mz80-mz80 Generate code for the Zilog Z80Z80 family of 
processors.

-mz180-mz180 Generate code for the Zilog Z180Z180 family of 
processors.

-mr2k-mr2k Generate code for the Rabbit 2000 / Rabbit 3000 family 
of processors.

-mr3ka-mr3ka Generate code for the Rabbit 3000A family of 
processors.

-msm83-msm83 Generate code for the Sharp SM83sm83 (GameBoy Z80) 
processor.

-mtlcs90-mtlcs90 Generate code for the Toshiba TLCS-90 processor.

-mez80_z80-mez80_z80 Generate code for the Zilog eZ80 processor 
in Z80 mode.

-mstm8-mstm8 Generate code for the STMicroelectronics STM8 family 
of processors.

-mpdk13-mpdk13 Generate code for Padauk processors with 13 bit 
wide program memory.

-mpdk14-mpdk14 Generate code for Padauk processors with 14 bit 
wide program memory.

-mpdk15-mpdk15 Generate code for Padauk processors with 15 bit 
wide program memory.

-mpic14-mpic14 Generate code for the Microchip PIC 14PIC14-bit 
processors (p16f84 and variants. In development, not complete).



-mpic16-mpic16 Generate code for the Microchip PIC 16PIC16-bit 
processors (p18f452 and variants. In development, not complete).

SDCC inspects the program name it was called with so the 
processor family can also be selected by renaming the sdcc binary 
(to f.e. z80-sdcc) or by calling SDCC from a suitable link. 
Option -m has higher priority than setting from program name.

3.3.2 Preprocessor OptionsOptions preprocessorPreprocessor!Options
  sdcpp (preprocessor)

SDCC uses sdcpp, an adapted version of the GNU Compiler 
Collectiongcc (GNU Compiler Collection) preprocessor cppcpp|seesdcpp
 (gcc http://gcc.gnu.org/). If you need more dedicated options 
than those listed below please refer to the GCC CPP Manual at http://www.gnu.org/software/gcc/onlinedocs/
.

-I<path>-I<path> The additional location where the preprocessor 
will look for <..h> or “..h” files.

-D<macro[=value]>-D<macro[=value]> Command line definition of 
macros. Passed to the preprocessor.

-M-M Tell the preprocessor to output a rule suitable for make 
describing the dependencies of each object file. For each source 
file, the preprocessor outputs one make-rule whose target is the 
object file name for that source file and whose dependencies are 
all the files `#include'd in it. This rule may be a single line 
or may be continued with `\'-newline if it is long. The list of 
rules is printed on standard output instead of the preprocessed C 
program. `-M' implies `-E-E'.

-C-C Tell the preprocessor not to discard comments. Used with the 
`-E' option.

-MM-MM Like `-M' but the output mentions only the user header 
files included with `#include “file"'. System header files 
included with `#include <file>' are omitted.

-Aquestion(answer)-Aquestion(answer) Assert the answer answer for 
question, in case it is tested with a preprocessor conditional 
such as `#if #question(answer)'. `-A-' disables the standard 
assertions that normally describe the target machine.

-Umacro-Umacro Undefine macro macro. `-U' options are evaluated 
after all `-D' options, but before any `-include' and `-imacros' 
options.

-dM-dM Tell the preprocessor to output only a list of the macro 
definitions that are in effect at the end of preprocessing. Used 
with the `-E' option.

-dD-dD Tell the preprocessor to pass all macro definitions into 
the output, in their proper sequence in the rest of the output.

-dN-dN Like `-dD' except that the macro arguments and contents 
are omitted. Only `#define name' is included in the output.

-Wp preprocessorOption[,preprocessorOption]-Wp preprocessorOption[,preprocessorOption]
... Pass the preprocessorOption to the preprocessor sdcppsdcpp (preprocessor)
. 

3.3.3 Optimization OptionsOptions optimizationOptimization options

--nogcse--nogcse Will not do global common subexpression 
elimination, this option may be used when the compiler creates 
undesirably large stack/data spaces to store compiler temporaries 
(spill locations, slocsloc (spill location)). A warning message 
will be generated when this happens and the compiler will 
indicate the number of extra bytes it allocated. It is 
recommended that this option NOT be used, #pragma nogcsepragma nogcse
 can be used to turn off global subexpression eliminationSubexpression elimination
 for a given function only.

--noinvariant--noinvariant Will not do loop invariant 
optimizations, this may be turned off for reasons explained for 
the previous option. For more details of loop optimizations 
performed see Loop Invariants in section [subsec:Loop-Optimizations]
. It is recommended that this option NOT be used, #pragma 
noinvariantpragma noinvariant can be used to turn off invariant 
optimizations for a given function only.

--noinduction--noinduction Will not do loop induction 
optimizations, see section strength reduction for more details. 
It is recommended that this option is NOT used, #pragma 
noinductionpragma noinduction can be used to turn off induction 
optimizations for a given function only.

--noloopreverse--noloopreverse Will not do loop reversal Loop reversing
optimization.

--nolabelopt --nolabelopt Will not optimize labels (makes the 
dumpfiles more readable).

--no-xinit-opt--no-xinit-opt Will not memcpy initialized data 
from code space into xdata space. This saves a few bytes in code 
space if you don't have initialized dataVariable initialization.

--nooverlay--nooverlay  The compiler will not overlay parameters 
and local variables of any function, see section Parameters and 
local variables for more details.

--no-peep--no-peep Disable peep-hole optimization with built-in 
rules.

--peep-file--peep-file <filename> This option can be used to use 
additional rules to be used by the peep hole optimizer. See 
section [subsec:Peephole-Optimizer] Peep Hole optimizations for 
details on how to write these rules.

--peep-asm--peep-asm Pass the inline assembler code through the 
peep hole optimizer. This can cause unexpected changes to inline 
assembler code, please go through the peephole optimizerPeephole optimizer
 rules defined in the source file tree '<target>/peeph.def' 
before using this option.

--peep-return--peep-return Let the peep hole optimizer do return 
optimizations. This is the default without --debug--debug.

--no-peep-return--no-peep-return Do not let the peep hole 
optimizer do return optimizations. This is the default with -
-debug--debug.

--opt-code-speed--opt-code-speed The compiler will optimize code 
generation towards fast code, possibly at the expense of code 
size.

--opt-code-size--opt-code-size The compiler will optimize code 
generation towards compact code, possibly at the expense of code 
speed.

--fomit-frame-pointer--fomit-frame-pointer Frame pointer will be 
omitted when the function uses no local variables. On the 
z80-related ports this option will result in the frame pointer 
always being omitted.

--max-allocs-per-node--max-allocs-per-node Setting this to a high 
value will result in increased compilation time (and increased 
memory use during compilation) and more optimized code being 
generated. Setting it to lower values speeds up compilation, but 
does not optimize as much. The default value is 3000. This option 
currently does not affect the mcs51, ds390, pic14 and pic16 
ports.

--nolospre--nolospre Disable lospre. lospre is an advanced 
redundancy elimination technique, essentially an improved variant 
of global subexpression elimination.

--allow-unsafe-read--allow-unsafe-read Allow optimizations to 
generate unsafe reads. This will enable additional optimizations, 
but can result in spurious reads from undefined memory addresses, 
which can be harmful if the target system uses certain ways of 
doing memory-mapped I/O.

--nostdlibcall--nostdlibcall Disable the optimization of calls to 
the standard library.

3.3.4 Other OptionsOptions other

-v --version--version-v displays the sdcc version.

-c --compile-only--compile-only-c will compile and assemble the 
source, but will not call the linkage editor.

--c1mode--c1mode reads the preprocessed source from standard 
input and compiles it. The file name for the assembler output 
must be specified using the -o option.

-E-E Run only the C preprocessorPreprocessor. Preprocess all the 
C source files specified and output the results to standard 
output.

-o <path/file>-o <path/file> The output path where everything 
will be placed or the file name used for all generated output 
files. If the parameter is a path, it must have a trailing slash 
(or backslash for the Windows binaries) to be recognized as a 
path. Note for Windows users: if the path contains spaces, it 
should be surrounded by quotes. The trailing backslash should be 
doubled in order to prevent escaping the final quote, for 
example: -o ”F:\Projects\test3\output 1\\” or put after the final 
quote, for example: -o ”F:\Projects\test3\output 1”\. The path 
using slashes for directory delimiters can be used too, for 
example: -o ”F:/Projects/test3/output 1/”.

-x <type>-x <type> The specified type overrides the file type 
that SDCC detected based on the file name extension. The 
currently supported options are ”c”, ”c-header” and ”none”. The 
option ”none” restores the default behavior.

--stack-auto--stack-auto All functions in the source file will be 
compiled as reentrantreentrant, i.e. the parameters and local 
variables will be allocated on the stackstack. See section [sec:Parameters-and-Local-Variables]
 Parameters and Local Variables for more details. If this option 
is used all source files in the project should be compiled with 
this option. It automatically implies --int-long-reent and -
-float-reent. 

--callee-saves--callee-saves <lyx:--callee-saves-function1[,function2][,function3]...>
function1[,function2][,function3].... The compiler by default 
uses a caller saves convention for register saving across 
function calls, however this can cause unnecessary register 
pushing and popping when calling small functions from larger 
functions. This option can be used to switch the register saving 
convention for the function names specified. The compiler will 
not save registers when calling these functions, no extra code 
will be generated at the entry and exit (function prologuefunction prologue
 and epiloguefunction epilogue) for these functions to save and 
restore the registers used by these functions, this can 
SUBSTANTIALLY reduce code and improve run time performance of the 
generated code. In the future the compiler (with inter procedural 
analysis) will be able to determine the appropriate scheme to use 
for each function call. DO NOT use this option for built-in 
functions such as _mulint..., if this option is used for a 
library function the appropriate library function needs to be 
recompiled with the same option. If the project consists of 
multiple source files then all the source file should be compiled 
with the same --callee-saves option string. Also see #pragma 
callee_saves pragma calleesaves [ite:callee_saves-function1[,function2[,function3...]]--]
.

--all-callee-saves--all-callee-saves Function of --callee-saves 
will be applied to all functions by default.

--debug--debug When this option is used the compiler will 
generate debug information. By default, the debug information 
collected in a file with .cdb extension can be used with the 
SDCDB. For more information see documentation for SDCDB. Another 
file with a .omf extension contains debug information in AOMF or 
AOMF51AOMF, AOMF51 format which is commonly used by third party 
tools. When –out-gmt-elf is used, the debug information is in 
DWARF format instead.

-S-S Stop after the stage of compilation proper; do not assemble. 
The output is an assembler code file for the input file 
specified.

--int-long-reent--int-long-reent Integer (16 bit) and long (32 
bit) libraries have been compiled as reentrant. Note by default 
these libraries are compiled as non-reentrant. See section 
Installation for more details.

--cyclomatic--cyclomatic This option will cause the compiler to 
generate an information message for each function in the source 
file. The message contains some important information about the 
function. The number of edges and nodes the compiler detected in 
the control flow graph of the function, and most importantly the 
cyclomatic complexityCyclomatic complexity see section on 
Cyclomatic Complexity for more details.

--float-reent--float-reent Floating point library is compiled as 
reentrantreentrant. See section Installation for more details.

--fsigned-char--fsigned-char By default char is unsigned. To set 
the signedness for characters to signed, use the option -
-fsigned-char. If this option is set and no signedness keyword 
(unsigned/signed) is given, a char will be unsigned. All other 
types are unaffected.

--nostdinc--nostdinc This will prevent the compiler from passing 
on the default include path to the preprocessor.

--nostdlib--nostdlib This will prevent the compiler from passing 
on the default libraryLibraries path to the linker.

--verbose--verbose Shows the various actions the compiler is 
performing.

-V-V Shows the actual commands the compiler is executing.

--no-c-code-in-asm--no-c-code-in-asm Hides your ugly and 
inefficient c-code from the asm file, so you can always blame the 
compiler :)

--no-peep-comments--no-peep-comments Don't include peep-hole 
comments in the generated asm files even if --fverbose-asm option 
is specified.

--i-code-in-asm--i-code-in-asm Include i-codes in the asm file. 
Sounds like noise but is helpful for debugging the compiler 
itself.

--less-pedanticpedantic--less-pedantic<lyx:--less-pedantic> 
Disable some of the more pedantic warningsWarnings. For more 
details, see the less_pedantic pragma [ite:less_pedantic].

--disable-warning <nnnn>--disable-warning Disable specific 
warning with number <nnnn>.

--Werror--Werror Treat all warnings as errors.

--print-search-dirs--print-search-dirs Display the directories in 
the compiler's search path

--vc--vc Display errors and warnings using MSVC style, so you can 
use SDCC with the visual studio IDEIDE. With SDCC both offering a 
GCC-like (the default) and a MSVC-likeMSVC output style output 
style, integration into most programming editors should be 
straightforward.

--use-stdout--use-stdout Send errors and warnings to stdout 
instead of stderr.

-Wa asmOption[,asmOption]-Wa asmOption[,asmOption]... Pass the 
asmOption to the assemblerOptions assemblerAssembler options. See 
file sdcc/sdas/doc/asmlnk.txt for assembler options.cd

--std-<arg> Determine the language standard. For enhanced 
compatibility with other compilers, --std can also be used with a 
single dash (i.e. -std) and with = or ␣ (whitespace) as 
delimiter. The language standard, specified via <arg>, can be one 
of the following:

  c89 --std-c89 Follow the ANSI C89 / ISO C90 standard. 
  Alternative spellings: c90, iso9899:1990

  c95 --std-sdcc99 Follow the ISO C90 standard as modified in 
  amendment 1. Alternative spelling: iso9899:199409

  c99 --std-sdcc99 Follow the ISO C99 standard. Alternative 
  spelling: iso9899:1999

  c11 --std-sdcc11 Follow the ISO C11 standard. Alternative 
  spelling: iso9899:2011

  c17 --std-sdcc17 Follow the ISO C17 standard. Alternative 
  spellings: iso9899:2017, c18, iso9899:2018

  c2x --std-sdcc2x Follow the ISO C2X standard. Alternative 
  spelling: c23

  sdcc89 --std-sdcc89 Generally follow the ANSI C89 / ISO C90 
  standard, but allow some SDCC behaviour that conflicts with the 
  standard. Alternative spelling: sdcc90

  sdcc99 --std-sdcc99 Generally follow the ISO C99 standard, but 
  allow some SDCC behaviour that conflicts with the standard.

  sdcc11 --std-sdcc11 Generally follow the ISO C11 standard, but 
  allow some SDCC behaviour that conflicts with the standard 
  (default).

  sdcc17 --std-sdcc17 Generally follow the ISO C17 standard, but 
  allow some SDCC behaviour that conflicts with the standard. 
  Alternative spelling: sdcc18

  sdcc2x --std-sdcc2x Generally follow the ISO C2X standard, but 
  allow some SDCC behaviour that conflicts with the standard. 
  Alternative spelling: sdcc23

--codeseg--codeseg <Value><lyx:-codeseg> <Name> The name to be 
used for the codecode segment, default CSEG. This is useful if 
you need to tell the compiler to put the code in a special 
segment so you can later on tell the linker to put this segment 
in a special place in memory. Can be used for instance when using 
bank switching to put the code in a bank.

--constseg--constseg <Value> <Name> The name to be used for the 
constconst segment, default CONST. This is useful if you need to 
tell the compiler to put the const data in a special segment so 
you can later on tell the linker to put this segment in a special 
place in memory. Can be used for instance when using bank 
switching to put the const data in a bank.

--fdollars-in-identifiers--fdollars-in-identifiers Permit '$' as 
an identifier character.

--more-pedantic--more-pedanticpedantic Actually this is not a 
SDCC compiler option but if you want more warnings you can use a 
separate tool dedicated to syntax checking like splint<lyx:more-pedantic-SPLINT>
lint (syntax checking tool) http://www.splint.org. To make your 
source files parseable by splint you will have to include lint.hsplint (syntax checking tool)
 in your source file and add brackets around extended keywords 
(like ”__at (0xab)” and ”__interrupt (2)”). 
Splint has an excellent on line manual at http://www.splint.org/manual/
 and it's capabilities go beyond pure syntax checking. You'll 
need to tell splint the location of SDCC's include files so a 
typical command line could look like this: 
splint -I /usr/local/share/sdcc/include/mcs51/  myprogram.c

--use-non-free--use-non-free<lyx:--use-non-free> Search / include 
non-free licensed libraries and header files, located under the 
non-free directory - see section [subsec:Search-Paths]

3.3.5 Linker OptionsOptions linkerLinker options

--lib-path--lib-path <path> <absolute path to additional 
libraries> This option is passed to the linkage editor's 
additional librariesLibraries search path. The path name must be 
absolute. Additional library files may be specified in the 
command line. See section Compiling programs for more details.

-L -L <path> <absolute path to additional libraries> Same as 
above.

--xram-loc--xram-loc <Value> <Value> The start location of the 
external ramxdata (mcs51, ds390 named address space), default 
value is 0. The value entered can be in Hexadecimal or Decimal 
format, e.g.: --xram-loc 0x8000 or --xram-loc 32768.

--code-loc--code-loc <Value> <Value> The start location of the 
codecode segment, default value 0. Note when this option is used 
the interrupt vector tableinterrupt vector table is also 
relocated to the given address. The value entered can be in 
Hexadecimal or Decimal format, e.g.: --code-loc 0x8000 or -
-code-loc 32768.

--stack-loc--stack-loc <Value> <Value> The value entered can be 
in Hexadecimal or Decimal format, e.g. --stack-loc 0x20 or -
-stack-loc 32.

  For stm8, by default the stack is placed at the device-specific 
  reset value. By using this option, the stack can be placed 
  anywhere in the lower 16-bits of the stm8 memory space. This is 
  particularly useful for working around the stack roll-over 
  antifeature present in some stm8 devices.

--xstack-loc--xstack-loc <Value> <Value> By default the external 
stackxstack is placed after the __pdatapdata (mcs51, ds390 named address space)
 segment. Using this option the xstack can be placed anywhere in 
the external memory space of the 8051. The value entered can be 
in Hexadecimal or Decimal format, e.g. --xstack-loc 0x8000 or -
-xstack-loc 32768. The provided value should not overlap any 
other memory areas such as the pdata or xdata segment and with 
enough space for the current application.

--data-loc--data-loc <Value> <Value> The start location of the 
internal ram datadata (mcs51, ds390 named address space) segment. 
The value entered can be in Hexadecimal or Decimal format, eg. -
-data-loc 0x20 or --data-loc 32. (By default, the start location 
of the internal ram data segment  is set as low as possible in 
memory, taking into account the used register banks and the bit 
segment at address 0x20. For example if register banks 0 and 1 
are used without bit variables, the data segment will be set, if 
--data-loc is not used, to location 0x10.)

--idata-loc--idata-loc <Value> <Value> The start location of the 
indirectly addressable internal ramidata (mcs51, ds390 named address space)
 of the 8051, default value is 0x80. The value entered can be in 
Hexadecimal or Decimal format, eg. --idata-loc 0x88 or -
-idata-loc 136.

--bit-loc <Value> The start location of the bitbit addressable 
internal ram of the 8051. This is not implemented yet. Instead an 
option can be passed directly to the linker: -Wl -bBSEG=<Value>.

--out-fmt-ihx--out-fmt-ihx The linker output (final object code) 
is in Intel Hex format.Intel hex format This is the default 
option. The format itself is documented in the documentation of 
srecordsrecord (bin, hex, ... tool).

--out-fmt-s19--out-fmt-s19 The linker output (final object code) 
is in Motorola S19 formatMotorola S19 format. The format itself 
is documented in the documentation of srecord.

--out-fmt-elf--out-fmt-s19HC08!Options!--out-fmt-elf The linker 
output (final object code) is in ELF formatELF format. (Currently 
only supported for the HC08HC08, S08 and STM8 processors). When 
used with –debug, the debug info is in DWARF format instead of 
CDB.

-Wl linkOption[,linkOption]-Wl linkOption[,linkOption]<lyx:-Wl option>
... Pass the linkOption to the linker. If a bootloader is used an 
option like ”-Wl -bCSEG=0x1000” would be typical to set the start 
of the code segment. Either use the double quotes around this 
option or use no space (e.g. -Wl-bCSEG=0x1000). See also #pragma 
constseg and #pragma codeseg in section[sec:Pragmas]. File 
sdcc/sdas/doc/asmlnk.txt has more on linker options.

3.3.6 MCS51 OptionsOptions MCS51MCS51 options

--model-small--model-small Generate code for Small model 
programs, see section Memory Models for more details. This is the 
default model.

--model-medium--model-medium Generate code for Medium model 
programs, see section Memory Models for more details. If this 
option is used all source files in the project have to be 
compiled with this option. It must also be used when invoking the 
linker.

--model-large--model-large Generate code for Large model 
programs, see section Memory Models for more details. If this 
option is used all source files in the project have to be 
compiled with this option. It must also be used when invoking the 
linker.

--model-huge--model-huge Generate code for Huge model programs, 
see section Memory Models for more details. If this option is 
used all source files in the project have to be compiled with 
this option. It must also be used when invoking the linker.

--xstack--xstack Uses a pseudo stack in the __pdatapdata (mcs51, ds390 named address space)
 area (usually the first 256 bytes in the external ram) for 
allocating variables and passing parameters. See section [subsec:External-Stack]
  External Stack for more details.

--iram-size <Value>--iram-size <Value> Causes the linker to check 
if the internal ram usage is within limits of the given value.

--xram-size <Value>--xram-size <Value> Causes the linker to check 
if the external ram usage is within limits of the given value.

--code-size <Value>--code-size <Value> Causes the linker to check 
if the code memory usage is within limits of the given value.

--stack-size <Value>--stack-size <Value> Causes the linker to 
check if there is at minimum <Value> bytes for stack.

--acall-ajmp --acall-ajmp Replaces the three byte instructions 
lcall/ljmp with the two byte instructions acall/ajmp. Only use 
this option if your code is in the same 2k block of memory. You 
may need to use this option for some 8051 derivatives which lack 
the lcall/ljmp instructions.

--no-ret-without-call --no-ret-without-call Causes the code 
generator to insert an extra lcall or acall instruction whenever 
it needs to use a ret instruction in a context other than a 
function returning. This option is needed when using the InfineonInfineon
 XC800 series microcontrollers to keep its Memory Extension Stack 
balanced.

3.3.7 DS390 / DS400 OptionsOptions DS390DS390

--model-flat24DS390!Options!--model-flat24 Generate 24-bit flat 
mode code. This is the one and only that the ds390 code generator 
supports right now and is default when using -mds390. See section 
Memory Models for more details.

--protect-sp-updateDS390!Options!--protect-sp-update disable 
interrupts during ESP:SP updates.

--stack-10bitDS390!Options!--stack-10bit Generate code for the 10 
bit stack mode of the Dallas DS80C390 part. This is the one and 
only that the ds390 code generator supports right now and is 
default when using -mds390. In this mode, the stack is located in 
the lower 1K of the internal RAM, which is mapped to 0x400000. 
Note that the support is incomplete, since it still uses a single 
byte as the stack pointer. This means that only the lower 256 
bytes of the potential 1K stack space will actually be used. 
However, this does allow you to reclaim the precious 256 bytes of 
low RAM for use for the DATA and IDATA segments. The compiler 
will not generate any code to put the processor into 10 bit stack 
mode. It is important to ensure that the processor is in this 
mode before calling any re-entrant functions compiled with this 
option. In principle, this should work with the --stack-auto--stack-auto
 option, but that has not been tested. It is incompatible with 
the --xstack--xstack option. It also only makes sense if the 
processor is in 24 bit contiguous addressing mode (see the -
-model-flat24 option).

--stack-probeDS390!Options!--stack-probe insert call to function 
__stack_probe at each function prologue.

--tini-libidDS390!Options!--tini-libid <nnnn> LibraryID used in 
-mTININative. 

--use-acceleratorDS390!Options!--use-accelerator generate code 
for DS390 Arithmetic Accelerator. 

3.3.8 Options common to all z80-related ports (z80, z180, r2k, 
  r3ka, sm83, tlcs90, ez80_z80)

--no-std-crt0Z80!Options!--no-std-crt0 When linking, skip the 
standard crt0.rel object file. You must provide your own crt0.rel 
for your system when linking.

--callee-saves-bcZ80!Options!--callee-saves-bc Force a called 
function to always save BC.

--codeseg <Value>Z80!Options!--codeseg <Value> Use <Value> for 
the code segment name.

--constseg <Value>Z80!Options!--constseg <Value> Use <Value> for 
the const segment name.

3.3.9 Z80 OptionsOptions Z80Z80 (apply to z80, z180, r2k, r3ka, 
  tlcs90, ez80_z80)

--portmode=<Value>Z80!Options!--portmode=<Value> Determinate PORT 
I/O mode (<Value> is z80 or z180).

--asm=<Value>Z80!Options!--asm=<Value> Define assembler name 
(<Value> is rgbds, sdasz80, isas or z80asm).

--reserve-regs-iyZ80!Options!--reserve-regs-iy This option tells 
the compiler that it is not allowed to use register pair iy. The 
option can be useful for systems where iy is reserved for the OS. 
This option is incompatible with --fomit-frame-pointer.

--fno-omit-frame-pointerZ80!Options!--fno-omit-frame-pointer 
Never omit the frame pointer.

3.3.10 SM83 OptionsOptions GBZ80SM83

-bo <Num>GBZ80!Options!-bo <Num> Use code bank <Num>.

-ba <Num>GBZ80!Options!-ba <Num> Use data bank <Num>.

3.3.11 STM8 OptionsOptions STM8STM8 options

--model-medium--model-medium Generate code for Medium model 
programs, see section Memory Models for more details. This is the 
default model.

--model-large--model-large Generate code for Large model 
programs, see section Memory Models for more details. If this 
option is used all source files in the project have to be 
compiled with this option. It must also be used when invoking the 
linker.

3.3.12 Intermediate Dump Options<subsec:Intermediate-Dump-Options>
  Options intermediate dumpIntermediate dump options

The following options are provided for the purpose of 
retargetting and debugging the compiler. They provide a means to 
dump the intermediate code (iCodeiCode) generated by the compiler 
in human readable form at various stages of the compilation 
process. More on iCodes see chapter [subsec:The-anatomy-of] ”The 
anatomy of the compiler”.

--dum-ast--dump-ast This option will cause the compiler to dump 
the abstract syntax tree to the econsole.

--dump-i-code--dump-i-code Will dump iCodes at various stages 
into files named <source filename>.dump<stage>.

--dump-graphs--dump-graphs Will dump internal representations as 
graphviz .dot files. Depending on other options, this can include 
the control-flow graph at lospre, insertion of bank selection 
instructions or register allocation and the conflict graph and 
tree-decomposition at register allocation.

--fverbose-asm--no-gen-comments Include code generator and 
peep-hole comments in the generated asm files.

3.3.13 Redirecting output on Windows Shells

By default SDCC writes its error messages to ”standard error”. To 
force all messages to ”standard output” use --use-stdout--use-stdout
. Additionally, if you happen to have visual studio installed in 
your windows machine, you can use it to compile your sources 
using a custom build and the SDCC --vc--vc option. Something like 
this should work:

c:\sdcc\bin\sdcc.exe --vc --model-large -c $(InputPath)

3.4 Environment variablesEnvironment variables

SDCC recognizes the following environment variables:

SDCC_LEAVE_SIGNALSSDCC!Environment variables!SDCCLEAVESIGNALS 
SDCC installs a signal handlersignal handler to be able to delete 
temporary files after an user break (^C) or an exception. If this 
environment variable is set, SDCC won't install the signal 
handler in order to be able to debug SDCC.

TMP, TEMP, TMPDIRSDCC!Environment variables!TMP, TEMP, TMPDIR 
Path, where temporary files will be created. The order of the 
variables is the search order. In a standard *nix environment 
these variables are not set, and there's no need to set them. On 
Windows it's recommended to set one of them.

SDCC_HOMESDCC!Environment variables!SDCCHOME Path, see section [subsec:Install-paths]
 ” Install Paths”.

SDCC_INCLUDESDCC!Environment variables!SDCCINCLUDE Path, see 
section [subsec:Search-Paths] ”Search Paths”.

SDCC_LIBSDCC!Environment variables!SDCCLIB Path, see section [subsec:Search-Paths]
 ”Search Paths”..

There are some more environment variables recognized by SDCC, but 
these are mainly used for debugging purposes. They can change or 
disappear very quickly, and won't be documented[footnote:
if you are curious search in SDCC's sources for ”getenv”
]SDCC!Environment variables!undocumented.

3.5 SDCC Language Extensions

SDCC supports some language extensions useful for embedded 
systems. These include named address spaces (see also section 5.1 
of the Embedded C standard). SDCC supports both intrinsic named 
address spaces (which ones are supported depends on the target 
architecture) and non-intrinsic named address spaces (defined by 
the user using the keyword __addressmod, they are particularly 
useful with custom bank-switching hardware). Unlike the Embedded 
C standard, SDCC allows local variables to have an intrinsic 
named address space even when not explicitly declared as static 
or extern. Depending on the target architecture, support can be 
limited to objects in such address spaces and exclude 
pointer-based access to those.

3.5.1 MCS51/DS390 intrinsic named address spaces

SDCC supports the following MCS51-specific intrinsic address 
spaces:

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/MCS51_named.svg>

3.5.1.1 __datadata (mcs51, ds390 named address space) / __nearnear (named address space)

This is the default (generic) address space for the Small Memory 
model. Variables in this address space will be allocated in the 
directly addressable portion of the internal RAM of a 8051, e.g.:

__data unsigned char test_data;

Writing 0x01 to this variable generates the assembly code:

75*00 01   mov  _test_data,#0x01

3.5.1.2 __xdataxdata (mcs51, ds390 named address space) / __farfar (named address space)

Variables in this address space will be placed in the external 
RAM. This is the default (generic) address space for the Large 
Memory model, e.g.:

__xdata unsigned char test_xdata;

Writing 0x01 to this variable generates the assembly code:

90s00r00   mov  dptr,#_test_xdata
74 01      mov  a,#0x01
F0         movx @dptr,a 

3.5.1.3 __idataidata (mcs51, ds390 named address space)

Variables in this address space will be allocated into the 
indirectly addressable portion of the internal ram of a 8051, 
e.g.:

__idata unsigned char test_idata;

Writing 0x01 to this variable generates the assembly code:

78r00       mov  r0,#_test_idata
76 01       mov  @r0,#0x01

Please note, the first 128 byte of idata physically access the 
same RAM as the data memory. The original 8051 had 128 byte idata 
memory, nowadays most devices have 256 byte idata memory. The 
stackstack is located in idata memory (unless --xstack is 
specified).

3.5.1.4 __pdatapdata (mcs51, ds390 named address space)

Paged xdata access is just as straightforward as using the other 
addressing modes of a 8051. It is typically located at the start 
of xdata and has a maximum size of 256 bytes. The following 
example writes 0x01 to the pdata variable. Please note, pdata 
access physically accesses xdata memory. The high byte of the 
address is determined by port P2 P2 (mcs51 sfr)(or in case of 
some 8051 variants by a separate Special Function Register, see 
section [subsec:MCS51-variants]). This is the default (generic) 
address space for the Medium Memory model, e.g.:

__pdata unsigned char test_pdata;

Writing 0x01 to this variable generates the assembly code:

78r00      mov r0,#_test_pdata
74 01      mov a,#0x01
F2         movx @r0,a

If the --xstack--xstack option is used the pdata memory area is 
followed by the xstack memory area and the sum of their sizes is 
limited to 256 bytes.

3.5.1.5 __codecode

'Variables' in this address space will be placed in the code 
memory:

__code unsigned char test_code;

Read access to this variable generates the assembly code:

90s00r6F   mov dptr,#_test_code
E4         clr a
93         movc a,@a+dptr 

char indexed arrays of characters in code memory can be accessed 
efficiently:

__code char test_array[] = {'c','h','e','a','p'}; 

Read access to this array using an 8-bit unsigned index generates 
the assembly code:

E5*00      mov a,_index 

90s00r41   mov dptr,#_test_array

93         movc a,@a+dptr 

3.5.1.6 __bitbit

This is a data-type and an address space. When a variable is 
declared as a bit, it is allocated into the bit addressable 
memory of 8051, e.g.:

__bit test_bit;

Writing 1 to this variable generates the assembly code:

D2*00       setb _test_bit

The bit addressable memory consists of 128 bits which are located 
from 0x20 to 0x2f in data memory.
Apart from this 8051 specific intrinsic named address space most 
architectures support ANSI-C bit-fieldsbit-fields[footnote:
Not really meant as examples, but nevertheless showing what 
bit-fields are about: device/include/mc68hc908qy.h and 
support/regression/tests/bitfields.c
]. In accordance with ISO/IEC 9899 bits and bitfields without an 
explicit signed modifier are implemented as unsigned.

3.5.1.7 __sfrsfr / __sfr16sfr16 / __sfr32sfr32 / __sbitsbit

Like the __bit keyword, __sfr / __sfr16 / __sfr32 / __sbit 
signify both a data-type and named address space, they are used 
to describe the special function registers and special __bit 
variables of a 8051, eg:

__sfr __atat (0x80) P0;  /* special function register P0 at 
location 0x80 */

/* 16 bit special function register combination for timer 0
   with the high byte at location 0x8C and the low byte at 
location 0x8A */
__sfr16 __at (0x8C8A) TMR0;

__sbit __atat (0xd7) CY;  /* CY (Carry FlagFlagsCarry flag) */

Special function registers which are located on an address 
dividable by 8 are bit-addressable, an __sbit addresses a 
specific bit within these sfr.
16 Bit and 32 bit special function register combinations which 
require a certain access order are better not declared using 
__sfr16 or __sfr32. Although SDCC usually accesses them Least 
Significant Byte (LSB) first, this is not guaranteed.


Please note, if you use a header file which was written for 
another compiler then the __sfr / __sfr16 / __sfr32 / __sbit 
intrinsic named address spaces will most likely be not 
compatible. Specifically the syntax  sfr P0 = 0x80;  is compiled 
without warning by SDCC to an assignment of 0x80 to a variable 
called P0. Nevertheless with the file compiler.hcompiler.h (include file)
 it is possible to write header filesHeader filesInclude files 
which can be shared among different compilers (see section [sec:Porting-code-to-other-compilers]
). 

3.5.1.8 PointersPointer to MCS51/DS390 intrinsic named address 
  spaces

SDCC allows (via language extensions) pointers to explicitly 
point to any of the named address spacesMemory model of the 8051. 
In addition to the explicit pointers, the compiler uses (by 
default) generic pointers which can be used to point to any of 
the memory spaces.

Pointer declaration examples:

/* pointer physically in internal ram pointing to object in 
external ram */
__xdata unsigned char * __data p;

/* pointer physically in external ram pointing to object in 
internal ram */
__data unsigned char * __xdata p;

/* pointer physically in code rom pointing to data in xdata space 
*/
__xdata unsigned char * __code p;

/* pointer physically in code space pointing to data in code 
space */
__code unsigned char * __code p;

/* generic pointer physically located in xdata space */
unsigned char * __xdata p;

/* generic pointer physically located in default memory space */
unsigned char * p;

/* the following is a function pointerfunction pointer physically 
located in data space */
char (* __data fp)(void);

Well you get the idea.

All unqualified pointers are treated as 3-byte (4-byte for the 
ds390) generic pointers.

The highest order byte of the generic pointers contains the data 
space information. Assembler support routines are called whenever 
data is stored or retrieved using generic pointers. These are 
useful for developing reusable libraryLibraries routines. 
Explicitly specifying the pointerPointer type will generate the 
most efficient code.

3.5.1.9 Notes on MCS51 memoryMCS51 memory layout

The 8051 family of microcontrollers have a minimum of 128 bytes 
of internal RAM memory which is structured as follows:

- Bytes 00-1F - 32 bytes to hold up to 4 banks of the registers 
R0 to R7,
- Bytes 20-2F - 16 bytes to hold 128 bitbit variables and,
- Bytes 30-7F - 80 bytes for general purpose use.


Additionally some members of the MCS51 family may have up to 128 
bytes of additional, indirectly addressable, internal RAM memory 
(__idataidata (mcs51, ds390 named address space)). Furthermore, 
some chips may have some built in external memory (__xdataxdata (mcs51, ds390 named address space)
) which should not be confused with the internal, directly 
addressable RAM memory (__datadata (mcs51, ds390 named address space)
). Sometimes this built in __xdata memory has to be activated 
before using it (you can probably find this information on the 
datasheet of the microcontroller your are using, see also section 
[subsec:MCS51-Startup-Code] Startup-Code).

Normally SDCC will only use the first bankregister bank (mcs51, ds390)
 of registers (register bank 0), but it is possible to specify 
that other banks of registers (keyword __using using (mcs51, ds390 register bank)
) should be used for example in interruptinterruptinterrupt 
routines. By default, the compiler will place the stack after the 
last byte of allocated memory for variables. For example, if the 
first 2 banks of registers are used, and only four bytes are used 
for data variables, it will position the base of the internal 
stack at address 20 (0x14). This implies that as the stackstack 
grows, it will use up the remaining register banks, and the 16 
bytes used by the 128 bit variables, and 80 bytes for general 
purpose use. If any bit variables are used, the data variables 
will be placed in unused register banks and after the byte 
holding the last bit variable. For example, if register banks 0 
and 1 are used, and there are 9 bit variables (two bytes used), 
data variables will be placed starting from address 0x10 to 0x20 
and continue at address 0x22. You can also use --data-loc--data-loc <Value>
 to specify the start address of the data and --iram-size--iram-size <Value>
 to specify the size of the total internal RAM (data+idata). 


By default the 8051 linker will place the stack after the last 
byte of (i)data variables. Option --stack-loc--stack-loc <Value> 
allows you to specify the start of the stack, i.e. you could 
start it after any data in the general purpose area. If your 
microcontroller has additional indirectly addressable internal 
RAM (idata) you can place the stack on it. You may also need to 
use --xdata-loc--xdata-loc<Value> to set the start address of the 
external RAM (xdata) and --xram-size--xram-size <Value> to 
specify its size. Same goes for the code memory, using --code-loc--code-loc <Value>
 and --code-size--code-size <Value>. If in doubt, don't specify 
any options and see if the resulting memory layout is 
appropriate, then you can adjust it.

The linker generates two files with memory allocation 
information. The first, with extension .map<file>.map shows all 
the variables and segments. The second with extension .mem<file>.mem
 shows the final memory layout. The linker will complain either 
if memory segments overlap, there is not enough memory, or there 
is not enough space for stack. If you get any linking warnings 
and/or errors related to stack or segments allocation, take a 
look at either the .map or .mem files to find out what the 
problem is. The .mem file may even suggest a solution to the 
problem.

3.5.2 Z80/Z180/eZ80 intrinsic named address spaces

3.5.2.1 __sfrsfr (in/out to 8-bit addresses)

The Z80Z80 family has separate address spaces for memory and 
input/output memory. I/O memoryI/O memory (Z80, Z180)Z80!I/O memory
Z180!I/O memory is accessed with special instructions, e.g.:

__sfr __at(0x78) IoPort;  /* define a var in I/O space at 78h 
called IoPort */ 

Writing 0x01 to this variable generates the assembly code:

3E 01      ld a,#0x01
D3 78      out (_IoPort),a 

3.5.2.2 __banked __sfrsfr (in/out to 16-bit addresses)

The keyword __banked is used to support 16 bit addresses in I/O 
memory e.g.:

__sfr __banked __atat(0x123) IoPort; 

Writing 0x01 to this variable generates the assembly code:

01 23 01   ld bc,#_IoPort
3E 01      ld a,#0x01
ED 79      out (c),a 

3.5.2.3 __sfrsfr (in0/out0 to 8 bit addresses on Z180Z180/HD64180HD64180 (see Z180)
  )

The compiler option --portmodeZ180!Options!--portmode=180 (80) 
and a compiler #pragma portmodeZ180!Pragmas!pragma portmode z180 
(z80) is used to turn on (off) the Z180/HD64180 port addressing 
instructions in0/out0 instead of in/out. If you include the file 
z180.h this will be set automatically.

3.5.3 SM83 intrinsic named address spaces

3.5.3.1 __sfrsfr

The keyword __sfr is an alternative way to access memory 
locations 0xff00 to 0xffff, which are typically used for 
memory-mapped I/O e.g.:

__sfr __atat(0xff01) IoPort; 

3.5.4 HC08/S08 intrinsic named address spaces

3.5.4.1 __datadata (hc08 named address space) 

Variables int the address space __data resides in the first 256 
bytes of memory (the direct page). The HC08HC08 is most efficient 
at accessing variables (especially pointers) stored here.

3.5.4.2 __xdataxdata (hc08 named address space) 

Variables in the address space__xdata can reside anywhere in 
memory. This is the default (generic address space).

3.5.5 PDK14/PDK15 intrinsic named address spaces

3.5.5.1 __sfrsfr

The Padauk family has separate address spaces for memory and 
input/output memory. I/O memory is accessed with special 
instructions, e.g.:

__sfr __at(0x18) gpcc;  /* define a var in I/O space at 18h 
called gpcc */

3.5.5.2 __sfr16sfr16

The Padauk family has a 16-bit timer accessed with special 
instructions.

3.5.6 Non-intrinsic named address spacesNon-intrinsic named address spaces

SDCC supports user-defined non-intrinsic named address spaces. So 
far SDCC only supports them for bank-switching. You need to have 
a function that switches to the desired memory bank and declare a 
corresponding named address space:

void setb0(void); // The function that sets the currently active 
memory bank to b0
void setb1(void); // The function that sets the currently active 
memory bank to b1
__addressmodaddressmod setb0 spaceb0; // Declare a named address 
space called spaceb0 that uses setb0()
__addressmod setb1 spaceb1; // Declare a named address space 
called spaceb1 that uses setb1()
spaceb0 int x; // An int in address space spaceb0
spaceb1 int *y; // A pointer to an int in address space spaceb1
spaceb0 int *spaceb1 z; // A pointer in address space spaceb1 
that points to an int in address space spaceb0

Non-intrinsic named address spaces for data in ROM are declared 
using the const keyword:

void setb0(void); // The function that sets the currently active 
memory bank to b0
void setb1(void); // The function that sets the currently active 
memory bank to b1
__addressmodaddressmod setb0 const spaceb0; // Declare a named 
address space called spaceb0 that uses setb0() and resides in ROM
__addressmod setb1 spaceb1; // Declare a named address space 
called spaceb1 that uses setb1() and resides in RAM
const spaceb0 int x = 42; // An int in address space spaceb0
spaceb1 int *y; // A pointer to an int in address space spaceb1
const spaceb0 int *spaceb1 z; // A pointer in address space 
spaceb1 that points to a constant int in address space spaceb0

Variables in non-intrinsic named address spaces will be placed in 
areas of the same name (this can be used for the placement of 
named address spaces in memory by the linker).

SDCC will automatically insert calls to the corresponding 
function before accessing the variable. SDCC inserts the minimum 
possible number calls to the bank selection functions. See 
Philipp Klaus Krause, ”Optimal Placement of Bank Selection 
Instructions in Polynomial Time” for details on how this works.

3.5.7 Absolute AddressingAbsolute addressing

Data items can be assigned an absolute address with the __atat 
<address> keyword (the address needs to be either a parenthesized 
constant expression or a constant), which can also be used in 
addition to a named address space, e.g.:

__xdata unsigned int __at (0x7ffe) chksum;

In the above example the variable chksum will be located at 
0x7ffe and 0x7fff of the external ram. The compiler does not 
reserve any space for variables declared in this way[margin:
 !
] (they are implemented with an equate in the assembler). Thus it 
is left to the programmer to make sure there are no overlaps with 
other variables that are declared without the absolute address. 
The assembler listing file (.lst<file>.lst) and the linker output 
files (.rst<file>.rst) and (.map<file>.map) are good places to 
look for such overlaps.

If however you provide an initializerVariable initialization 
actual memory allocation will take place and overlaps will be 
detected by the linker. E.g.:

__code char __at (0x7ff0) Id[5] = ”SDCC”;

In the above example the variable Id will be located from 0x7ff0 
to 0x7ff4 in code memory.

In case of memory mapped I/O devices the keyword volatile has to 
be used to tell the compiler that accesses might not be removed:

volatilevolatile __xdataxdata (mcs51, ds390 named address space) 
unsigned char __atat (0x8000) PORTA_8255;

For some architectures (mcs51) array accesses are more efficient 
if an (xdata/far) arrayAligned array starts at a block (256 byte) 
boundaryblock boundary (section [subsec:A-Step-by Assembler Introduction]
 has an example).
Absolute addresses can be specified for variables in all named 
address spaces, e.g.:

__bitbit __atat (0x02) bvar;

The above example will allocate the variable at offset 0x02 in 
the bit-addressable space. There is no real advantage to 
assigning absolute addresses to variables in this manner, unless 
you want strict control over all the variables allocated. One 
possible use would be to write hardware portable code. For 
example, if you have a routine that uses one or more of the 
microcontroller I/O pins, and such pins are different for two 
different hardwares, you can declare the I/O pins in your routine 
using:

extern volatilevolatile __bit MOSI;    /* master out, slave in */
extern volatile __bit MISO;    /* master in, slave out */
extern volatile __bit MCLK;    /* master clock */

/* Input and Output of a byte on a 3-wire serial bus.
   If needed adapt polarity of clock, polarity of data and bit 
order
 */
unsigned char spi_io(unsigned char out_byte)
{ 
    unsigned char i=8;
    do { 
        MOSI = out_byte & 0x80;
        out_byte <<= 1;
        MCLK = 1;
        /* __asm nop __endasm; */        /* for slow peripherals 
*/
        if(MISO)
            out_byte += 1;
        MCLK = 0;
    } while(--i);
    return out_byte;
}

Then, someplace in the code for the first hardware you would use

__bit __atat (0x80) MOSI;    /* I/O port 0, bit 0 */
__bit __at (0x81) MISO;    /* I/O port 0, bit 1 */
__bit __at (0x82) MCLK;    /* I/O port 0, bit 2 */

Similarly, for the second hardware you would use

__bit __at (0x83) MOSI;    /* I/O port 0, bit 3 */
__bit __at (0x91) MISO;    /* I/O port 1, bit 1 */
__bitbit __at (0x92) MCLK;    /* I/O port 1, bit 2 */

and you can use the same hardware dependent routine without 
changes, as for example in a library. This is somehow similar to 
sbit, but only one absolute address has to be specified in the 
whole project.

3.5.8 __sdcc_external_startupsdccexternalstartup

When a function unsigned char __sdcc_external_startup(void) is 
present, it is executed before both the initialization of static 
and global variables, as well as main. This allows to implement 
functionality that needs to be done early. For example: disabling 
a hardware watchdog that would otherwise bite during the time it 
takes to initialize global variables; setup or calibration of 
system/peripheral clocks; or, a memory check that needs to be 
done before any memory (other than the return address for __sdcc_external_startup
 itself) is in use.

If this routine returns a non-zero value, the static and global 
variable initialization will be skipped and the function main 
will be invoked. Otherwise static and global variables will be 
initialized before the function main is invoked.

For mos6502, z80, z80n, z180, sm83, ez80_z80, tlcs90, r2k, r2ka, 
r3ka, when using a custom crt0, support depends on the custom 
crt0.

3.5.9 Preserved register specification

SDCC allows to specify preserved registers in function 
declarations, to enable further optimizations on calls to 
functions implemented in assembler. Example for the Z80 
architecture specifying that a function will preserve register 
pairs bc and iy:

void f(void) __preserves_regs(b, c, iyl, iyh);

3.5.10 Binary constantsBinary constants

SDCC supports the use of C23 binary constants, such as 0b01100010 
when the compiler is invoked using --std-sdccxx, even when the 
corresponding --std-cxx, does not. Note: xx is a placeholder for 
the desired version of the C standard.

3.5.11 Returning void

SDCC allows functions to return expressions of type void. This 
feature is only enabled when the compiler is invoked using --std-sdccxx
. Note: xx is a placeholder for the desired version of the C 
standard.

3.5.12 Omitting promotion on arguments of vararg function (does 
  not apply to pdk13, pdk14, pdk15)

Arguments to vararg functions are not promoted when explicitly 
cast. This feature is only enabled when the compiler is invoked 
using --std-sdccxx. This breaks compability with the C standards, 
so linking code compiled with --std-sdccxx with code compiled 
using --std-cxx can result in failing programs when arguments to 
vararg functions are explicitly cast. Note: xx is a placeholder 
for the desired version of the C standard.

3.6 ParametersParametersfunction parameter and Local Variableslocal variables
  <sec:Parameters-and-Local-Variables>

Automatic (local) variables and parameters to functions are 
placed on the stack for most targets. For 
MCS51/DS390/HC08/S08/PDK13/PDK14/PDK15 they can either be placed 
on the stack or in data-space. The default action of the compiler 
is to place these variables in the internal RAM (for small model) 
or external RAM (for medium or large model). This in fact makes 
them similar to staticstatic so by default functions are 
non-reentrantreentrant. 

They can be placed on the stackstack by using the --stack-auto--stack-auto
 option, by using #pragma stackautopragma stackauto or by using 
the __reentrantreentrant keyword in the function declaration, 
e.g.:

unsigned char foo(char i) __reentrant
{ 
    ... 
}

Since stack space on 8051 is limited, and accessing the stack is 
slow for the Padauk, the __reentrant keyword or the --stack-auto 
option should be used sparingly. Note that the __reentrant 
keyword just means that the parameters & local variables will be 
allocated to the stack, it does not mean that the function is 
register bankregister bank (mcs51, ds390) independent.

Local variableslocal variables can be assigned intrinsic named 
address spaces and absoluteAbsolute addressing addresses, e.g.: 

unsigned char foo(__xdata int parm)
{
    __xdata unsigned char i;
    __bit bvar;
    __data unsigned char __atat (0x31) j;
    ... 
}

In the above example the parameterfunction parameter parm and the 
variable i will be allocated in the external ram, bvar in bit 
addressable space and j in internal ram. When compiled with -
-stack-auto or when a function is declared as reentrant this 
should only be done for static variables.

It is however allowed to use bit parameters in reentrant 
functions and also non-static local bit variables are supported. 
Efficient use is limited to 8 semi-bitregisters in bit space. 
They are pushed and popped to stackstack as a single byte just 
like the normal registers.

3.7 Overlaying<subsec:Overlaying>Overlaying

For non-reentrantreentrant functions SDCC will try to reduce 
internal ram space usage by overlaying parameters and local 
variables of a function (if possible). Parameters and local 
variableslocal variables of a function will be allocated to an 
overlayable segment if the function has no other function calls 
and the function is non-reentrant and the memory modelMemory model
 is small. If an explicit intrinsic named address spaceintrinsic named address space
 is specified for a local variable, it will NOT be overlaid.

Note that the compiler (not the linkage editor) makes the 
decision for overlaying the data items. Functions that are called 
from an interrupt service routine[margin:
!
] should be preceded by a #pragma nooverlaypragma nooverlay if 
they are not reentrant.

Also note that the compiler does not do any processing of inline 
assembler code, so the compiler might incorrectly assign local 
variables and parameters of a function into the overlay segment 
if the inline assembler code calls other c-functions that might 
use the overlay. In that case the #pragma nooverlay should be 
used.

Parameters and local variables of functions that contain 16 or 32 
bit multiplicationMultiplication or divisionDivision will NOT be 
overlaid since these are implemented using external functions, 
e.g.:

#pragma save
#pragma nooverlaypragma nooverlay
void set_error(unsigned char errcd)
{
    P3 = errcd;
} 
#pragma restore

void some_isr () __interruptinterrupt (2)
{
    ...
    set_error(10);
    ...
}

In the above example the parameter errcd for the function 
set_error would be assigned to the overlayable segment if the 
#pragma nooverlay was not present, this could cause unpredictable 
runtime behaviour when called from an interrupt service routine. 
The #pragma nooverlay ensures that the parameters and local 
variables for the function are NOT overlaid.

3.8 Interrupt Service Routines<subsec:Interrupt-Service-Routines>

3.8.1 General Information

SDCC allows interrupt service routines to be coded in C, with 
some extended keywords.

void timer_isr (void) __interrupt (1) __using (1)
{
    ...
}

The optional number following the __interruptinterruptinterrupt 
keyword is the interrupt number this routine will service. When 
present, the compiler will insert a call to this routine in the 
interrupt vector tableinterrupt vector table for the interrupt 
number specified. If you have multiple source files in your 
project, interrupt service routines can be present in any of 
them, but a prototype of the isr MUST be present or included in 
the file that contains the function main. The optional (8051 
specific) keyword __usingusing (mcs51, ds390 register bank) can 
be used to tell the compiler to use the specified register bank 
when generating code for this function.
Interrupt service routines open the door for some very 
interesting bugs:

3.8.1.1 <subsec:Common-interrupt-pitfall-volatile>Common 
  interrupt pitfall: variable not declared volatile

If an interrupt service routine changes variables which are 
accessed by other functions these variables have to be declared 
volatilevolatile. See http://en.wikipedia.org/wiki/Volatile_variable
.

3.8.1.2 <subsec:Common-interrupt-pitfall-non-atomic>Common 
  interrupt pitfall: non-atomic access

If the access to these variables is not atomicatomic (i.e. the 
processor needs more than one instruction for the access and 
could be interrupted while accessing the variable) the interrupt 
must be disabled during the access to avoid inconsistent data. 
Access to 16 or 32 bit variables is obviously not atomic on 8 bit 
CPUs and should be protected by disabling interrupts. You're not 
automatically on the safe side if you use 8 bit variables though. 
We need an example here: f.e. on the 8051 the harmless looking ”
flags |= 0x80;” is not atomic if flags resides in xdata. Setting ”
flags |= 0x40;” from within an interrupt routine might get lost 
if the interrupt occurs at the wrong time. ”counter += 8;” is not 
atomic on the 8051 even if counter is located in data memory.
Bugs like these are hard to reproduce and can cause a lot of 
trouble. 

3.8.1.3 <subsec:Common-interrupt-pitfall-stack-overflow>Common 
  interrupt pitfall: stack overflow

The return address and the registers used in the interrupt 
service routine are saved on the stackstack so there must be 
sufficient stack space. If there isn't variables or registers (or 
even the return address itself) will be corrupted. This stack 
overflowstack overflow is most likely to happen if the interrupt 
occurs during the ”deepest” subroutine when the stack is already 
in use for f.e. many return addresses.

3.8.1.4 <subsec:Common-interrupt-pitfall-non-reentrant>Common 
  interrupt pitfall: use of non-reentrant functions

A special note here, integer multiplicative operators and 
floating-pointFloating point support operations might be 
implemented using external support routines, depending on the 
target architecture. If an interrupt service routine needs to do 
any of these operations on a target where functions are 
non-reentrant by default, then the support routines (as mentioned 
in a following section) will have to be recompiled using the -
-stack-auto--stack-auto option and the source file will need to 
be compiled using the --int-long-reent--int-long-reent compiler 
option. 
Note, the type promotiontype promotion required by ANSI C can 
cause 16 bit routines to be used[margin:
 !
] without the programmer being aware of it. See f.e. the cast 
(unsigned char)(tail-1) within the if clause in section [subsec:A-Step-by Assembler Introduction]
.

Calling other functions from an interrupt service routine on a 
target where functions are non-reentrant by default is not 
recommended, avoid it if possible. Note that when some function 
is called from an interrupt service routine it should be preceded 
by a #pragma nooverlaypragma nooverlay if it is not reentrant. 
Furthermore non-reentrant functions should not be called from the 
main program while the interrupt service routine might be active. 
They also must not be called from low priority interrupt service 
routines while a high priority interrupt service routine might be 
active. You could use semaphores or make the function critical if 
all parameters are passed in registers.
 Also see section [subsec:Overlaying] about Overlaying and 
section [subsec:Functions-using-private-banks] about Functions 
using private register banks.

3.8.2 MCS51/DS390 Interrupt Service Routines

Interruptinterrupt numbers and the corresponding address & 
descriptions for the Standard 8051/8052 are listed below. SDCC 
will automatically adjust the interrupt vector table to the 
maximum interrupt number specified.




+--------------+-----------------+----------------+
| Interrupt #  | Description     | Vector Address |
+--------------+-----------------+----------------+
+--------------+-----------------+----------------+
|      0       | External 0      | 0x0003         |
+--------------+-----------------+----------------+
|      1       | Timer 0         | 0x000b         |
+--------------+-----------------+----------------+
|      2       | External 1      | 0x0013         |
+--------------+-----------------+----------------+
|      3       | Timer 1         | 0x001b         |
+--------------+-----------------+----------------+
|      4       | Serial          | 0x0023         |
+--------------+-----------------+----------------+
|      5       | Timer 2 (8052)  | 0x002b         |
+--------------+-----------------+----------------+
|     ...      |                 | ...            |
+--------------+-----------------+----------------+
|      n       |                 | 0x0003 + 8*n   |
+--------------+-----------------+----------------+



If the interrupt service routine is defined without __usingusing (mcs51, ds390 register bank)
using (mcs51, ds390 register bank) a register bank or with 
register bank 0 (__using (0)), the compiler will save the 
registers used by itself on the stack upon entry and restore them 
at exit, however if such an interrupt service routine calls 
another function then the entire register bank will be saved on 
the stack. This scheme may be advantageous for small interrupt 
service routines which have low register usage.

If the interrupt service routine is defined to be using a 
specific register bank then only a, b, dptr & psw are saved and 
restored, if such an interrupt service routine calls another 
function (using another register bank) then the entire register 
bank of the called function will be saved on the stackstack. This 
scheme is recommended for larger interrupt service routines.

3.8.3 HC08HC08 Interrupt Service Routines

Since the number of interruptsHC08!interrupt available is chip 
specific and the interrupt vector table always ends at the last 
byte of memory, the interrupt numbers corresponds to the 
interrupt vectors in reverse order of address. For example, 
interrupt 1 will use the interrupt vector at 0xfffc, interrupt 2 
will use the interrupt vector at 0xfffa, and so on. However, 
interrupt 0 (the reset vector at 0xfffe) is not redefinable in 
this way; instead see section [subsec:MCS51-Startup-Code] for 
details on customizing startup.

3.8.4 Z80, Z180 and eZ80 Interrupt Service Routines

The Z80Z80 uses several different methods for determining the 
correct interruptZ80!interrupt vector depending on the hardware 
implementation. Therefore, SDCC does not attempt to generate an 
interrupt vector table.

By default, SDCC generates code for a maskable interrupt, which 
uses a RETI instruction to return from the interrupt. To write an 
interrupt handler for the non-maskable interrupt, which needs a 
RETN instruction instead, leave out the interrupt number:

void nmi_isr (void) __critical __interrupt
{
    ...
}

Since interrupts on the Z80 and Z180 are level-triggered (except 
for the NMI), interruptible interrupt handlers should only be 
used where hardware acknowledge is available.


+--------------------------------------+-----------------------------------------+------------------------------------------------------------+
| Type                                 | Syntax                                  | Behaviour                                                  |
+--------------------------------------+-----------------------------------------+------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+------------------------------------------------------------+
| Interruptible interrupt handler      | void f(void) __interrupt                | Interrupt handler can be interrupted by further interrupts |
                                                                                 +------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+------------------------------------------------------------+
| Non-interruptible interrupt handler  | void f(void) __critical __interrupt(0)  | Interrupt handler can be interrupted by NMI only           |
+--------------------------------------+-----------------------------------------+------------------------------------------------------------+
| NMI handler                          | void f(void) __critical __interrupt     | Interrupt handler can be interrupted by NMI only           |
+--------------------------------------+-----------------------------------------+------------------------------------------------------------+


3.8.5 Rabbit 2000, 3000 and 3000A Interrupt Service Routines

SDCC does not attempt to generate an interrupt vector table.


+--------------------------------------+-----------------------------------------+------------------------------------------------------------------------------+
| Type                                 | Syntax                                  | Behaviour                                                                    |
+--------------------------------------+-----------------------------------------+------------------------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+------------------------------------------------------------------------------+
| Interruptible interrupt handler      | void f(void) __interrupt                | Interrupt handler can be interrupted by further interrupts of 
same priority |
                                                                                 +------------------------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+------------------------------------------------------------------------------+
| Non-interruptible interrupt handler  | void f(void) __critical __interrupt(0)  | Interrupt handler can be interrupted by interrupts of higher 
priority only  |
+--------------------------------------+-----------------------------------------+------------------------------------------------------------------------------+


3.8.6 SM83 and TLCS-90 Interrupt Service Routines

SDCC does not attempt to generate an interrupt vector table.


+--------------------------------------+-----------------------------------------+---------------------------------------------------------------+
| Type                                 | Syntax                                  | Behaviour                                                     |
+--------------------------------------+-----------------------------------------+---------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+---------------------------------------------------------------+
| Interruptible interrupt handler      | void f(void) __interrupt                | Interrupt handler can be interrupted by further interrupts    |
                                                                                 +---------------------------------------------------------------+
+--------------------------------------+-----------------------------------------+---------------------------------------------------------------+
| Non-interruptible interrupt handler  | void f(void) __critical __interrupt(0)  | Interrupt handler cannot be interrupted by further interrupts |
+--------------------------------------+-----------------------------------------+---------------------------------------------------------------+


3.8.7 STM8 Interrupt Service Routines

The STM8 interrupt table contains 31 entries: Reset (used by SDCC 
for program startup), trap and user interrupts 0 to 29. Where the 
keyword __interruptinterrupt is used for normal user interrupts, 
the __trap keyword is used for the trap handler:

void handler (void) __trap
{
    ...
}

3.9 Enabling and Disabling Interrupts

3.9.1 Critical Functions and Critical Statements

A special keyword may be associated with a block or a function 
declaring it as __critical. SDCC will generate code to disable 
all interruptsinterrupt upon entry to a critical function and 
restore the interrupt enable to the previous state before 
returning (for architectures where there is no efficient way to 
do so (sm83, tlcs90, stm8), interrupts will be unconditionally 
enabled instead). Nesting critical functions will need one 
additional byte on the stackstack for each call.

int foo () __criticalcriticalcritical
{
    ...
    ...
}

The critical attribute maybe used with other attributes like 
reentrant.
The keyword __critical may also be used to disable interrupts 
more locally:

__critical{ i++; }

More than one statement could have been included in the block.

3.9.2 Enabling and Disabling Interrupts directly

Interruptsinterrupt can also be disabled and enabled directly 
(8051):

EA = 0;            or:           EA_SAVE = EA;

...                              EA = 0;

EA = 1;                          ...

                                 EA = EA_SAVE;

On other architectures which have separate opcodes for enabling 
and disabling interrupts you might want to make use of defines 
with inline assemblyAssembler routines (HC08HC08!interrupt):

#define CLI __asmasm  cli  __endasmendasm; 

#define SEI __asm  sei  __endasm; 

or for SDCC version 3.2.0 or newer:

#define CLI asm (”cli”); 

#define SEI asm (”sei”); 

Note: it is sometimes sufficient to disable only a specific 
interrupt source like f.e. a timer or serial interrupt by 
manipulating an interrupt maskinterrupt mask register. 

Usually the time during which interrupts are disabled should be 
kept as short as possible. This minimizes both interrupt latencyinterrupt latency
 (the time between the occurrence of the interrupt and the 
execution of the first code in the interrupt routine) and 
interrupt jitterinterrupt jitter (the difference between the 
shortest and the longest interrupt latency). These really are 
something different, f.e. a serial interrupt has to be served 
before its buffer overruns so it cares for the maximum interrupt 
latency, whereas it does not care about jitter. On a loudspeaker 
driven via a digital to analog converter which is fed by an 
interrupt a latency of a few milliseconds might be tolerable, 
whereas a much smaller jitter will be very audible.

You can re-enable interrupts within an interrupt routine and on 
some architectures you can make use of two (or more) levels of 
interrupt prioritiesinterrupt priority. On some architectures 
which don't support interrupt priorities these can be implemented 
by manipulating the interrupt mask and re-enabling interrupts 
within the interrupt routine. Check there is sufficient space on 
the stackstack and don't add complexity unless you have to. 

3.9.3 Semaphoresemaphore locking (mcs51/ds390)

Some architectures (mcs51/ds390) have an atomicatomic bit test 
and clear instruction. These type of instructions are typically 
used in preemptive multitasking systems, where a routine f.e. 
claims the use of a data structure ('acquires a locklock on it'), 
makes some modifications and then releases the lock when the data 
structure is consistent again. The instruction may also be used 
if interrupt and non-interrupt code have to compete for a 
resource. With the atomic bit test and clear instruction 
interruptsinterrupt don't have to be disabled for the locking 
operation. 

SDCC generates this instruction if the source follows this 
pattern:

volatilevolatile bit resource_is_free;

if (resource_is_free)
  {
    resource_is_free=0;
    ...
    resource_is_free=1;
  } 

Note, mcs51 and ds390 support only an atomicatomic bit test and 
clear instruction (as opposed to atomic bit test and set).

3.10 Functions using private register banks<subsec:Functions-using-private-banks>
   (mcs51/ds390)

Some architectures have support for quickly changing register 
sets. SDCC supports this feature with the __usingusing (mcs51, ds390 register bank)
using (mcs51, ds390 register bank) attribute (which tells the 
compiler to use a register bankregister bank (mcs51, ds390) other 
than the default bank zero). It should only be applied to 
interruptinterrupt functions (see footnote below). This will in 
most circumstances make the generated ISR code more efficient 
since it will not have to save registers on the stack.

The __using attribute will have no effect on the generated code 
for a non-interrupt function (but may occasionally be useful 
anyway[footnote:
possible exception: if a function is called ONLY from 'interrupt' 
functions using a particular bank, it can be declared with the 
same 'using' attribute as the calling 'interrupt' functions. For 
instance, if you have several ISRs using bank one, and all of 
them call memcpy(), it might make sense to create a specialized 
version of memcpy() 'using 1', since this would prevent the ISR 
from having to save bank zero to the stack on entry and switch to 
bank zero before calling the function
]).
(pending: Note, nowadays the __using attribute has an effect on 
the generated code for a non-interrupt function.)

An interrupt function using a non-zero bank will assume that it 
can trash that register bank, and will not save it. Since 
high-priority interruptsinterruptsinterrupt priority can 
interrupt low-priority ones on the 8051 and friends, this means 
that if a high-priority ISR using a particular bank occurs while 
processing a low-priority ISR using the same bank, terrible and 
bad things can happen. To prevent this, no single register bank 
should be used by both a high priority and a low priority ISR. 
This is probably most easily done by having all high priority 
ISRs use one bank and all low priority ISRs use another. If you 
have an ISR which can change priority at runtime, you're on your 
own: I suggest using the default bank zero and taking the small 
performance hit.

It is most efficient if your ISR calls no other functions. If 
your ISR must call other functions, it is most efficient if those 
functions use the same bank as the ISR (see note 1 below); the 
next best is if the called functions use bank zero. It is very 
inefficient to call a function using a different, non-zero bank 
from an ISR. 

3.11 Inline Assembler Code<sec:Inline-Assembler-Code>Assembler routines

3.11.1 Inline Assembler Code Formats

SDCC supports two formats for inline assembler code definition:

3.11.1.1 Old __asm ... __endasm; Format

Most of inline assembler code examples in this manual use the old 
inline assembler code format, but the new format could be used 
equivalently.

Example:

__asm
    ; This is a comment
    label:
        nop
__endasm;

3.11.1.2 New __asm__ (”inline_assembler_code”) Format

The __asm__ inline assembler code format was introduced in SDCC 
version 3.2.0.

Example:

__asm__ (”; This is a comment\nlabel:\n\tnop”);

3.11.2 A Step by Step Introduction<subsec:A-Step-by Assembler Introduction>

Starting from a small snippet of c-code this example shows for 
the MCS51 how to use inline assembly, access variables, a 
function parameter and an array in xdata memory. The example uses 
an MCS51 here but is easily adapted for other architectures. This 
is a buffer routine which should be optimized:

unsigned char __farfar (named address space) __atat(0x7f00) 
buf[0x100];Aligned array
unsigned char head, tail;                 /* if interruptsinterrupt
 are involved see
                                             section [subsec:Common-interrupt-pitfall-volatile]
 about volatile */

void to_buffer( unsigned char c ) 
{
    if( head != (unsigned char)(tail-1) ) /* cast needed to avoid 
promotionpromotion to signed inttype promotion to integer */[margin:
 !
]
        buf[ head++ ] = c;                /* access to a 256 byte 
aligned array */
} 

If the code snippet (assume it is saved in buffer.c) is compiled 
with SDCC then a corresponding buffer.asm file is generated. We 
define a new function to_buffer_asm() in file buffer.c in which 
we cut and paste the generated code, removing unwanted comments 
and some ':'. Then add ”__asm” and ”__endasm;”[footnote:
Note, that the single underscore form (_asm and _endasm) are not 
C99 compatible, and for C99 compatibility, the double-underscore 
form (__asm and __endasm) has to be used. The latter is also used 
in the library functions.
] to the beginning and the end of the function body:

/* With a cut and paste from the .asm file, we have something to 
start with.
   The function is not yet OK! (registers aren't saved) */ 
void to_buffer_asm( unsigned char c ) 
{ 
    __asmasm
    mov  r2,dpl
;buffer.c if( head != (unsigned char)(tail-1) )  /* cast needed 
to avoid promotionpromotion to signed inttype promotion to 
integer */
    mov  a,_tail
    dec  a
    mov  r3,a
    mov  a,_head
    cjne a,ar3,00106$
    ret
00106$:
;buffer.c buf[ head++ ] = c; /* access to a 256 byte aligned 
array */Aligned array
    mov  r3,_head
    inc  _head
    mov  dpl,r3
    mov  dph,#(_buf >> 8)
    mov  a,r2
    movx @dptr,a
00103$:
    ret
    __endasmendasm;
} 

The new file buffer.c should compile with only one warning about 
the unreferenced function argument 'c'. Now we hand-optimize the 
assembly code and insert an #define USE_ASSEMBLY (1) and finally 
have:

unsigned char __far __at(0x7f00) buf[0x100];
unsigned char head, tail;
#define USE_ASSEMBLY (1)

#if !USE_ASSEMBLY

void to_buffer( unsigned char c )
{
    if( head != (unsigned char)(tail-1) )
        buf[ head++ ] = c;
}

#else

void to_buffer( unsigned char c )
{
    c; // to avoid warning: unreferenced function argument
    __asmasm
        ; save used registers here.
        ; If we were still using r2,r3 we would have to push them 
here.
; if( head != (unsigned char)(tail-1) )
        mov  a,_tail
        dec  a
        xrl  a,_head
        ; we could do an ANL a,#0x0f here to use a smaller buffer 
(see below)
        jz   t_b_end$
        ;
; buf[ head++ ] = c;
        mov  a,dpl        ; dpl holds lower byte of function 
argument
        mov  dpl,_head    ; buf is 0x100 byte aligned so head can 
be used directly
        mov  dph,#(_buf>>8)
        movx @dptr,a
        inc  _head
        ; we could do an ANL _head,#0x0f here to use a smaller 
buffer (see above)
t_b_end$:
        ; restore used registers here
    __endasmendasm;
}
#endif

The inline assembler code can contain any valid code understood 
by the assembler, this includes any assembler directives and 
comment lines. The assembler does not like some characters like 
':' or ''' in comments. You'll find an 100+ pages assembler 
manual in sdcc/sdas/doc/asmlnk.txtsdas (sdasgb, sdas6808, sdas8051, sdasz80)
Assembler documentation or online at http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/sdas/doc/asmlnk.txt
.

The compiler does not do any validation of the code within the 
__asmasm ... __endasmendasm; keyword pair. Specifically it will 
not know which registers are used and thus register 
pushing/poppingpush/pop has to be done manually. 

It is required that each assembly instruction be placed on a 
separate line. This is also recommended for labels (as the 
example shows). This is especially important to note when the 
inline assembler is placed in a C preprocessor macro as the 
preprocessor will normally put all replacing code on a single 
line. Only when the macro has each assembly instruction on a 
single line that ends with a line continuation character will it 
be placed as separate lines in the resulting .asm file.

#define DELAY   \
    __asm       \
        nop     \
        nop     \
    __endasm

When the --peep-asm--peep-asm command line option is used, the 
inline assembler code will be passed through the peephole 
optimizerPeephole optimizer. There are only a few (if any) cases 
where this option makes sense, it might cause some unexpected 
changes in the inline assembler code. Please go through the 
peephole optimizer rules defined in file peeph.def before using 
this option.

3.11.3 Naked Functions<subsec:Naked-Functions>Naked functions

A special keyword may be associated with a function declaring it 
as __nakednakednaked. The _naked function modifier attribute 
prevents the compiler from generating prologuefunction prologue 
and epiloguefunction epilogue code for that function. This means 
that the user is entirely responsible for such things as saving 
any registers that may need to be preserved, selecting the proper 
register bank, generating the return instruction at the end, etc. 
Practically, this means that the contents of the function must be 
written in inline assembler. This is particularly useful for 
interrupt functions, which can have a large (and often 
unnecessary) prologue/epilogue. For example, compare the code 
generated by these two functions:

volatilevolatile data unsigned char counter;

void simpleInterrupt(void) __interruptinterruptinterrupt (1)
{
    counter++;
}

void nakedInterrupt(void) __interrupt (2) __naked
{
    __asmasm
      inc     _counter ; does not change flags, no need to save 
psw
      reti    ; MUST explicitly include ret or reti in _naked 
function.
    __endasmendasm;
}

For an 8051 target, the generated simpleInterrupt looks like:

Note, this is an outdated example, recent versions of SDCC 
generate
the same code for simpleInterrupt() and nakedInterrupt()!

_simpleInterrupt:
    push    acc
    push    b
    push    dpl
    push    dph
    push    psw
    mov     psw,#0x00
    inc     _counter
    pop     psw
    pop     dph
    pop     dpl
    pop     b
    pop     acc
    reti

whereas nakedInterrupt looks like:

_nakedInterrupt:
    inc    _counter ; does not change flags, no need to save psw
    reti            ; MUST explicitly include ret or reti in 
_naked function

The related directive #pragma excludepragma exclude allows a more 
fine grained control over pushing & poppingpush/pop the 
registers.

While there is nothing preventing you from writing C code inside 
a _naked function, there are many ways to shoot yourself in the 
foot doing this, and it is recommended that you stick to inline 
assembler.

3.11.4 Use of Labels within Inline Assembler

SDCC allows the use of in-line assembler with a few restrictions 
regarding labels. All labels defined within inline assembler code 
have to be of the form nnnnn$ where nnnnn is a number less than 
100 (which implies a limit of utmost 100 inline assembler labels 
per function).[footnote:
This is a slightly more stringent rule than absolutely necessary, 
but stays always on the safe side. Labels in the form of nnnnn$ 
are local labels in the assembler, locality of which is confined 
within two labels of the standard form. The compiler uses the 
same form for labels within a function (but starting from 
nnnnn=00100); and places always a standard label at the beginning 
of a function, thus limiting the locality of labels within the 
scope of the function. So, if the inline assembler part would be 
embedded into C-code, an improperly placed non-local label in the 
assembler would break up the reference space for labels created 
by the compiler for the C-code, leading to an assembling error.

The numeric part of local labels does not need to have 5 digits 
(although this is the form of labels output by the compiler), any 
valid integer will do. Please refer to the assemblers 
documentation for further details.
] 

__asmasm
    mov     b,#10
00001$:
    djnz    b,00001$
__endasmendasm ;

Inline assembler code cannot reference any C-labels, however it 
can reference labelsLabels defined by the inline assembler, e.g.:

foo() {
    /* some c code */
    __asm
      ; some assembler code
      ljmp 0003$
    __endasm;
    /* some more c code */
clabel:  /* inline assembler cannot reference this label */ [footnote:
Here, the C-label clabel is translated by the compiler into a 
local label, so the locality of labels within the function is not 
broken.
]
    __asm
    0003$: ;label (can be referenced by inline assembler only)
    __endasmendasm ;
    /* some more c code */
}

In other words inline assembly code can access labels defined in 
inline assembly within the scope of the function. The same goes 
the other way, i.e. labels defines in inline assembly can not be 
accessed by C statements.

3.12 Support routines for integer multiplicative operators

Depending on the target architecture, some integer multiplicative 
operators might be implemented by support routines. These support 
routines exist in portable C versions to facilitate porting to 
other MCUs, although depending on the target, assembler routines 
might be used instead. The following files contain some of the 
described routines, all of them can be found in 
<installdir>/share/sdcc/lib.




+---------------+------------------------------------------+
| Function      | Description                              |
+---------------+------------------------------------------+
+---------------+------------------------------------------+
| _mulint.c     | 16 bit multiplication                    |
+---------------+------------------------------------------+
| _divsint.c    |  signed 16 bit division (calls _divuint) |
+---------------+------------------------------------------+
| _divuint.c    |  unsigned 16 bit division                |
+---------------+------------------------------------------+
| _modsint.c    | signed 16 bit modulus (calls _moduint)   |
+---------------+------------------------------------------+
| _moduint.c    | unsigned 16 bit modulus                  |
+---------------+------------------------------------------+
| _mullong.c    | 32 bit multiplication                    |
+---------------+------------------------------------------+
| _divslong.c   |  signed 32 division (calls _divulong)    |
+---------------+------------------------------------------+
| _divulong.c   | unsigned 32 division                     |
+---------------+------------------------------------------+
| _modslong.c   |  signed 32 bit modulus (calls _modulong) |
+---------------+------------------------------------------+
| _modulong.c   | unsigned 32 bit modulus                  |
+---------------+------------------------------------------+



In the mcs51, ds390, hc08, s08, pdk13, pdk14, pdk15, pic14 and 
pic16 backends they are by default compiled as non-reentrantreentrant
; when targeting on of these architectures, interruptinterrupt 
service routines should not do any of the above operations. If 
this is unavoidable then the above routines will need to be 
compiled with the --stack-auto--stack-auto option, after which 
the source program will have to be compiled with --int-long-reent--int-long-reent
 option. Notice that you don't have to call these routines 
directly. The compiler will use them automatically every time an 
integer operation is required.

3.13 Floating Point SupportFloating point support

SDCC supports (single precision 4 bytes) floating point numbers; 
the format is somewhat similar to IEEE, but it is not IEEE; in 
particular, denormalized floating -point numbers are not 
supported. The floating point support routines are derived from 
gcc's floatlib.c and consist of the following routines:




+------------------+----------------------------------------------+
| Function         | Description                                  |
+------------------+----------------------------------------------+
+------------------+----------------------------------------------+
| _fsadd.c         | add floating point numbers                   |
+------------------+----------------------------------------------+
| _fssub.c         | subtract floating point numbers              |
+------------------+----------------------------------------------+
| _fsdiv.c         | divide floating point numbers                |
+------------------+----------------------------------------------+
| _fsmul.c         | multiply floating point numbers              |
+------------------+----------------------------------------------+
| _fs2uchar.c      | convert floating point to unsigned char      |
+------------------+----------------------------------------------+
| _fs2schar.c      | convert floating point to signed char        |
+------------------+----------------------------------------------+
| _fs2uint.c       | convert floating point to unsigned int       |
+------------------+----------------------------------------------+
| _fs2sint.c       | convert floating point to signed int         |
+------------------+----------------------------------------------+
| _fs2ulong.c      | convert floating point to unsigned long      |
+------------------+----------------------------------------------+
| _fs2slong.c      | convert floating point to signed long        |
+------------------+----------------------------------------------+
| _uchar2fs.c      | convert unsigned char to floating point      |
+------------------+----------------------------------------------+
| _schar2fs.c      | convert signed char to floating point        |
+------------------+----------------------------------------------+
| _uint2fs.c       | convert unsigned int to floating point       |
+------------------+----------------------------------------------+
| _sint2fs.c       | convert signed int to floating point         |
+------------------+----------------------------------------------+
| _ulong2fs.c      | convert unsigned long to floating point      |
+------------------+----------------------------------------------+
| _slong2fs.c      | convert signed long to floating point        |
+------------------+----------------------------------------------+
| _ulonglong2fs.c  | convert unsigned long long to floating point |
+------------------+----------------------------------------------+
| _slonglong2fs.c  | convert singed long long to floating point   |
+------------------+----------------------------------------------+



3.14 Library RoutinesLibraries

<pending: this is messy and incomplete - a little more 
information is at 
http://sdcc.sourceforge.net/wiki/index.php/List_of_the_SDCC_library
>

3.14.1 Compiler support routines (_gptrget, _mulint etc.)

3.14.2 Stdclib functions (puts, printf, strcat etc.)

3.14.2.1 <stdio.h>

  getchar(), putchar()

<stdio.h>As usual on embedded systems you have to provide your 
own getchar()getchar() and putchar()putchar()printf()!putchar() 
routines. SDCC does not know whether the system connects to a 
serial line with or without handshake, LCD, keyboard or other 
device. And whether a lf to crlf conversion within putchar() is 
intended. You'll find examples for serial routines f.e. in 
sdcc/device/lib. For the mcs51 this minimalistic polling 
putchar() routine might be a start:

int putchar (int c) {
    while (!TI)    /* assumes UART is initialized */
        ;
    TI = 0;
    SBUF = c;

    return c;

}

  printf()

The default printf()printf() implementation in printf_large.c 
does not support floatFloating point support (except on ds390), 
only <NO FLOAT><NO FLOAT>printf()!floating point support will be 
printed instead of the value. To enable floating point output, 
recompile it with the option -DUSE_FLOATS=1USEFLOATS on the 
command line. Use --model-large--model-large for the mcs51 port, 
since this uses a lot of memory. To enable float support for the 
pic16 targets, see [subsec:pic16Libraries].

If you're short on code memory you might want to use 
printf_small()printf()!printfsmall() instead of printf(). For the 
mcs51 there additionally are assembly versions printf_tiny()printf()!printftiny() (mcs51)
 (subset of printf using less than 270 bytes) and printf_fast()printf()!printffast() (mcs51)
 and printf_fast_f()printf()!printffastf() (mcs51) 
(floating-point aware version of printf_fast) which should fit 
the requirements of many embedded systems (printf_fast() can be 
customized by unsetting #defines to not support long variables 
and field widths). Be sure to use only one of these printf 
options within a project.


Feature matrix of different printf options on mcs51.


+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| mcs51                                                                                                                                                                     | printfprintf()  | printf USE_FLOATS=1  |      printf_small        |  printf_fast    |                                        printf_fast_f                                        |                                           printf_tiny                                           |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| filename                                                                                                                                                                  | printf_large.c  |   printf_large.c     |        printfl.c         | printf_fast.c   |                                       printf_fast_f.c                                       |                                          printf_tiny.c                                          |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| ”Hello World” size

small / large                                                                                                                                         |  1.7k / 2.4k    |     4.3k / 5.6k      |       1.2k / 1.8k        |  1.3k / 1.3k    |                                         1.9k / 1.9k                                         |                                          0.44k / 0.44k                                          |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| code size

small / large                                                                                                                                                  |  1.4k / 2.0k    |     2.8k / 3.7k      | 0.45k / 0.47k (+ _ltoa)  |  1.2k / 1.2k    |                                         1.6k / 1.6k                                         |                                          0.26k / 0.26k                                          |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| formats                                                                                                                                                                   |    cdiopsux     |      cdfiopsux       |          cdosx           |     cdsux       |                                           cdfsux                                            |                                              cdsux                                              |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| long (32 bit) support                                                                                                                                                     |       x         |          x           |            x             |       x         |                                              x                                              |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| byte arguments on stack                                                                                                                                                   |       b         |          b           |            -             |       -         |                                              -                                              |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| float formatFloating point support                                                                                                                                        |       -         |         %f           |            -             |       -         | %f[footnote:
Range limited to +/- 4294967040, precision limited to 8 digits 
past decimal
] |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| float formats %e %g                                                                                                                                                       |       -         |          -           |            -             |       -         |                                              -                                              |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| field width                                                                                                                                                               |       x         |          x           |            -             |       x         |                                              x                                              |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| string speed[footnote:
Execution time of printf("%s%c%s%c%c%c", "Hello", ' ', "World", 
'!', '\r', '\n'); standard 8051 @ 22.1184 MHz, empty putchar()
],

small / large  | 1.52 / 2.59 ms  |   1.53 / 2.62 ms     |     0.92 / 0.93 ms       | 0.45 / 0.45 ms  |                                       0.46 / 0.46 ms                                        |                                          0.45 / 0.45 ms                                         |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| int speed[footnote:
Execution time of printf("%d", -12345); standard 8051 @ 22.1184 
MHz, empty putchar()
],

small / large                                               | 3.01 / 3.61 ms  |   3.01 / 3.61 ms     |     3.51 / 18.13 ms      | 0.22 / 0.22 ms  |                                       0.23 / 0.23 ms                                        |  0.25 / 0.25 ms[footnote:
printf_tiny integer speed is data dependent, worst case is 0.33 
ms
] |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| long speed[footnote:
Execution time of printf("%ld", -123456789); standard 8051 @ 
22.1184 MHz, empty putchar()
],

small / large                                         | 5.37 / 6.31 ms  |   5.37 / 6.31 ms     |     8.71 / 40.65 ms      | 0.40 / 0.40 ms  |                                       0.40 / 0.40 ms                                        |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+
| float speed[footnote:
Execution time of printf("%.3f", -12345.678); standard 8051 @ 
22.1184 MHz, empty putchar()
],

small / large                                       |       -         |   7.49 / 22.47 ms    |            -             |       -         |                                       1.04 / 1.04 ms                                        |                                                -                                                |
+---------------------------------------------------------------------------------------------------------------------------------------------------------------------------+-----------------+----------------------+--------------------------+-----------------+---------------------------------------------------------------------------------------------+-------------------------------------------------------------------------------------------------+


3.14.2.2 <malloc.h>malloc.h

As of SDCC 2.6.2 you no longer need to call an initialization 
routine before using dynamic memory allocationdynamic memory allocation (malloc)
 and a default heapheap (malloc) space of 1024 bytes is provided 
for malloc to allocate memory from. If you need a different heap 
size you need to recompile _heap.c with the required size defined 
in HEAP_SIZE. It is recommended to make a copy of this file into 
your project directory and compile it there with:

sdcc -c _heap.c -D HEAP_SIZE=2048

And then link it with:

sdcc main.rel _heap.rel

3.14.3 Math functions (sinf, powf, sqrtf etc.)

3.14.3.1 <math.h>

See definitions in file <math.h>.

3.14.4 Other libraries

LibrariesLibraries included in SDCC should have a license at 
least as liberal as the GPLv2+LEGPLv2+LE. Exception are pic 
device libraries and header files which are derived from 
Microchip header (.inc) and linker script (.lkr) files. Microchip 
requires that "The header files should state that they are only 
to be used with authentic Microchip devices" which makes them 
incompatible with GPL.

If you have ported some library or want to share experience about 
some code which f.e. falls into any of these categories Busses (I^{\textrm{2}}
C, CAN, Ethernet, Profibus, Modbus, USB, SPI, JTAG ...), Media 
(IDE, Memory cards, eeprom, flash...), En-/Decryption, Remote 
debugging, Realtime kernel, Keyboard, LCD, RTC, FPGA, PID then 
the sdcc-user mailing list http://sourceforge.net/p/sdcc/mailman/sdcc-user/
 would certainly like to hear about it.

Programmers coding for embedded systems are not especially famous 
for being enthusiastic, so don't expect a big hurray but as the 
mailing list is searchable these references are very valuable. 
Let's help to create a climate where information is shared.

3.15 Memory Models

3.15.1 MCS51 Memory ModelsMemory modelMCS51 memory model

3.15.1.1 Small, Medium, Large and Huge

SDCC allows four memory models for MCS51 code, small, medium, 
large and huge. Modules compiled with different memory models 
should never be combined together or the results would be 
unpredictable. The library routines supplied with the compiler 
are compiled for all models (however, the libraries for 
–stack-auto are compiled for the small and large models only). 
The compiled library modules are contained in separate 
directories as small, medium, large and huge so that you can link 
to the appropriate set.

When the medium, large or huge model is used all variables 
declared without specifying an intrinsic named address space will 
be allocated into the external ram, this includes all parameters 
and local variables (for non-reentrantreentrant functions). 
Medium model uses pdata and large and huge models use xdata. When 
the small model is used variables without an explicitly specified 
intrinsic named address space are allocated in the internal ram.

The huge model compiles all functions as banked[subsec:Bankswitching]
 and is otherwise equal to large for now. All other models 
compile the functions without bankswitching by default.

Judicious usage of the processor specific intrinsic named address 
spacesintrinsic named address space and the 'reentrant' function 
type will yield much more efficient code, than using the large 
model. Several optimizations are disabled when the program is 
compiled using the large model, it is therefore recommended that 
the small model be used unless absolutely required.

3.15.1.2 External Stack<subsec:External-Stack>stackExternal stack (mcs51)

The external stack (--xstack option--xstack) is located in pdatapdata (mcs51, ds390 named address space)
 memory (usually at the start of the external ram segment) and 
uses all unused space in pdata (max. 256 bytes). When --xstack 
option is used to compile the program, the parameters and local 
variableslocal variables of all reentrant functions are allocated 
in this area. This option is provided for programs with large 
stack space requirements. When used with the --stack-auto--stack-auto
 option, all parameters and local variables are allocated on the 
external stack (note: support libraries will need to be 
recompiled with the same options. There is a predefined target in 
the library makefile).

The compiler outputs the higher order address byte of the 
external ram segment into port P2P2 (mcs51 sfr) (see also section 
[subsec:MCS51-variants]), therefore when using the External Stack 
option, this port may not be used by the application program.

3.15.2 DS390 Memory ModelMemory modelDS390 memory model

The only model supported is Flat 24Flat 24 (DS390 memory model). 
This generates code for the 24 bit contiguous addressing mode of 
the Dallas DS80C390 part. In this mode, up to four meg of 
external RAM or code space can be directly addressed. See the 
data sheets at www.dalsemi.com for further information on this 
part.

Note that the compiler does not generate any code to place the 
processor into 24 bit mode (although tinibios in the ds390 
libraries will do that for you). If you don't use tinibiosTinibios (DS390)
, the boot loader or similar code must ensure that the processor 
is in 24 bit contiguous addressing mode before calling the SDCC 
startup code.

Like the --model-large option, variables will by default be 
placed into the XDATA segment.

Segments may be placed anywhere in the 4 meg address space using 
the usual --*-loc options. Note that if any segments are located 
above 64K, the -r flag must be passed to the linker to generate 
the proper segment relocations, and the Intel HEX output format 
must be used. The -r flag can be passed to the linker by using 
the option -Wl-r on the SDCC command line. However, currently the 
linker can not handle code segments > 64k.

3.15.3 STM8 Memory ModelsMemory modelSTM8 memory models

SDCC implements two memory models for the STM8: medium (default) 
and large. Modules compiled with different memory models should 
never be combined together. The library routines supplied with 
the compiler are compiled for all models.

In the medium model the address space is 16 bits for both objects 
and functions, allowing for a memory space of 64 KB. Since the 
STM8 typically has Flash starting at 0x8000, this means that only 
up to 32 KB of Flash can be used (most STM8 devices don't have 
more than 32 KB of Flash).

In the large memory model, the address space is 16 bits for 
objects and 24 bits for functions. Since the STM8 typically has 
flash starting at 0x8000, this means that up to 32 KB of flash 
can be used for constant data, while the whole Flash can be used 
for functions. Code generated for the large model is slightly 
bigger and slower and needs slightly more stack space than code 
generated for the medium model.

3.16 Pragmas<sec:Pragmas>Pragmas

Pragmas are used to turn on and/or off certain compiler options. 
Some of them are closely related to corresponding command-line 
options (see section [sec:Command-Line-Options]).
Pragmas should be placed before and/or after a function, placing 
pragmas inside a function body could have unpredictable results.

SDCC supports the following #pragma directives:

• savepragma save - this will save most current options to the 
  save/restore stack. See #pragma restore.

• restorepragma restore - will restore saved options from the 
  last save. saves & restores can be nested. SDCC uses a 
  save/restore stack: save pushes current options to the stack, 
  restore pulls current options from the stack. See #pragma save.


• callee_savespragma calleesavesfunction prologue 
  function1[,function2[,function3...]] <ite:callee_saves-function1[,function2[,function3...]]-->
  - The compiler by default uses a caller saves convention for 
  register saving across function calls, however this can cause 
  unnecessary register pushing and poppingpush/pop when calling 
  small functions from larger functions. This option can be used 
  to switch off the register saving convention for the function 
  names specified. The compiler will not save registers when 
  calling these functions, extra code need to be manually 
  inserted at the entry and exit for these functions to save and 
  restore the registers used by these functions, this can 
  SUBSTANTIALLY reduce code and improve run time performance of 
  the generated code. In the future the compiler (with inter 
  procedural analysis) may be able to determine the appropriate 
  scheme to use for each function call. If --callee-saves command 
  line option is used (see page [lyx:--callee-saves-function1[,function2][,function3]...]
  ), the function names specified in #pragma callee_savespragma calleesaves
   is appended to the list of functions specified in the command 
  line.

• excludepragma exclude none | {acc[,b[,dpl[,dph[,bits]]]]} - The 
  exclude pragma disables the generation of pairs of push/poppush/pop
   instructions in Interruptinterrupt Service Routines. The 
  directive should be placed immediately before the ISR function 
  definition and it affects ALL ISR functions following it. To 
  enable the normal register saving for ISR functions use #pragma 
  exclude nonepragma exclude. See also the related keyword 
  __nakednakednaked.

• less_pedanticpedanticpragma lesspedantic<ite:less_pedantic> - 
  the compiler will not warn you anymore for obvious mistakes, 
  you're on your own now ;-(. See also the command line option -
  -less-pedantic [lyx:--less-pedantic]. 
More specifically, the following warnings will be disabled: 
  comparison is always [true/false] due to limited range of data 
  type (94); overflow in implicit constant conversion (158); [the 
  (in)famous] conditional flow changed by optimizer: so said 
  EVELYN the modified DOG (110); function '[function name]' must 
  return value (59). 
Furthermore, warnings of less importance (of PEDANTIC and INFO 
  warning level) are disabled, too, namely: constant value '[]', 
  out of range (81); [left/right] shifting more than size of 
  object changed to zero (116); unreachable code (126); integer 
  overflow in expression (165); unmatched #pragma save and 
  #pragma restore (170); comparison of 'signed char' with 
  'unsigned char' requires promotion to int (185); ISO C90 does 
  not support flexible array members (187); extended stack by 
  [number] bytes for compiler temp(s) :in function '[function 
  name]': [] (114); function '[function name]', # edges [number] 
  , # nodes [number] , cyclomatic complexity [number] (121).

• disable_warning <nnnn>pragma disablewarning - the compiler will 
  not warn you anymore about warning number <nnnn>.

• nogcsepragma nogcse - will stop global common subexpression 
  elimination.

• noinductionpragma noinduction - will stop loop induction 
  optimizations.

• noinvariantpragma noinvariant - will not do loop invariant 
  optimizations. For more details see Loop Invariants in section[subsec:Loop-Optimizations]
  .

• noivpragma noiv - Do not generate interruptinterrupt vector 
  tableinterrupt vector table entries for all ISR functions 
  defined after the pragma. This is useful in cases where the 
  interrupt vector table must be defined manually, or when there 
  is a secondary, manually defined interrupt vector table (e.g. 
  for the autovector feature of the Cypress EZ-USB FX2). More 
  elegantly this can be achieved by omitting the optional 
  interrupt number after the __interrupt keyword, see section [subsec:Interrupt-Service-Routines]
   about interrupts.

• noloopreversepragma noloopreverse - Will not do loop reversal 
  optimization

• nooverlaypragma nooverlay - the compiler will not overlay the 
  parameters and local variables of a function.

• stackautopragma stackauto- See option --stack-auto--stack-auto 
  and section [sec:Parameters-and-Local-Variables] Parameters and 
  Local Variables.

• opt_code_speed pragma optcodespeed- The compiler will optimize 
  code generation towards fast code, possibly at the expense of 
  code size.

• opt_code_size pragma optcodesize- The compiler will optimize 
  code generation towards compact code, possibly at the expense 
  of code speed. 

• opt_code_balanced pragma optcodebalanced- The compiler will 
  attempt to generate code that is both compact and fast, as long 
  as meeting one goal is not a detriment to the other (this is 
  the default). 

• std_sdcc89 pragma stdsdcc89- Generally follow the C89 standard, 
  but allow SDCC features that conflict with the standard.

• std_c89 pragma stdc89- Follow the C89 standard and disable SDCC 
  features that conflict with the standard.

• std_sdcc99 pragma stdsdcc99- Generally follow the C99 standard, 
  but allow SDCC features that conflict with the standard.

• std_c99 pragma stdc99- Follow the C99 standard and disable SDCC 
  features that conflict with the standard.

• std_c11 pragma stdc11- Follow the C11 standard and disable SDCC 
  features that conflict with the standard.

• std_c2xpragma stdc2x- Follow the C2X standard and disable SDCC 
  features that conflict with the standard.

• codeseg <name>pragma codeseg- Use this name (max. 8 characters) 
  for the code segment. See option --codeseg.

• constseg <name>pragma constseg- Use this name (max. 8 
  characters) for the const segment. See option --constseg.

The preprocessorPreprocessor SDCPPsdcpp (preprocessor) supports 
the following #pragma directives:

• preproc_asmpragma preprocasm (+ | -) - switch the __asm 
  __endasm block preprocessing on / off. Default is on. Below is 
  an example on how to use this pragma.

#pragma preproc_asm -pragma preprocasm
/* this is a c code nop */
#define NOP ;

void foo (void)
{
   ...
   while (--i)
      NOP
   ...
   __asm
   ; this is an assembler nop instruction
   ; it is not preprocessed to ';' since the asm preprocessing is 
disabled
   NOP
   __endasm;
   ...
}


The pragma preproc_asm should not be used to define multilines of 
assembly code (even if it supports it), since this behavior is 
only a side effect of sdcpp __asm __endasm implementation in 
combination with pragma preproc_asm and is not in conformance 
with the C standard. This behavior might be changed in the future 
sdcpp versions. To define multilines of assembly code you have to 
include each assembly line into it's own __asm __endasm block. 
Below is an example for multiline assembly defines.

#define Nop __asm \
nop \
__endasm

#define ThreeNops Nop; \
Nop; \
Nop

void foo (void)
{
   ...
   ThreeNops;
   ...
}


• sdcc_hashpragma sdcchash (+ | -) - Allow "naked" hash in macro 
  definition, for example:
#define DIR_LO(x) #(x & 0xff)
Default is off. Below is an example on how to use this pragma.

#pragma preproc_asm +
#pragma sdcc_hash +pragma sdcchash

#define ROMCALL(x) \
   mov R6_B3, #(x & 0xff) \
   mov R7_B3, #((x >> 8) & 0xff) \
   lcall __romcall

...
__asm
ROMCALL(72)
__endasm;
...


Some of the pragmas are intended to be used to turn-on or off 
certain optimizations which might cause the compiler to generate 
extra stack and/or data space to store compiler generated 
temporary variables. This usually happens in large functions. 
Pragma directives should be used as shown in the following 
example, they are used to control options and optimizations for a 
given function. 

#pragma savepragma save        /* save the current settings */
#pragma nogcsepragma nogcse      /* turnoff global subexpression 
elimination */
#pragma noinductionpragma noinduction /* turn off induction 
optimizations */
int foo ()
{
    ...
    /* large code */
    ...
}
#pragma restorepragma restore /* turn the optimizations back on 
*/

The compiler will generate a warning message when extra space is 
allocated. It is strongly recommended that the save and restore 
pragmas be used when changing options for a function.

3.17 Defines Created by the Compiler

Besides defines from the C standards, the compiler creates the 
following #definesdefinesDefines created by the compiler:



+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| #define                                                                                                                  | Description                                                                                                                                                                                                                                                          |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCCSDCC!Defines!__SDCC (version macro)version macro                                                                   | Always defined. Version number string (e.g. SDCC_3_2_0 for sdcc 
3.2.0).                                                                                                                                                                                             |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| SDCC                                                                                                                     | OBSOLETE. WILL BE REMOVED IN THE FUTURE. CURRENTLY Only defined 
for the mcs51 backend (and only if –std-cXX is not used). This 
macro has been available since SDCC 2.5.6 and is the version 
number as an int (ex. 256). PLEASE USE OTHER VERSION MACROS 
INSTEAD! |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_mcs51SDCC!Defines!__SDCCmcs51 or __SDCC_ds390SDCC!Defines!__SDCCds390
 or __SDCC_z80SDCC!Defines!__SDCCz80, etc.  | depending on the model used (e.g.: -mds390). Older versions used 
SDCC_mcs51, etc instead.                                                                                                                                                                           |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_STACK_AUTOSDCC!Defines!SDCCSTACKAUTO                                                                              | when --stack-auto option is used                                                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_MODEL_SMALLSDCC!Defines!SDCCMODELSMALL                                                                            | when --model-small is used                                                                                                                                                                                                                                           |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_MODEL_MEDIUMSDCC!Defines!SDCCMODELMEDIUM                                                                          | when --model-medium is used                                                                                                                                                                                                                                          |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_MODEL_LARGESDCC!Defines!SDCCMODELLARGE                                                                            | when --model-large is used                                                                                                                                                                                                                                           |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_MODEL_HUGESDCC!Defines!SDCCMODELLARGE                                                                             | when --model-huge is used                                                                                                                                                                                                                                            |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_USE_XSTACKSDCC!Defines!SDCCUSEXSTACK                                                                              | when --xstack option is used                                                                                                                                                                                                                                         |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_STACK_TENBITSDCC!Defines!SDCCSTACKTENBIT (ds390)                                                                  | when -mds390 is used                                                                                                                                                                                                                                                 |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_MODEL_FLAT24SDCC!Defines!SDCCMODELFLAT24 (ds390)                                                                  | when -mds390 is used                                                                                                                                                                                                                                                 |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_VERSION_MAJOR                                                                                                     | Always defined. SDCC major version number. E.g. 3 for SDCC 3.5.0                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_VERSION_MINOR                                                                                                     | Always defined. SDCC minor version number. E.g. 5 for SDCC 3.5.0                                                                                                                                                                                                     |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_VERSION_PATCH                                                                                                     | Always defined. SDCC patchlevel version number. E.g. 0 for SDCC 
3.5.0                                                                                                                                                                                               |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_REVISIONSDCC!Defines!SDCCREVISION (svn revision number)                                                           | Always defined. SDCC svn revision number. Older versions of sdcc 
used SDCC_REVISION instead.                                                                                                                                                                        |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| SDCC_PARMS_IN_BANK1SDCC!Defines!SDCCPARMSINBANK1                                                                         | when --parms-in-bank1 is used                                                                                                                                                                                                                                        |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_ALL_CALLEE_SAVESSDCC!Defines!SDCCALLCALLEESAVES                                                                   | when --all-callee-saves is used                                                                                                                                                                                                                                      |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_FLOAT_REENTSDCC!Defines!SDCCFLOATREENT                                                                            | when --float-reent is used                                                                                                                                                                                                                                           |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_INT_LONG_REENTSDCC!Defines!SDCCINTLONGREENT                                                                       | when --int-long-reent is used                                                                                                                                                                                                                                        |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_OPTIMIZE_SPEEDSDCC!Defines!SDCCOPTIMIZESPEED                                                                      | when --opt-code-speed is used                                                                                                                                                                                                                                        |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCC_OPTIMIZE_SIZESDCC!Defines!SDCCOPTIMIZESIZE                                                                        | when --opt-code-size is used                                                                                                                                                                                                                                         |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+
| __SDCCCALLSDCC!Defines!SDCCCALL                                                                                          | Default ABI version for calling convention                                                                                                                                                                                                                           |
+--------------------------------------------------------------------------------------------------------------------------+----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------+


Notes on supported Processors

4.1 MCS51 variants<subsec:MCS51-variants>MCS51 variants

MCS51 processors are available from many vendors and come in many 
different flavours. While they might differ considerably in 
respect to Special Function Registers the core MCS51 is usually 
not modified or is kept compatible. 

4.1.1 pdata access by SFR

With the upcome of devices with internal xdata and flash memory 
devices using port P2P2 (mcs51 sfr) as dedicated I/O port is 
becoming more popular. Switching the high byte for __pdatapdata (mcs51, ds390 named address space)
 access which was formerly done by port P2 is then achieved by a 
Special Function Registersfr. In well-established MCS51 tradition 
the address of this sfr is where the chip designers decided to 
put it. Needless to say that they didn't agree on a common name 
either. So that the startup code can correctly initialize xdata 
variables, you should define an sfr with the name _XPAGEXPAGE (mcs51)
 at the appropriate location if the default, port P2, is not used 
for this. Some examples are:

__sfr __at (0x85) _XPAGE; /* Ramtron VRS51 family a.k.a. MPAGE */

__sfr __at (0x92) _XPAGE; /* Cypress EZ-USB family, Texas 
Instruments (Chipcon) a.k.a. MPAGE */

__sfr __at (0x91) _XPAGE; /* Infineon (Siemens) C500 family 
a.k.a. XPAGE */

__sfr __at (0xaf) _XPAGE; /* some Silicon Labs (Cygnal) chips 
a.k.a. EMI0CN */

__sfr __at (0xaa) _XPAGE; /* some Silicon Labs (Cygnal) chips 
a.k.a. EMI0CN */

There are also devices without anything resembling _XPAGE, but 
luckily they usually have dual data-pointers. For these devices a 
different method can be used to correctly initialize xdata 
variables. A default implementation is already in crtxinit.asm 
but it needs to be assembled manually with DUAL_DPTR set to 1.

For more exotic implementations further customizations may be 
needed. See section [subsec:MCS51-Startup-Code] for other 
possibilities.

4.1.2 Other Features available by SFR

Some MCS51 variants offer features like Dual DPTRDPTR, multiple 
DPTR, decrementing DPTR, 16x16 Multiply. These are currently not 
used for the MCS51 port. If you absolutely need them you can fall 
back to inline assembly or submit a patch to SDCC.

4.1.3 Bankswitching<subsec:Bankswitching>

BankswitchingBankswitching (a.k.a. code bankingcode banking) is a 
technique to increase the code space above the 64k limit of the 
8051.

4.1.3.1 Hardware


             +---------+--------+-------+
  8000-FFFF  | bank1   | bank2  | bank3 |
             +---------+--------+-------+
             +---------                  
  0000-7FFF  | common  |                 
             +---------                  
        SiLabs C8051F120 example         


Usually the hardware uses some sfr (an output port or an internal 
sfr) to select a bank and put it in the banked area of the memory 
map. The selected bank usually becomes active immediately upon 
assignment to this sfr and when running inside a bank it will 
switch out this code it is currently running. Therefor you cannot 
jump or call directly from one bank to another and need to use a 
so-called trampoline in the common area. For SDCC an example 
trampoline is in crtbank.asm and you may need to change it to 
your 8051 derivative or schematic. The presented code is written 
for the C8051F120.

When calling a banked function SDCC will put the LSB of the 
functions address in register R0, the MSB in R1 and the bank in 
R2 and then call this trampoline __sdcc_banked_call. The current 
selected bank is saved on the stack, the new bank is selected and 
an indirect jump is made. When the banked function returns it 
jumps to __sdcc_banked_ret which restores the previous bank and 
returns to the caller.

4.1.3.2 Software

When writing banked software using SDCC you need to use some 
special keywords and options. You also need to take over a bit of 
work from the linker.

To create a function that can be called from another bank it 
requires the keyword __bankedbanked. The caller must see this in 
the prototype of the callee and the callee needs it for a proper 
return. Called functions within the same bank as the caller do 
not need the __banked keyword nor do functions in the common 
area. Beware: SDCC does not know or check if functions are in the 
same bank. This is your responsibility!

Normally all functions you write end up in the segment CSEG. If 
you want a function explicitly to reside in the common area put 
it in segment HOME. This applies for instance to interrupt 
service routines as they should not be banked.

Functions that need to be in a switched bank must be put in a 
named segment. The name can be mostly anything up to eight 
characters (e.g. BANK1). To do this you either use --codeseg 
BANK1 (See [lyx:-codeseg]) on the command line when compiling or 
#pragma codeseg BANK1 (See [sec:Pragmas]) at the top of the C 
source file. The segment name always applies to the whole source 
file and generated object so functions for different banks need 
to be defined in different source files.

When linking your objects you need to tell the linker where to 
put your segments. To do this you use the following command line 
option to SDCC: -Wl-b BANK1=0x18000 (See [lyx:-Wl option]). This 
sets the virtual start address of this segment. It sets the 
banknumber to 0x01 and maps the bank to 0x8000 and up. The linker 
will not check for overflows, again this is your responsibility.

4.1.4 MCS51/DS390 Startup Code<subsec:MCS51-Startup-Code>

The compiler triggers the linker to link certain initialization 
modules from the runtime libraryRuntime library called 
crt<something>. Only the necessary ones are linked, for instance 
crtxstack.asm (GSINIT1, GSINIT5) is not linked unless the -
-xstack option is used. These modules are highly entangled by the 
use of special segments/areas, but a common layout is shown 
below:

(main.asm)

        .area HOME (CODE)
__interrupt_vect:
        ljmp __sdcc_gsinit_startup

(crtstart.asm)

        .area GSINIT0 (CODE)
__sdcc_gsinit_startup::
        mov sp,#__start__stack - 1

(crtxstack.asm)

        .area GSINIT1 (CODE)
__sdcc_init_xstack::
; Need to initialize in GSINIT1 in case the user's 
__sdcc_external_startup uses the xstack.
        mov __XPAGE,#(__start__xstack >> 8)
        mov _spx,#__start__xstack

(crtstart.asm)

        .area GSINIT2 (CODE)
        lcall ___sdcc_external_startup
        mov a,dpl
        jz __sdcc_init_data
        ljmp __sdcc_program_startup
__sdcc_init_data:

(crtxinit.asm)

        .area GSINIT3 (CODE)
__mcs51_genXINIT::
        mov r1,#l_XINIT
        mov a,r1
        orl a,#(l_XINIT >> 8)
        jz 00003$
        mov r2,#((l_XINIT+255) >> 8)
        mov dptr,#s_XINIT
        mov r0,#s_XISEG
        mov __XPAGE,#(s_XISEG >> 8)
00001$: clr a
        movc a,@a+dptr
        movx @r0,a
        inc dptr
        inc r0
        cjne r0,#0,00002$
        inc __XPAGE
00002$: djnz r1,00001$
        djnz r2,00001$
        mov __XPAGE,#0xFF
00003$:

(crtclear.asm)

        .area GSINIT4 (CODE)
__mcs51_genRAMCLEAR::
        clr a
        mov r0,#(l_IRAM-1)
00004$: mov @r0,a
        djnz r0,00004$
; _mcs51_genRAMCLEAR() end

(crtxclear.asm)

        .area GSINIT4 (CODE)
__mcs51_genXRAMCLEAR::
        mov r0,#l_PSEG
        mov a,r0
        orl a,#(l_PSEG >> 8)
        jz 00006$
        mov r1,#s_PSEG
        mov __XPAGE,#(s_PSEG >> 8)
        clr a
00005$: movx @r1,a
        inc r1
        djnz r0,00005$
00006$:
        mov r0,#l_XSEG
        mov a,r0
        orl a,#(l_XSEG >> 8)
        jz 00008$
        mov r1,#((l_XSEG + 255) >> 8)
        mov dptr,#s_XSEG
        clr a
00007$: movx @dptr,a
        inc dptr
        djnz r0,00007$
        djnz r1,00007$
00008$:

(crtxstack.asm)

        .area GSINIT5 (CODE)
; Need to initialize in GSINIT5 because __mcs51_genXINIT modifies 
__XPAGE
; and __mcs51_genRAMCLEAR modifies _spx.
        mov __XPAGE,#(__start__xstack >> 8)
        mov _spx,#__start__xstack

(application modules)

        .area GSINIT (CODE)

(main.asm)

        .area GSFINAL (CODE)
        ljmp __sdcc_program_startup
;--------------------------------------------------------
; Home
;--------------------------------------------------------
        .area HOME (CODE)
        .area CSEG (CODE)
__sdcc_program_startup:
        lcall _main
; return from main will lock up
        sjmp .

On some mcs51 variants __xdataxdata (mcs51, ds390 named address space
 memory has to be explicitly enabled before it can be accessed or 
if the watchdogwatchdog needs to be disabled, this is the place 
to do it. The startup code clears all internal data memory, 256 
bytes by default, but from 0 to n-1 if --iram-size--iram-size <Value>
 <n> is used. (recommended for Chipcon CC1010).

See also the compiler option --no-xinit-opt--no-xinit-opt and 
section [subsec:MCS51-variants] about MCS51-variants.


While these initialization modules are meant as generic startup 
code there might be the need for customization. Let's assume the 
return value of __sdcc_external_startup() in crtstart.asm should 
not be checked (or __sdcc_external_startup() should not be called 
at all). The recommended way would be to copy crtstart.asm (f.e. 
from 
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/device/lib/mcs51/crtstart.asm
) into the source directory, adapt it there, then assemble it 
with sdas8051 -plosgff[footnote:
”-plosgff” are the assembler options used in 
http://sdcc.svn.sourceforge.net/viewvc/sdcc/trunk/sdcc/device/lib/mcs51/Makefile.in?view=markup 
] crtstart.asm and when linking your project explicitly specify 
crtstart.rel. As a bonus a listing of the relocated object file 
crtstart.rst is generated.

4.1.5 Interfacing with Assembler CodeAssembler routines

4.1.5.1 Global Registers used for Parameter PassingParameter passing

The compiler always uses the global registers DPL, DPHDPTR, DPH, DPL
DPTR, BB (mcs51, ds390 register) and ACCACC (mcs51, ds390 register)
 to pass the first (non-bit) parameter to a function, and also to 
pass the return value return valueof function; according to the 
following scheme: one byte return value in DPL, two byte value in 
DPL (LSB) and DPH (MSB). three byte values (generic pointers) in 
DPH, DPL and B, and four byte values in DPH, DPL, B and ACC. 
Generic pointersgeneric pointer contain type of accessed memory 
in B: 0x00 – xdata/far, 0x40 – idata/near – , 0x60 – pdata, 0x80 
– code.

The second parameter onwards is either allocated on the stack 
(for reentrant routines or if --stack-auto is used) or in 
data/xdata memory (depending on the memory model).

Bit parameters are passed in a virtual register called 'bits' in 
bit-addressable space for reentrant functions or allocated 
directly in bit memory otherwise.

Functions (with two or more parameters or bit parameters) that 
are called through function pointersfunction pointers must 
therefor be reentrant so the compiler knows how to pass the 
parameters.

4.1.5.2 Register usage

Unless the called function is declared as _nakednaked, or the -
-callee-saves--callee-saves/--all-callee-saves command line 
option or the corresponding callee_saves pragma are used, the 
caller will save the registers (R0-R7) around the call, so the 
called function can destroy they content freely.

If the called function is not declared as _naked, the caller will 
swap register banks around the call, if caller and callee use 
different register banks (having them defined by the __using 
modifier). 

The called function can also use DPL, DPH, B and ACC observing 
that they are used for parameter/return value passing.

4.1.5.3 Assembler Routine (non-reentrant)

In the following examplereentrantAssembler routines (non-reentrant)
 the function c_func calls an assembler routine asm_func, which 
takes two parametersfunction parameter.

extern int asm_func(unsigned char, unsigned char);

int c_func (unsigned char i, unsigned char j)
{
    return asm_func(i,j);
}

int main()
{
    return c_func(10,9);
}

The corresponding assembler function is:

        .globl _asm_func_PARM_2
        .globl _asm_func
        .area OSEG
_asm_func_PARM_2:
        .ds    1
        .area CSEG
_asm_func:
        mov    a,dpl
        add    a,_asm_func_PARM_2
        mov    dpl,a
        mov    dphDPTR, DPH, DPL,#0x00
        ret

The parameter naming convention is _<function_name>_PARM_<n>, 
where n is the parameter number starting from 1, and counting 
from the left. The first parameter is passed in DPH, DPL, B and 
ACC according to the description above. The variable name for the 
second parameter will be _<function_name>_PARM_2.

Assemble the assembler routine with the following command:

sdas8051 -losg asmfunc.asm

Then compile and link the assembler routine to the C source file 
with the following command:

sdcc cfunc.c asmfunc.rel

4.1.5.4 Assembler Routine (reentrant)

In this casereentrantAssembler routines (reentrant) the second 
parameterfunction parameter onwards will be passed on the stack, 
the parameters are pushed from right to left i.e. before the call 
the second leftmost parameter will be on the top of the stack 
(the leftmost parameter is passed in registers). Here is an 
example:

extern int asm_func(unsigned char, unsigned char, unsigned char) 
reentrant;

int c_func (unsigned char i, unsigned char j, unsigned char k) 
reentrant 
{
    return asm_func(i,j,k);
}

int main()
{
    return c_func(10,9,8);
}

The corresponding (unoptimized) assembler routine is:

.globl _asm_func
_asm_func:
    push _bp
    mov  _bp,sp      ;stack contains: _bp, return address, second 
parameter, third parameter
    mov  r2,dpl
    mov  a,_bp
    add  a,#0xfd     ;calculate pointer to the second parameter
    mov  r0,a
    mov  a,_bp
    add  a,#0xfc     ;calculate pointer to the rightmost 
parameter
    mov  r1,a
    mov  a,@r0
    add  a,@r1
    add  a,r2        ;calculate the result (= sum of all three 
parameters)
    mov  dpl,a       ;return value goes into dptr (cast into int)
    mov  dph,#0x00
    mov  sp,_bp
    pop  _bp
    ret

The compiling and linking procedure remains the same, however 
note the extra entry & exit linkage required for the assembler 
code, _bp is the stack frame pointer and is used to compute the 
offset into the stack for parameters and local variables.

4.2 DS400 port

The DS80C400DS80C400DS400 microcontroller has a rich set of 
peripherals. In its built-in ROM library it includes functions to 
access some of the features, among them is a TCP stack with IP4 
and IP6 support. Library headers (currently in beta status) and 
other files are provided at 
ftp://ftp.dalsemi.com/pub/tini/ds80c400/c_libraries/sdcc/index.html
. 

4.3 The Z80, Z180, Rabbit 2000, Rabbit 2000A, Rabbit 3000A, SM83 
  (GameBoy), eZ80 and TLCS-90 ports

SDCC can target the Z80Z80, Z180, eZ80 in Z80 mode, Rabbit 2000, 
Rabbit 2000A, Rabbit 3000A and LR35902, the Sharp SM83 (used .e.g 
in the Nintendo GameBoy) sm83sm83 (GameBoy Z80).

When a frame pointer is used, it resides in IX. Register A, B, C, 
D, E, H, L and IY are used as a temporary registers for holding 
variables.

When enabling optimizations using --opt-code size and a 
sufficiently high value for --max-allocs-per-node SDCC typically 
generates much better code for these architectures than many 
other compilers. A comparison of compilers for these architecture 
can be found at http://sdcc.sourceforge.net/wiki/index.php/Z80_code_size
.

4.3.1 Startup Code

On the Z80Z80 the startup code is inserted by linking with 
crt0.rel which is generated from sdcc/device/lib/z80/crt0.s. If 
you need a different startup code you can use the compiler option 
--no-std-crt0--no-std-crt0 and provide your own crt0.rel. When 
using a custom crt0.rel it needs to be listed first when linking.

4.3.2 Rabbit ports

SDCC has three Rabbit-supporting ports: r2k for the Rabbit 2000, 
r2ka for the Rabbit 2000A, 2000B, 2000C and 3000, r3ka for the 
Rabbit 3000A. The instruction set of the Rabbit 2000 to Rabbit 
3000 is the same, and a subset of the Rabbit 3000A instruction 
set. Code from the r2k backend will work on Rabbit 2000 to 3000A 
and code from the r2ka backend will work on Rabbit 2000A to 
3000A. In some hardware configurations (see below), code from the 
r2ka backend will work on the Rabbit 2000. Typically, code from 
the r3ka backend will be faster and smaller than code from the 
r2ka backend, and code from the r2ka backend will be faster and 
smaller than code from the r2k backend.

4.3.2.1 Rabbit wait states

There are multiple wait state bugs present in some of the the 
Rabbits. The difference between the r2k and r2ka port is in 
additional wait state bug workarounds. If all memory used has 
zero wait states, code from the r2ka backend can be safely run on 
the original Rabbit 2000.

Note that The r2k and r2ka port assume that the whole stack has 
the same number of wait states (code from the r2k and r2ka ports 
can fail is the stack spans memories with a different amount of 
wait states).

The Rabbit 2000 has some wait state bugs that SDCC does not work 
around. These bugs result in the number of wait states used being 
one less than configured for some instructions. The workaround 
has to be supplied by the user, by configuring all memories that 
do use wait states to use on additional wait state.

For all Rabbit ports, SDCC assumes that all data memory is at 
least as fast (i.e. does not need more wait states) as all code 
memory. Code where this is not the case (e.g. code in fast Flash 
writing into slow battery-backed SRAM) will have to be written in 
assembler by hand.

4.3.3 Z80, Z180 and Z80N calling conventions

The current default is the SDCC calling convention, version 1. 
Using the command-line option –sdcccall 0, the default can be 
changed to version 0. There are three other calling conventions 
supported, which can be specified using the keywords __smallc, 
__z88dk_fastcall and __z88dk_callee. They are primarily intended 
for compatibility with libraries written for other compilers. For 
__z88dk_fastcall, there may be only one parameter of at most 32 
bits, which is passed the same way as the return value of 
__sdcccall(0). For __z88dk_callee, the stack is not adjusted for 
stack parameters the parameters after the call (thus the callee 
has to do this instead). __z88dk_callee can be combined with 
__smallc, __sdcccall(0) or __sdcccall(1).

4.3.3.1 Z80 SDCC calling convention, version 1

This calling convention can be chosen per function via 
__sdcccall(1). 8-bit return values are passed in a, 16-bit values 
in de, 24-bit values in lde, 32-bit values in hlde. Larger return 
values (as well as struct and union independent of their size) 
are passed in memory in a location specified by the caller 
through a hidden pointer argument.

For functions that have variable arguments: All parameters are 
passed on the stack. The stack is not adjusted for the parameters 
by the callee (thus the caller has to do this instead).

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/z80-arguments.svg>

For Functions that do not have variable arguments: the first 
parameter is passed in a if it has 8 bits. If it has 16 bits it 
is passed in hl. If it has 32 bits, it is passed in hlde. If the 
first parameter is in a, and the second has 8 bits, it is passed 
in l; if the first is passed in a or hl, and the second has 16 
bits, it is passed in de; all other parameters are passed on the 
stack, right-to-left. Independent of their size, struct / union 
parameters and all following parameters are always passed on the 
stack.

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/z80-stack-cleanup.svg>

If __z88dk_callee is not used, after the call, the stack 
parameters are cleaned up by the caller, with the following 
exceptions: functions that do not have variable arguments and 
return void or a type of at most 16 bits, or have both a first 
parameter of type float and a return value of type float.

4.3.3.2 Z80 SDCC calling convention, version 0

This calling convention can be chosen per function via 
__sdcccall(0). All parameters are passed on the stack, 
right-to-left. 8-bit return values are passed in l, 16-bit values 
in hl, 24-bit values in ehl, 32-bit values in dehl. Except for 
the SM83, where 8-bit values are passed in e, 16-bit values in 
de, 32-bit values in hlde. Larger return values (as well as 
struct and union independent of their size) are passed in a 
memory in a location specified by the caller through a hidden 
pointer argument. Unless __z88dk_callee is used, all stack 
parameters are cleaned up by the caller.

4.3.4 Rabbit 2000, Rabbit 2000A, Rabbit 3000A, eZ80 and TLCS-90 
  calling conventions

The default is the Z80 SDCC calling convention, version 0 as 
described above. Using the command-line option –sdcccall 1, the 
default can be changed to version 1 of the Rabbit SDCC calling 
convention. There are four other calling conventions supported, 
which can be specified using the keywords __smallc, 
__z88dk_fastcall and __z88dk_callee. They are primarily intended 
for compatibility with libraries written for other compilers. For 
__z88dk_fastcall, there may be only one parameter of at most 32 
bits, which is passed the same way as the return value. For 
__z88dk_callee, the stack is not adjusted for stack parameters 
the parameters after the call (thus the callee has to do this 
instead). __z88dk_callee can be combined with __smallc, 
__sdcccall(0) or __sdcccall(1).

4.3.4.1 Rabbit SDCC calling convention, version 1

This calling convention can be chosen per function via 
__sdcccall(1). 8-bit return values are passed in a, 16-bit values 
in hl, 24-bit values in lde, 32-bit values in hlde. Larger return 
values (as well as struct and union independent of their size) 
are passed in memory in a location specified by the caller 
through a hidden pointer argument.

For functions that have variable arguments: All parameters are 
passed on the stack. The stack is not adjusted for the parameters 
by the callee (thus the caller has to do this instead).

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/r3ka-arguments.svg>

For Functions that do not have variable arguments: the first 
parameter is passed in a if it has 8 bits. If it has 16 bits it 
is passed in hl. If it has 32 bits, it is passed in hlde. If the 
first parameter is in a, and the second has 8 bits, it is passed 
in l; if the first is in hl or hlde, and the second has 8 bits, 
it is passed in a; if the first is in a, and the second has 16 
bits, it is passed in hl; all other parameters are passed on the 
stack, right-to-left. Independent of their size, struct / union 
parameters and all following parameters are always passed on the 
stack.

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/z80-stack-cleanup.svg>

If __z88dk_callee is not used, after the call, the stack 
parameters are cleaned up by the caller, with the following 
exceptions: functions that do not have variable arguments and 
return void or a type of at most 16 bits, or have both a first 
parameter of type float and a return value of type float.

4.3.5 SM83 calling conventions

The current default is the SDCC calling convention, version 1. 
Using the command-line option –sdcccall 0, the default can be 
changed to version 0.

4.3.5.1 SM83 SDCC calling convention, version 1

This calling convention can be chosen per function via 
__sdcccall(1).

8-bit return values are passed in a, 16-bit values in bc, 32-bit 
values in debc. Larger return values (as well as struct and union 
independent of their size) are passed in memory in a location 
specified by the caller through a hidden pointer argument.

For functions that have variable arguments: All parameters are 
passed on the stack. The stack is not adjusted for the parameters 
by the callee (thus the caller has to do this instead).

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/sm83-arguments.svg>

For Functions that do not have variable arguments: the first 
parameter is passed in a if it has 8 bits. If it has 16 bits it 
is passed in de. If it has 32 bits, it is passed in debc. If the 
first parameter is in a, and the second has 8 bits, it is passed 
in e; if the first is in bc or debc, and the second has 8 bits, 
it is passed in a; if the first is passed in a, and the second 
has 16 bits, it is passed in bc; if the first is passed in de, 
and the second has 16 bits, it is passed in bc; all other 
parameters are passed on the stack, right-to-left. Independent of 
their size, struct / union parameters and all following 
parameters are always passed on the stack. The stack is adjusted 
by the callee (thus explicitly specifying __z88dk_callee does not 
make a difference), unless the functionhas variable arguments.

4.3.5.2 SM83 SDCC calling convention, version 0

This calling convention can be chosen per function via 
__sdcccall(0). 8-bit return values are passed in e, 16-bit values 
in de, 32-bit values in hlde. Larger return values (as well as 
struct and union independent of their size) are passed in memory 
in a location specified by the caller through a hidden pointer 
argument. All parameters are passed on the stack. The stack is 
not adjusted for the parameters by the callee (thus the caller 
has to do this instead), unless __z88dk_callee is specified. 
__sdcccall(0) can be combined with __z88dk_callee.

4.3.6 Small-C calling convention

Functions declared as __smallc are called using the Small-C 
calling convention (passing arguments on-stack left-to-right, 1 
byte arguments are passed as 2 bytes, with the value in the lower 
byte). 8-bit return values are passed in a, 16-bit values in de, 
32-bit values in hlde. Larger return values (as well as struct 
and union independent of their size) are passed in memory in a 
location specified by the caller through a hidden pointer 
argument. This way assembler routines originally written for 
Small-C or code generated by Small-C can be called from SDCC. 
Currently variable arguments are not yet supported (neither on 
the caller nor on the callee side).

4.3.7 Complex instructions

The Z80 and some derivatives support complex instructions, such 
as ldir, cpir, ... . SDCC only emits these instructions for 
functions in the standard library. Thus, e.g. copying one array 
into another is more efficient when using memcpy() than by using 
a a user-written loop.

Depending on the target, code generation options and the 
parameters to the call, SDCC emits ldir for memcpy(), ldir or 
lsidr for memset(), ldi for strcpy(), ldi for strncpy(). Other 
library functions use the complex instructions as well, but for 
those, function calls are generated.

4.3.8 Unsafe reads

Usually, Z80-based systems (except for the SM83 and TLCS-90) have 
separate I/O and memory spaces, and any normal memory location 
can be read without side-effects. For such systems, the option 
–allow-unsafe-reads can be used to enable some extra 
optimizations that rely on this.

4.3.9 Z80 banked calls

Banked calls are supported via __banked. Banked calls are done 
via a trampoline (__sdcc_bcall if --legacy-banking is specified, 
__sdcc_bcall_abc for z88dk_fastcall, __sdcc_bcall_ehl for other 
calls). Default trampolines are provided in the library. The 
default trampolines calls user supplied helper functions set_bank 
and get_bank that set the current bank to the value in register 
a, or return the current bank in register a.

For banked functions, the calling convention is slightly 
different: the stack is always cleared up by the caller. Unless 
__z88dk_fastcall is used, all parameters are passed on the stack.

4.4 The HC08 and S08 ports

The port to the Freescale/Motorola HC08HC08 and S08 does not yet 
generate code as compact as that generated by some non-free 
compilers. A comparison of compilers for these architecture can 
be found at http://sdcc.sourceforge.net/wiki/index.php/Hc08_code_size
.

4.4.1 Startup Code

The HC08HC08 startup code follows the same scheme as the MCS51 
startup code.

4.5 The STM8 port

4.5.1 Calling conventions

By default, the SDCC calling convention, version 1 is used. Using 
the option –sdcccall 0, the default can be changed to version 0.

Arguments are passed on the stack right-to-left. Return values 
are in a (8 bit), x (16 bit), xyl (24 bit), xy (32 bit) or use a 
hidden extra pointer parameter pointing to the location (anything 
wider than 32 bit, and all struct / union).

4.5.1.1 SDCC calling convention, version 1

<Graphics file: /home/sdcc-builder/build/sdcc-build/amd64-unknown-linux2.5.build/sdcc/doc/stm8-arguments.svg>

For functions that have variable arguments, all parameters are 
passed on the stack. For other functions, if the first parameter 
has 8 or 16 bits, it is passed in a or x. If the first parameter 
is passed in a, and the second has 16 bits, the second is passed 
in x. If the first parameter is passed in x, and the second has 8 
bits, the second is passed in a. All other parameters are passed 
on the stack. Independent of their size, struct / union 
parameters and all following parameters are always passed on the 
stack. If __z88dk_callee is specified, the stack is always 
adjusted by the callee. Otherwise, for the large memory model, 
the stack is always adjusted by the caller. For the medium memory 
model the stack is adjusted by the caller, with the following 
exceptions: functions that do not have variable arguments and 
return void or a type of at most 16 bits, or have both a first 
parameter of type float and a return value of type float.

4.5.1.2 SDCC calling convention, version 0

This calling convention can be chosen per function via 
__sdcccall(0) (e.g. for compatibility with functions written in 
assembler for use with older versions of SDCC). All parameters 
are passed on the stack. The stack is not adjusted for the 
parametersby the callee (thus the caller has to do this instead), 
unless __z88dk_callee is specified.

4.5.1.3 Raisonance calling convention

For compatibility with the Raisonance STM8 compiler, the 
__raisonance calling convention is supported. If the first 
parameter is 8 or 16 bits, it is passed in a or x. If the first 
parameter is 8 bits, and the second 16 bits, the second is passed 
in x. If the first parameter is 16 bits, and the second is 8 
bits, the second is passed in a. All other parameters are passed 
on the stack. If the return value is 8 bits, it is passed in a. 
If it is 16 bits, it is passed in x. Raisonance passes larger 
return values in pseudoregisters, which is not supported by SDCC.

4.5.1.4 IAR calling convention

For compatibility with the IAR STM8 compiler, the __iar calling 
convention is supported. The first 8-bit parameter is passed in 
a, the first 16-bit parameter in x, the second 16-bit parameter 
in y. Further parameters of up to 32 bits are passed in 
pseudoregisters, which is not supported by SDCC. All other 
parameters are passed on the stack. If the return value is 8 
bits, it is passed in a. If it is 16 bits, it is passed in x. IAR 
passes larger return values in pseudoregisters, which is not 
supported by SDCC.

4.5.1.5 Cosmic calling convention

For compatibility with the Cosmic STM8 compiler, the __cosmic 
calling convention is supported. If the first parameter is 8 or 
16 bits, it is passed in a or x. If the return value is 8 bits, 
it is passed in a. If it is 16 bits, it is passed in x. Cosmic 
passes larger return values in pseudoregisters, which is not 
supported by SDCC. Even for the medium memory model, __cosmic 
functions use a 24-bit return address in their stack frame, and 
are called using callf.

4.6 The PIC14PIC14 port

The PIC14 port adds support for MicrochipMicrochip^{\text{TM}} 
PICPIC14^{\text{TM}} MCUs with 14 bit wide instructions. This 
port is not yet mature and still lacks many features. However, it 
can work for simple code.

Currently supported devices include:





10F320, 10F322, 10LF320, 10LF322

12F609, 12F615, 12F617, 12F629, 12F635, 12F675, 12F683

12F752

12HV752

16C62, 16C63A, 16C65B

16C71, 16C72, 16C73B, 16C74B

16C432, 16C433

16C554, 16C557, 16C558

16C620, 16C620A, 16C621, 16C621A, 16C622, 16C622A

16C710, 16C711, 16C715, 16C717, 16C745, 16C765, 16C770, 16C771, 
16C773, 16C774, 16C781, 16C782

16C925, 16C926 

16CR73, 16CR74, 16CR76, 16CR77

16CR620A

16F72 ,16F73, 16F74, 16F76, 16F77

16F84, 16F84A, 16F87, 16F88

16F610, 16F616, 16F627, 16F627A, 16F628, 16F628A, 16F630, 16F631, 
16F636, 16F639, 16F648A

16F676, 16F677, 16F684, 16F685, 16F687, 16F688, 16F689, 16F690

16F707, 16F716, 16F720, 16F721, 16F722, 16F722A, 16F723, 16F723A, 
16F724, 16F726, 16F727

16F737, 16F747, 16F753, 16F767, 16F777, 16F785

16F818, 16F819, 16F870, 16F871, 16F872, 16F873, 16F873A, 16F874, 
16F874A, 16F876, 16F876A

16F877, 16F877A, 16F882, 16F883, 16F884, 16F886, 16F887

16F913, 16F914, 16F916, 16F917, 16F946

16LF74, 16LF76, 16LF77

16LF84, 16LF84A, 16LF87, 16LF88

16LF627, 16LF627A, 16LF628, 16LF628A, 16LF648A

16LF707, 16LF720, 16LF721, 16LF722, 16LF722A, 16LF723, 16LF723A, 
16LF724, 16LF726, 16LF727 

16LF747, 16LF767, 16LF777

16LF818, 16LF819, 16LF870, 16LF871, 16LF872, 16LF873, 16LF873A, 
16LF874, 16LF874A

16LF876, 16LF876A, 16LF877, 16LF877A

16HV610, 16HV616, 16HV753, 16HV785





Supported devices with enhanced cores:





12F1501, 12F1571, 12F1572, 12F1612, 12F1822, 12F1840

12LF1501, 12LF1552, 12LF1571, 12LF1572, 12LF1612, 12LF1822, 
12LF1840, 12LF1840T39A, 12LF1840T48A

16F1454, 16F1455, 16F1458, 16F1459

16F1503, 16F1507, 16F1508, 16F1509, 16F1512, 16F1513, 16F1516, 
16F1517, 16F1518, 16F1519

16F1526, 16F1527, 16F1574, 16F1575, 16F1578, 16F1579

16F1613, 16F1614, 16F1615, 16F1618, 16F1619

16F1703, 16F1704, 16F1705, 16F1707, 16F1708, 16F1709, 16F1713, 
16F1716, 16F1717, 16F1718, 16F1719

16F1764, 16F1765, 16F1768, 16F1769, 16F1773, 16F1776, 16F1777, 
16F1778, 16F1779

16F1782, 16F1783, 16F1784, 16F1786, 16F1787, 16F1788, 16F1789

16F1823, 16F1824, 16F1825, 16F1826, 16F1827, 16F1828, 16F1829, 
16F1829LIN, 16F1847

16F1933, 16F1934, 16F1936, 16F1937, 16F1938, 16F1939, 16F1946, 
16F1947

16F18313, 16F18323, 16F18324, 16F18325, 16F18344, 16F18345,

16F18855, 16F18875

16LF1454, 16LF1455, 16LF1458, 16LF1459

16LF1503, 16LF1507, 16LF1508, 16LF1509, 16LF1512, 16LF1513, 
16LF1516, 16LF1517, 16LF1518, 16LF1519,

16LF1526, 16LF1527 

16LF1554, 16LF1559, 16LF1566, 16LF1567, 16LF1574, 16LF1575, 
16LF1578, 16LF1579

16LF1613, 16LF1614, 16LF1615, 16LF1618, 16LF1619

16LF1703, 16LF1704, 16LF1705, 16LF1707, 16LF1708, 16LF1709, 
16LF1713, 16LF1716, 16LF1717, 16LF1718, 16LF1719 

16LF1764, 16LF1765, 16LF1768, 16LF1769, 16LF1773, 16LF1776, 
16LF1777, 16LF1778, 16LF1779

16LF1782, 16LF1783, 16LF1784, 16LF1786, 16LF1787, 16LF1788, 
16LF1789,

16LF1823, 16LF1824, 16LF1824T39A

16LF1825, 16LF1826, 16LF1827, 16LF1828, 16LF1829, 16LF1847

16LF1902, 16LF1903, 16LF1904, 16LF1906, 16LF1907

16LF1933, 16LF1934, 16LF1936, 16LF1937, 16LF1938, 16LF1939, 
16LF1946, 16LF1947

16LF18313, 16LF18323, 16LF18324, 16LF18325, 16LF18344, 16LF18345

16LF18855, 16LF18875





An up-to-date list of currently supported devices can be obtained 
via sdcc -mpic14 -phelp foo.c (foo.c must exist...).

4.6.1 PIC Code Pagescode page (pic14) and Memory BanksMemory bank (pic14)

The linker organizes allocation for the code page and RAM banks. 
It does not have intimate knowledge of the code flow. It will put 
all the code section of a single .asm file into a single code 
page. In order to make use of multiple code pages, separate asm 
files must be used. The compiler assigns all static functions of 
a single .c file into the same code page.

To get the best results, follow these guidelines:

1. Make local functions static, as non static functions require 
  code page selection overhead.
Due to the way SDCC handles functions, place called functions 
  prior to calling functions in the file wherever possible: 
  Otherwise SDCC will insert unnecessary pagesel directives 
  around the call, believing that the called function is 
  externally defined.

2. For devices that have multiple code pages it is more efficient 
  to use the same number of files as pages: Use up to 4 separate 
  .c files for the 16F877, but only 2 files for the 16F874. This 
  way the linker can put the code for each file into different 
  code pages and there will be less page selection overhead.

3. And as for any 8 bit micro (especially for PIC14 as they have 
  a very simple instruction set), use `unsigned char' wherever 
  possible instead of `int'.

4.6.2 Adding New Devices to the Port 

Adding support for a new 14bit PIC MCU requires the following 
steps:

1. Create a new device description.
Each device is described in two files: pic16f*.h and pic16f*.c. 
  These files primarily define SFRs, structs to access their 
  bits, and symbolic configuration options. Both files can be 
  generated from gputils' .inc files using the perl script 
  support/scripts/inc2h.pl. This file also contains further 
  instructions on how to proceed.

2. Copy the .h file into SDCC's include path and either add the 
  .c file to your project or copy it to device/lib/pic/libdev. 
  Afterwards, rebuild and install the libraries.

3. Edit pic14devices.txt in SDCC's include path 
  (device/include/pic/ in the source tree or 
  /usr/local/share/sdcc/include/pic after installation).
You need to add a device specification here to make the memory 
  layout (code banks, RAM, aliased memory regions, ...) known to 
  the compiler. Probably you can copy and modify an existing 
  entry. The file format is documented at the top of the file.

4.6.3 Interrupt Code

For the interrupt function, use the keyword __interruptPIC14!interrupt
 with level number of 0 (PIC14 only has 1 interrupt so this 
number is only there to avoid a syntax error - it ought to be 
fixed). E.g.:

void Intr(void) __interrupt (0)
{
  T0IF = 0; /* Clear timer interrupt */
}

4.6.4 Configuration Bits

Configuration bits (also known as fuses) can be configured using 
`__code' and `__at' modifiers. Possible options should be ANDed 
and can be found in your processor header file. Example for 
PIC16F88:

#include <pic16f88.h> //Contains config addresses and options
#include <stdint.h> //Needed for uint16_t

static __code uint16_t __at (_CONFIG1) configword1 = _INTRC_IO &
  _CP_ALL & _WDT_OFF & [...];
static __code uint16_t __at (_CONFIG2) configword2 = [...];

Although data type is ignored if the address (__at()) refers to a 
config word location, using a type large enough for the 
configuration word (uint16_t in this case) is recommended to 
prevent changes in the compiler (implicit, early range check and 
enforcement) from breaking the definition.

If your processor header file doesn't contain config addresses 
you can declare it manually or use a literal address:

static __code uint16_t __at (0x2007) configword1 = _INTRC_IO &
  _CP_ALL & _WDT_OFF & [...];

4.6.5 Linking and Assembling

For assembling you can use either GPUTILS'gputils (pic tools) 
gpasm.exe or MPLAB's mpasmwin.exe. GPUTILS are available from http://sourceforge.net/projects/gputils
. For linking you can use either GPUTILS' gplink or MPLAB's 
mplink.exe. If you use MPLAB and an interrupt function then the 
linker script file vectors section will need to be enlarged to 
link with mplink.

Pic device specific header and c source files are automatically 
generated from MPLAB include files, which are published by 
Microchip with a special requirement that they are only to be 
used with authentic Microchip devices. This reqirement prevents 
to publish generated header and c source files under the GPL 
compatible license, so they are located in non-free directory 
(see section [subsec:Search-Paths]). In order to include them in 
include and library search paths, the --use-non-free--use-non-free
 command line option should be defined.

NOTE: the compiled code, which use non-free pic device specific 
libraries, is not GPL compatible!

Here is a Makefile using GPUTILS:

.c.o:
        sdcc -V --use-non-free -mpic14 -p16f877 -c $<

$(PRJ).hex: $(OBJS)
        gplink -m -s $(PRJ).lkr -o $(PRJ).hex $(OBJS) libsdcc.lib

Here is a Makefile using MPLAB:

.c.o: 
        sdcc -S -V --use-non-free -mpic14 -p16f877 $<
        mpasmwin /q /o $*.asm

$(PRJ).hex: $(OBJS)
        mplink /v $(PRJ).lkr /m $(PRJ).map /o $(PRJ).hex $(OBJS) 
libsdcc.lib

Please note that indentations within a Makefile have to be done 
with a tabulator character.

4.6.6 Command-Line Options

Besides the switches common to all SDCC backends, the PIC14 port 
accepts the following options (for an updated list see sdcc -
-help):

  --debug-xtraPIC14!Options!--debug-extra emit debug info in 
  assembly output

  --no-pcode-optPIC14!Options!--no-pcode-opt disable (slightly 
  faulty) optimization on pCode

  --stack-locPIC14!Options!--stack-loc sets the lowest address of 
  the argument passing stack (defaults to a suitably large shared 
  databank to reduce BANKSEL overhead)

  --stack-sizePIC14!Options!--stack-size sets the size if the 
  argument passing stack (default: 16, minimum: 4)

  --use-non-freePIC14!Options!--use-non-free make non-free device 
  headers and libraries available in the compiler's search paths 
  (implicit -I and -L options)

  --no-extended-instructions forbid use of the extended 
  instruction set (e.g., ADDFSR)

4.6.7 Environment Variables

The PIC14 port recognizes the following environment variables:

  SDCC_PIC14_SPLIT_LOCALSPIC14!Environment variables!SDCCPIC14SPLITLOCALS
  SDCC!Environment variables!SDCCPIC14SPLITLOCALS If set and not 
  empty, sdcc will allocate each temporary register (the ones 
  called r0xNNNN) in a section of its own. By default (if this 
  variable is unset), sdcc tries to cluster registers in sections 
  in order to reduce the BANKSEL overhead when accessing them.

4.6.8 The Library

The PIC14 library currently only contains support routines 
required by the compiler to implement multiplication, division, 
and floating point support. No libc-like replacement is available 
at the moment, though many of the common sdcc library sources (in 
device/lib) should also compile with the PIC14 port.

4.6.8.1 Enhanced cores

SDCC/PIC14 has experimental support for devices with the enhanced 
14-bit cores (such as pic12f1822). Due to differences in required 
code, the libraries provided with SDCC (libm.lib and libsdcc.lib) 
are now provided in two variants: libm.lib and libsdcc.lib are 
compiled for the regular, non-enhanced devices. libme.lib and 
libsdcce.lib (note the trailing 'e') are compiled for enhanced 
devices. When linking manually, make sure to select the proper 
variant!

When SDCC is used to invoke the linker, SDCC will automatically 
select the libsdcc.lib-variant suitable for the target device. 
However, no such magic has been conjured up for libm.lib!

4.6.8.2 Accessing bits of special function registers

Individual bits within SFRs can be accessed either using 
<sfrname>bits.<bitname> or using a shorthand <bitname>, which is 
defined in the respective device header for all <bitname>s. In 
order to avoid polluting the global namespace with the names of 
all the bits, you can #define NO_BIT_DEFINES before inclusion of 
the device header file.

4.6.8.3 Naming of special function registers<subsec:Naming-of-special>

If NO_BIT_DEFINES is used, individual bits of the SFRs can be 
accessed as <sfrname>bits.<bitname>. With the 3.1.0 release, the 
previously used <sfrname>_bits.<bitname> (note the underscore) is 
deprecated. This was done to align the naming conventions with 
the PIC16 port and competing compiler vendors. To avoid polluting 
the global namespace with the legacy names, you can prevent their 
definition using #define NO_LEGACY_NAMES prior to the inclusion 
of the device header.

You must also #define NO_BIT_DEFINES in order to access SFRs as 
<sfrname>bits.<bitname>, otherwise <bitname> will expand to 
<sfrname>bits.<bitname>, yielding the undefined expression 
<sfrname>bits.<sfrname>bits.<bitname>.

4.6.8.4 error: missing definition for symbol ``__gptrget1''

The PIC14 port uses library routines to provide more complex 
operations like multiplication, division/modulus and (generic) 
pointer dereferencing. In order to add these routines to your 
project, you must link with PIC14's libsdcc.lib. For single 
source file projects this is done automatically, more complex 
projects must add libsdcc.lib to the linker's arguments. Make 
sure you also add an include path for the library (using the -I 
switch to the linker)!

4.6.8.5 Processor mismatch in file ``XXX''.

This warning can usually be ignored due to the very good 
compatibility amongst 14bit PICPIC14 devices.

You might also consider recompiling the library for your specific 
device by changing the ARCH=p16f877 (default target) entry in 
device/lib/pic/Makefile.in and device/lib/pic/Makefile to reflect 
your device. This might even improve performance for smaller 
devices as unnecessary BANKSELs might be removed.

4.6.9 Known Bugs

4.6.9.1 Function arguments

Functions with variable argument lists (like printf) are not yet 
supported. Similarly, taking the address of the first argument 
passed into a function does not work: It is currently passed in 
WREG and has no address...

4.6.9.2 Regression tests fail

Though the small subset of regression tests in src/regression 
passes, SDCC regression test suite does not, indicating that 
there are still major bugs in the port. However, many smaller 
projects have successfully used SDCC in the past...

4.7 The PIC16PIC16 port

The PIC16 port adds support for MicrochipMicrochip^{\text{TM}} 
PICPIC^{\text{TM}} MCUs with 16 bit wide instructions. This port 
is not yet mature and still lacks many features. However, it can 
work for simple code. Currently this family of microcontrollers 
contains the PIC18Fxxx and PIC18Fxxxx; devices supported by the 
port include:





18F13K22 18F13K50

18F14K22 18F14K50

18F23K20 18F23K22

18F24J10 18F24J11 18F24J50 18F24K20 18F24K22 18F24K50

18F25J10 18F25J11 18F25J50 18F25K20 18F25K22 18F25K50 18F25K80

18F26J11 18F26J13 18F26J50 18F26J53 18F26K20 18F26K22 18F26K80

18F27J13 18F27J53

18F43K20 18F43K22

18F44J10 18F44J11 18F44J50 18F44K20 18F44K22

18F45J10 18F45J11 18F45J50 18F45K20 18F45K22 18F45K50 18F45K80

18F46J11 18F46J13 18F46J50 18F46J53 18F46K20 18F46K22 18F46K80

18F47J13 18F47J53

18F63J11 18F63J90

18F64J11 18F64J90

18F65J10 18F65J11 18F65J15 18F65J50 18F65J90 18F65J94 18F65K22 
18F65K80 18F65K90

18F66J10 18F66J11 18F66J15 18F66J16 18F66J50 18F66J55 18F66J60 
18F66J65

18F66J90 18F66J93 18F66J94 18F66J99 18F66K22 18F66K80 18F66K90

18F67J10 18F67J11 18F67J50 18F67J60 18F67J90 18F67J93 18F67J94 
18F67K22 18F67K90

18F83J11 18F83J90

18F84J11 18F84J90

18F85J10 18F85J11 18F85J15 18F85J50 18F85J90 18F85J94 18F85K22 
18F85K90

18F86J10 18F86J11 18F86J15 18F86J16 18F86J50 18F86J55 18F86J60 
18F86J65

18F86J72 18F86J90 18F86J93 18F86J94 18F86J99 18F86K22 18F86K90

18F87J10 18F87J11 18F87J50 18F87J60 18F87J72 18F87J90 18F87J93 
18F87J94 18F87K22 18F87K90

18F95J94 18F96J60 18F96J65 18F96J94 18F96J99

18F97J60 18F97J94

18F242 18F248 18F252 18F258

18F442 18F448 18F452 18F458

18F1220 18F1230

18F1320 18F1330

18F2220 18F2221

18F2320 18F2321 18F2331

18F2410 18F2420 18F2423 18F2431 18F2439 18F2450 18F2455 18F2458 
18F2480

18F2510 18F2515 18F2520 18F2523 18F2525 18F2539 18F2550 18F2553 
18F2580 18F2585

18F2610 18F2620 18F2680 18F2682 18F2685

18F4220 18F4221

18F4320 18F4321 18F4331

18F4410 18F4420 18F4423 18F4431 18F4439 18F4450 18F4455 18F4458 
18F4480

18F4510 18F4515 18F4520 18F4523 18F4525 18F4539 18F4550 18F4553 
18F4580 18F4585

18F4610 18F4620 18F4680 18F4682 18F4685

18F6310 18F6390 18F6393

18F6410 18F6490 18F6493

18F6520 18F6525 18F6527 18F6585

18F6620 18F6621 18F6622 18F6627 18F6628 18F6680

18F6720 18F6722 18F6723

18F8310 18F8390 18F8393

18F8410 18F8490 18F8493

18F8520 18F8525 18F8527 18F8585

18F8620 18F8621 18F8622 18F8627 18F8628 18F8680

18F8720 18F8722 18F8723

18LF13K22 18LF13K50

18LF14K22 18LF14K50

18LF23K22 18LF24J10 18LF24J11 18LF24J50 18LF24K22 18LF24K50

18LF25J10 18LF25J11 18LF25J50 18LF25K22 18LF25K50 18LF25K80

18LF26J11 18LF26J13 18LF26J50 18LF26J53 18LF26K22 18LF26K80

18LF27J13 18LF27J53

18LF43K22

18LF44J10 18LF44J11 18LF44J50 18LF44K22

18LF45J10 18LF45J11 18LF45J50 18LF45K22 18LF45K50 18LF45K80

18LF46J11 18LF46J13 18LF46J50 18LF46J53 18LF46K22 18LF46K80

18LF47J13 18LF47J53

18LF65K80

18LF66K80

18LF242 18LF248 18LF252 18LF258

18LF442 18LF448 18LF452 18LF458

18LF1220 18LF1230

18LF1320 18LF1330

18LF2220 18LF2221

18LF2320 18LF2321 18LF2331

18LF2410 18LF2420 18LF2423 18LF2431 18LF2439 18LF2450 18LF2455 
18LF2458 18LF2480

18LF2510 18LF2515 18LF2520 18LF2523 18LF2525 18LF2539 18LF2550 
18LF2553 18LF2580 18LF2585

18LF2610 18LF2620 18LF2680 18LF2682 18LF2685

18LF4220 18LF4221

18LF4320 18LF4321 18LF4331

18LF4410 18LF4420 18LF4423 18LF4431 18LF4439 18LF4450 18LF4455 
18LF4458 18LF4480

18LF4510 18LF4515 18LF4520 18LF4523 18LF4525 18LF4539 18LF4550 
18LF4553 18LF4580 18LF4585

18LF4610 18LF4620 18LF4680 18LF4682 18LF4685

18LF6310 18LF6390 18LF6393

18LF6410 18LF6490 18LF6493

18LF6520 18LF6525 18LF6527 18LF6585

18LF6620 18LF6621 18LF6622 18LF6627 18LF6628 18LF6680

18LF6720 18LF6722 18LF6723

18LF8310 18LF8390 18LF8393

18LF8410 18LF8490 18LF8493

18LF8520 18LF8525 18LF8527 18LF8585

18LF8620 18LF8621 18LF8622 18LF8627 18LF8628 18LF8680

18LF8720 18LF8722 18LF8723 





An up-to-date list of supported devices is also available via 
'sdcc -mpic16 -plist'.

4.7.1 Global Options

PIC16 port supports the standard command line arguments as 
supposed, with the exception of certain cases that will be 
mentioned in the following list:

  --callee-savesPIC16!Options!--callee-saves See -
  -all-callee-saves

  --use-non-freePIC16!Options!--use-non-free Make non-free device 
  headers and libraries available in the compiler's search paths 
  (implicit -I and -L options).

4.7.2 Port Specific OptionsOptions PIC16

The port specific options appear after the global options in the 
sdcc --help output.

4.7.2.1 Code Generation Options

These options influence the generated assembler code.

  --pstack-model=[model] Used in conjunction with the command 
  above. Defines the stack model to be used, valid stack models 
  are:


  small Selects small stack model. 8 bit stack and frame 
  pointers. Supports 256 bytes stack size.

  large Selects large stack model. 16 bit stack and frame 
  pointers. Supports 65536 bytes stack size.

  --pno-banksel Do not generate BANKSEL assembler directives.

  --extended Enable extended instruction set/literal offset 
  addressing mode. Use with care!

4.7.2.2 Optimization Options

  --obanksel=n Set optimization level for inserting BANKSELs.



  0 no optimization

  1 checks previous used register and if it is the same then does 
  not emit BANKSEL, accounts only for labels.

  2 tries to check the location of (even different) symbols and 
  removes BANKSELs if they are in the same bank. 
Important: There might be problems if the linker script has data 
  sections across bank borders!

  --denable-peeps Force the usage of peepholes. Use with care.

  --no-optimize-goto Do not use (conditional) BRA instead of 
  GOTO.

  --optimize-cmp Try to optimize some compares.

  --optimize-df Analyze the dataflow of the generated code and 
  improve it.

4.7.2.3 Assembling Options

  --asm= Sets the full path and name of an external assembler to 
  call.

  --mplab-comp MPLABPIC16!MPLAB compatibility option. Currently 
  only suppresses special gpasm directives.

4.7.2.4 Linking Options

  --link= Sets the full path and name of an external linker to 
  call.

  --preplace-udata-with=[kword] Replaces the default udata 
  keyword for allocating unitialized data variables with [kword]. 
  Valid keywords are: "udata_acs", "udata_shr", "udata_ovr".

  --ivt-loc=n Place the interrupt vector table at address n. 
  Useful for bootloaders.

  --nodefaultlibs Do not link default libraries when linking.

  --use-crt= Use a custom run-time module instead of the default 
  (crt0i).

  --no-crt Don't link the default run-time modules

4.7.2.5 Debugging Options

Debugging options enable extra debugging information in the 
output files.

  --debug-xtra Similar to --debug--debug, but dumps more 
  information.

  --debug-ralloc Force register allocator to dump <source>.d file 
  with debugging information. <source> is the name of the file 
  being compiled.

  --pcode-verbose Enable pcode debugging information in 
  translation.

  --calltree Dump call tree in .calltree file.

  --gstack Trace push/pops for stack pointer overflow.

4.7.3 Environment Variables

There is a number of environmental variables that can be used 
when running SDCC to enable certain optimizations or force a 
specific program behaviour. these variables are primarily for 
debugging purposes so they can be enabled/disabled at will.

Currently there is only two such variables available:

  OPTIMIZE_BITFIELD_POINTER_GETPIC16!Environment variables!OPTIMIZEBITFIELDPOINTERGET
  SDCC!Environment variables!OPTIMIZEBITFIELDPOINTERGET (PIC16) 
  When this variable exists, reading of structure bit-fields is 
  optimized by directly loading FSR0 with the address of the 
  bit-field structure. Normally SDCC will cast the bit-field 
  structure to a bit-field pointer and then load FSR0. This step 
  saves data ram and code space for functions that make heavy use 
  of bit-fields. (i.e., 80 bytes of code space are saved when 
  compiling malloc.c with this option). 

  NO_REG_OPTPIC16!Environment variables!NOREGOPTSDCC!Environment variables!NOREGOPT
   Do not perform pCode registers optimization. This should be 
  used for debugging purposes. If bugs in the pcode optimizer are 
  found, users can benefit from temporarily disabling the 
  optimizer until the bug is fixed.

4.7.4 Preprocessor MacrosPreprocessor!PIC16 Macros

PIC16PIC16 port defines the following preprocessor macros while 
translating a source.



+---------------------------------------------+------------------------------------------------------------------------------------------+
|                   Macro                     |                                       Description                                        |
+---------------------------------------------+------------------------------------------------------------------------------------------+
+---------------------------------------------+------------------------------------------------------------------------------------------+
|    __SDCC_pic16SDCC!Defines!__SDCCpic16     |                                   Port identification                                    |
+---------------------------------------------+------------------------------------------------------------------------------------------+
|     pic18fxxxxPIC16!Defines!pic18fxxxx      | MCU Identification. xxxx is the microcontrol identification 
number, i.e. 452, 6620, etc |
+---------------------------------------------+------------------------------------------------------------------------------------------+
|     __18FxxxxPIC16!Defines!pic18fxxxx       |                            MCU Identification (same as above)                            |
+---------------------------------------------+------------------------------------------------------------------------------------------+
| STACK_MODEL_nnnPIC16!Defines!STACKMODELnnn  |           nnn = SMALL or LARGE respectively according to the stack model 
used           |
+---------------------------------------------+------------------------------------------------------------------------------------------+


In addition the following macros are defined when calling 
assembler:



+-------------------+------------------------------------------------------------------------------------------+
|      Macro        |                                       Description                                        |
+-------------------+------------------------------------------------------------------------------------------+
+-------------------+------------------------------------------------------------------------------------------+
|    __18Fxxxx      | MCU Identification. xxxx is the microcontrol identification 
number, i.e. 452, 6620, etc |
+-------------------+------------------------------------------------------------------------------------------+
| __SDCC_MODEL_nnn  |      nnn = SMALL or LARGE respectively according to the memory model 
used for SDCC      |
+-------------------+------------------------------------------------------------------------------------------+
| STACK_MODEL_nnn   |           nnn = SMALL or LARGE respectively according to the stack model 
used           |
+-------------------+------------------------------------------------------------------------------------------+


4.7.5 Directories

PIC16PIC16 port uses the following directories for searching 
header files and libraries.




+----------------------------+--------------------------+------------+----------------+
|         Directory          |       Description        |   Target   | Command prefix |
+----------------------------+--------------------------+------------+----------------+
+----------------------------+--------------------------+------------+----------------+
| PREFIX/sdcc/include/pic16  |  PIC16 specific headers  |  Compiler  |       -I       |
+----------------------------+--------------------------+------------+----------------+
|   PREFIX/sdcc/lib/pic16    | PIC16 specific libraries |   Linker   |       -L       |
+----------------------------+--------------------------+------------+----------------+


If the --use-non-free--use-non-free command line option is 
specified, non-free directories are searched:




+-------------------------------------+-----------------------------------+------------+----------------+
|             Directory               |            Description            |   Target   | Command prefix |
+-------------------------------------+-----------------------------------+------------+----------------+
+-------------------------------------+-----------------------------------+------------+----------------+
| PREFIX/sdcc/non-free/include/pic16  |  PIC16 specific non-free headers  |  Compiler  |       -I       |
+-------------------------------------+-----------------------------------+------------+----------------+
|   PREFIX/sdcc/non-free/lib/pic16    | PIC16 specific non-free libraries |   Linker   |       -L       |
+-------------------------------------+-----------------------------------+------------+----------------+


4.7.6 Pragmas<subsec:PIC16_Pragmas>

The PIC16PIC16 port currently supports the following pragmas:

  stackPIC16!Pragmas!pragma stack This forces the code generator 
  to initialize the stack & frame pointers at a specific address. 
  This is an ad hoc solution for cases where no STACK directive 
  is available in the linker script or gplink is not instructed 
  to create a stack section.
The stack pragma should be used only once in a project. Multiple 
  pragmas may result in indeterminate behaviour of the program.[footnote:
The old format (ie. #pragma stack 0x5ff) is deprecated and will 
cause the stack pointer to cross page boundaries (or even exceed 
the available data RAM) and crash the program. Make sure that 
stack does not cross page boundaries when using the SMALL stack 
model.
]
The format is as follows:

#pragma stack bottom_address [stack_size]


bottom_address is the lower bound of the stack section. The stack 
pointer initially will point at address 
(bottom_address+stack_size-1).

Example:



/* initializes stack of 100 bytes at RAM address 0x200 */

#pragma stack 0x200 100

If the stack_size field is omitted then a stack is created with 
the default size of 64. This size might be enough for most 
programs, but its not enough for operations with deep function 
nesting or excessive stack usage.

  codePIC16!Pragmas!pragma code Force a function to a static 
  FLASH address.

Example:



/* place function test_func at 0x4000 */

#pragma code test_func 0x4000



  libraryPIC16!Pragmas!pragma library instructs the linker to use 
  a library module.
Usage:

#pragma library module_name

module_name can be any library or object file (including its 
path). Note that there are four reserved keywords which have 
special meaning. These are:



+----------+-----------------------------+----------------+
| Keyword  | Description                 | Module to link |
+----------+-----------------------------+----------------+
+----------+-----------------------------+----------------+
| ignore   | ignore all library pragmas  | (none)         |
+----------+-----------------------------+----------------+
|    c     | link the C library          | libc18f.lib    |
+----------+-----------------------------+----------------+
|  math    | link the Math libarary      | libm18f.lib    |
+----------+-----------------------------+----------------+
|   io     | link the I/O library        | libio18f*.lib  |
+----------+-----------------------------+----------------+
|  debug   | link the debug library      | libdebug.lib   |
+----------+-----------------------------+----------------+

* is the device number, i.e. 452 for PIC18F452 MCU.

This feature allows for linking with specific libraries without 
having to explicit name them in the command line. Note that the 
ignore keyword will reject all modules specified by the library 
pragma.

  udataPIC16!Pragmas!pragma udata The pragma udata instructs the 
  compiler to emit code so that linker will place a variable at a 
  specific memory bank.

Example:



/* places variable foo at bank2 */

#pragma udata bank2 foo

char foo;

In order for this pragma to work extra SECTION directives should 
be added in the .lkr script. In the following example a sample 
.lkr file is shown:



// Sample linker script for the PIC18F452 processor

LIBPATH .

CODEPAGE   NAME=vectors    START=0x0            END=0x29          
 PROTECTED

CODEPAGE   NAME=page       START=0x2A           END=0x7FFF

CODEPAGE   NAME=idlocs     START=0x200000       END=0x200007      
 PROTECTED

CODEPAGE   NAME=config     START=0x300000       END=0x30000D      
 PROTECTED

CODEPAGE   NAME=devid      START=0x3FFFFE       END=0x3FFFFF      
 PROTECTED

CODEPAGE   NAME=eedata     START=0xF00000       END=0xF000FF      
 PROTECTED

ACCESSBANK NAME=accessram  START=0x0            END=0x7F



DATABANK   NAME=gpr0       START=0x80           END=0xFF

DATABANK   NAME=gpr1       START=0x100          END=0x1FF

DATABANK   NAME=gpr2       START=0x200          END=0x2FF

DATABANK   NAME=gpr3       START=0x300          END=0x3FF

DATABANK   NAME=gpr4       START=0x400          END=0x4FF

DATABANK   NAME=gpr5       START=0x500          END=0x5FF

ACCESSBANK NAME=accesssfr  START=0xF80          END=0xFFF         
 PROTECTED



SECTION    NAME=CONFIG     ROM=config



SECTION    NAME=bank0      RAM=gpr0       # these SECTION 
directives

SECTION    NAME=bank1      RAM=gpr1       # should be added to 
link

SECTION    NAME=bank2      RAM=gpr2       # section name 'bank?' 
with

SECTION    NAME=bank3      RAM=gpr3       # a specific DATABANK 
name

SECTION    NAME=bank4      RAM=gpr4

SECTION    NAME=bank5      RAM=gpr5

The linker will recognise the section name set in the pragma 
statement and will position the variable at the memory bank set 
with the RAM field at the SECTION line in the linker script file.

  configPIC16!Pragmas!pragma config The pragma config instructs 
  the compiler to emit config directive.
The format is as follows:

#pragma config setting=value [, setting=value]



Multiple settings may be defined on a single line, separated by 
commas. Settings for a single configuration byte may also be 
defined on separate lines. 

Example:



#pragma config 
CP0=OFF,OSCS=ON,OSC=LP,BOR=ON,BORV=25,WDT=ON,WDTPS=128,CCP2MUX=ON

#pragma config STVR=ON 

4.7.7 Header Files and Libraries<subsec:PIC16_Header-Files-and-Libraries>

Pic device specific header and c source files are automatically 
generated from MPLAB include files, which are published by 
Microchip with a special requirement that they are only to be 
used with authentic Microchip devices. This requirement prevents 
to publish generated header and c source files under the GPL 
compatible license, so they are located in the non-free directory 
(see section [subsec:Search-Paths]). In order to include them in 
include and library search paths, the --use-non-free--use-non-free
 command line option should be defined.

NOTE: the compiled code, which use non-free pic device specific 
libraries, is not GPL compatible!

4.7.8 Header Files<subsec:PIC16_Header-Files>

There is one main header filePIC16!Header files that can be 
included to the source files using the pic16PIC16 port. That file 
is the pic18fregs.h. This header file contains the definitions 
for the processor special registers, so it is necessary if the 
source accesses them. It can be included by adding the following 
line in the beginning of the file:

#include <pic18fregs.h>

The specific microcontroller is selected within the pic18fregs.h 
automatically, so the same source can be used with a variety of 
devices.

4.7.9 Libraries<subsec:pic16Libraries>

The librariesPIC16!Libraries that PIC16PIC16 port depends on are 
the microcontroller device libraries which contain the symbol 
definitions for the microcontroller special function registers. 
These libraries have the format pic18fxxxx.lib, where xxxx is the 
microcontroller identification number. The specific library is 
selected automatically by the compiler at link stage according to 
the selected device.

Libraries are created with gplib which is part of the gputils 
package http://sourceforge.net/projects/gputils.

  Building the libraries

Before using SDCC/pic16 there are some libraries that need to be 
compiled. This process is done automatically if gputils are found 
at SDCC's compile time. Should you require to rebuild the pic16 
libraries manually (e.g. in order to enable output of float 
valuesprintf()!PIC16 Floating point support via printf(), see 
below), these are the steps required to do so under Linux or Mac 
OS X (cygwin might work as well, but is untested):

cd device/lib/pic16

./configure.gnu

cd ..

make model-pic16

su -c 'make install'     # install the libraries, you need the 
root password

cd ../..

If you need to install the headers too, do:

cd device/include

su -c 'make install'     # install the headers, you need the root 
password

  Output of float values via printf()

The library is normally built without support for displaying 
float values, only <NO FLOAT><NO FLOAT>printf()!PIC16 floating point support
 will appear instead of the value. To change this, rebuild the 
library as stated above, but call ./configure.gnu --enable-floats 
instead of just ./configure.gnu. Also make sure that at least 
libc/stdio/vfprintf.c is actually recompiled, e.g. by touching it 
after the configure run or deleting its .o file.

The more common approach of compiling vfprintf.c manually with 
-DUSE_FLOATS=1 should also work, but is untested.

4.7.10 Adding New Devices to the Port

Adding support for a new 16bit PIC MCU requires the following 
steps:

1. Create picDEVICE.c and picDEVICE.h from pDEVICE.inc using
perl /path/to/sdcc/support/scripts/inc2h-pic16.pl \
/path/to/gputils/header/pDEVICE.inc

2. mv picDEVICE.h /path/to/sdcc/device/non-free/include/pic16

3. mv picDEVICE.c /path/to/sdcc/device/non-free/lib/pic16/libdev

4. Either


  (a) add the new device to 
    /path/to/sdcc/device/lib/pic16/libio/*.ignore to suppress 
    building any of the I/O libraries for the new device[footnote:
In fact, the .ignore files are only used when auto-generating 
Makefile.am using the .../libio/mkmk.sh script.
], or

  (b) add the device (family) to 
    /path/to/sdcc/support/scripts/pic18fam-h-gen.pl to assign I/O 
    styles, run the pic18fam-h-gen.pl script to generate 
    pic18fam.h.gen, replace your existing pic18fam.h with the 
    generated file, and (if required) implement new I/O styles in 
    /path/to/sdcc/device/include/pic16/{adc,i2c,usart}.h and 
    /path/to/sdcc/device/lib/pic16/libio/*/*.

5. Edit /path/to/sdcc/device/include/pic16/pic18fregs.h
The file format is self-explanatory, just add
#elif defined(picDEVICE)
#include <picDEVICE.h>
at the right place (keep the file sorted, please).

6. Edit /path/to/sdcc/device/include/pic16devices.txt
Copy and modify an existing entry or create a new one and insert 
  it at the correct place (keep the file sorted, please).

7. ( cd /path/to/sdcc/device/non-free/lib/pic16 && sh update.sh )

8. Recompile the pic16 libraries as described in [subsec:pic16Libraries]
   or just configure and build sdcc again from scratch 
  (recommended).

4.7.11 Memory Models

The following memory models are supported by the PIC16 port:

• small model

• large model

Memory model affects the default size of pointers within the 
source. The sizes are shown in the next table:



+-----------------------------------------++--------------+-------------+
| Pointer sizes according to memory model || small model  | large model |
+-----------------------------------------++--------------+-------------+
+-----------------------------------------++--------------+-------------+
|              code pointers              ||   16-bits    |   24-bits   |
+-----------------------------------------+               +-------------+
+-----------------------------------------++--------------+-------------+
|              data pointers              ||   16-bits    |   16-bits   |
+-----------------------------------------++--------------+-------------+


It is advisable that all sources within a project are compiled 
with the same memory model. If one wants to override the default 
memory model, this can be done by declaring a pointer as far or 
near. Far selects large memory model's pointers, while near 
selects small memory model's pointers.

The standard device libraries (see [subsec:PIC16_Header-Files]) 
contain no reference to pointers, so they can be used with both 
memory models.

4.7.12 Stack

The stackPIC16!stack implementation for the PIC16 port uses two 
indirect registers, FSR1 and FSR2.

  FSR1 is assigned as stack pointer

  FSR2 is assigned as frame pointer

The following stack models are supported by the PIC16 port

• small model

• large model

Small model means that only the FSRxL byte is used to access 
stack and frame, while large uses both FSRxL and FSRxH registers. 
The following table shows the stack/frame pointers sizes 
according to stack model and the maximum space they can address:



+------------------------------------------------------++---------+---------+
| Stack & Frame pointer sizes according to stack model || small   |  large  |
+------------------------------------------------------++---------+---------+
+------------------------------------------------------++---------+---------+
|                  Stack pointer FSR1                  || 8-bits  | 16-bits |
+------------------------------------------------------++---------+---------+
|                  Frame pointer FSR2                  || 8-bits  | 16-bits |
+------------------------------------------------------++---------+---------+


Large stack model is currently not working properly throughout 
the code generator. So its use is not advised. Also there are 
some other points that need special care:

1. Do not create stack sections with size more than one physical 
  bank (that is 256 bytes)

2. Stack sections should no cross physical bank limits (i.e. 
  #pragma stack 0x50 0x100)

These limitations are caused by the fact that only FSRxL is 
modified when using SMALL stack model, so no more than 256 bytes 
of stack can be used. This problem will disappear after LARGE 
model is fully implemented.

4.7.13 Functions

In addition to the standard SDCC function keywords, PIC16PIC16 
port makes available two more:

  __wparamPIC16!wparam Use the WREG to pass one byte of the first 
  function argument. This improves speed but you may not use this 
  for functions with arguments that are called via function 
  pointers, otherwise the first byte of the first parameter will 
  get lost. Usage:

void func_wparam(int a) __wparam

{

    /* WREG hold the lower part of a */

    /* the high part of a is stored in FSR2+2 (or +3 for large 
stack model) */

...

}

  __shadowregsPIC16!shadowregs When entering/exiting an ISR, it 
  is possible to take advantage of the PIC18F hardware shadow 
  registers which hold the values of WREG, STATUS and BSR 
  registers. This can be done by adding the keyword __shadowregs 
  before the __interrupt keyword in the function's header.

void isr_shadow(void) __shadowregs __interrupt (1)

{

...

}

__shadowregs instructs the code generator not to store/restore 
WREG, STATUS, BSR when entering/exiting the ISR.

4.7.14 Function return values

Return values from functions are placed to the appropriate 
registers following a modified Microchip policy optimized for 
SDCC. The following table shows these registers:



+-----------+----------------------------------------+
|   size    |          destination register          |
+-----------+----------------------------------------+
+-----------+----------------------------------------+
|  8 bits   |                  WREG                  |
+-----------+----------------------------------------+
| 16 bits   |               PRODL:WREG               |
+-----------+----------------------------------------+
| 24 bits   |            PRODH:PRODL:WREG            |
+-----------+----------------------------------------+
| 32 bits   |         FSR0L:PRODH:PRODL:WREG         |
+-----------+----------------------------------------+
| >32 bits  | on stack, FSR0 points to the beginning |
+-----------+----------------------------------------+


4.7.15 Interrupts

An interruptPIC16!interrupt service routine (ISR) is declared 
using the __interrupt keyword.

void isr(void) __interrupt (n)

{

...

}

n is the interrupt number, which for PIC18F devices can be:



+----+---------------------------+--------------------------+
| n  |     Interrupt Vector      | Interrupt Vector Address |
+----+---------------------------+--------------------------+
+----+---------------------------+--------------------------+
| 0  |       RESET vector        |         0x000000         |
+----+---------------------------+--------------------------+
| 1  | HIGH priority interrupts  |         0x000008         |
+----+---------------------------+--------------------------+
| 2  | LOW priority interrupts   |         0x000018         |
+----+---------------------------+--------------------------+


When generating assembly code for ISR the code generator places a 
goto instruction at the Interrupt Vector Address which points at 
the generated ISR. This single GOTO instruction is part of an 
automatically generated interrupt entry point function. The 
actual ISR code is placed as normally would in the code space. 
Upon interrupt request, the GOTO instruction is executed which 
jumps to the ISR code. When declaring interrupt functions as 
_naked this GOTO instruction is not generated. The whole 
interrupt functions is therefore placed at the Interrupt Vector 
Address of the specific interrupt. This is not a problem for the 
LOW priority interrupts, but it is a problem for the RESET and 
the HIGH priority interrupts because code may be written at the 
next interrupt's vector address and cause indeterminate program 
behaviour if that interrupt is raised.[footnote:
This is not a problem when

1. this is a HIGH interrupt ISR and LOW interrupts are disabled 
  or not used.

2. when the ISR is small enough not to reach the next interrupt's 
  vector address.
]

n may be omitted. This way a function is generated similar to an 
ISR, but it is not assigned to any interrupt.

When entering an interrupt, currently the PIC16PIC16 port 
automatically saves the following registers:

• WREG

• STATUS

• BSR

• PROD (PRODL and PRODH)

• FSR0 (FSR0L and FSR0H)

These registers are restored upon return from the interrupt 
routine.[footnote:
NOTE that when the _naked attribute is specified for an interrupt 
routine, then NO registers are stored or restored.
]

4.7.16 Generic Pointers

Generic pointers are implemented in PIC16 port as 3-byte (24-bit) 
types. There are 3 types of generic pointers currently 
implemented data, code and eeprom pointers. They are 
differentiated by the value of the 7th and 6th bits of the upper 
byte:



+-----------------+-----------+---------+-----------------------------------------------------------------------+
|  pointer type   |  7th bit  | 6th bit |    rest of the pointer       description                              |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|      data       |     1     |    0    |  uuuuuu uuuuxxxx xxxxxxxx    a 12-bit data pointer in data RAM memory |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|      code       |     0     |    0    |  uxxxxx xxxxxxxx xxxxxxxx    a 21-bit code pointer in FLASH memory    |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
|     eeprom      |     0     |    1    |  uuuuuu uuuuuuxx xxxxxxxx    a 10-bit eeprom pointer in EEPROM memory |
+-----------------+-----------+---------+-----------------------------------------------------------------------+
| (unimplemented) |     1     |    1    |  xxxxxx xxxxxxxx xxxxxxxx    unimplemented pointer type               |
+-----------------+-----------+---------+-----------------------------------------------------------------------+


Generic pointer are read and written with a set of library 
functions which read/write 1, 2, 3, 4 bytes.

4.7.17 Configuration Bits

Configuration bits (also known as fuses) can be configured using 
one of two methods:

• using #pragma config (see section [subsec:PIC16_Pragmas]), 
  which is a preferred method for the new code. Example:

#pragma config 
CP0=OFF,OSCS=ON,OSC=LP,BOR=ON,BORV=25,WDT=ON,WDTPS=128,CCP2MUX=ON

#pragma config STVR=ON

• using `__code' and `__at' modifiers. This method is deprecated. 
  Possible options should be ANDed and can be found in your 
  processor header file. Example for PIC18F2550:

#include <pic18fregs.h> //Contains config addresses and options

static __code char __at(__CONFIG1L) configword1l =
  _USBPLL_CLOCK_SRC_FROM_96MHZ_PLL_2_1L &

  _PLLDIV_NO_DIVIDE__4MHZ_INPUT__1L & [...];
static __code char __at(__CONFIG1H) configword1h = [...];
static __code char __at(__CONFIG2L) configword2l = [...];
//More configuration words

Mixing both methods is not allowed and throws an error message ”
mixing __CONFIG and CONFIG directives”.

4.7.18 PIC16 C Libraries

4.7.18.1 Standard I/O Streams

In the stdio.h the type FILE is defined as:

typedef char * FILE;

This type is the stream type implemented I/O in the PIC18F 
devices. Also the standard input and output streams are declared 
in stdio.h:

extern FILE * stdin;

extern FILE * stdout;

The FILE type is actually a generic pointer which defines one 
more type of generic pointers, the stream pointer. This new type 
has the format:



+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
| pointer type |  <7:6>  | <5>  | <4>  | <3:0> |  rest of the pointer    descrption                                          |
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+
|    stream    |   00    |  1   |  0   | nnnn  |   uuuuuuuu uuuuuuuu     upper byte high nubble is 0x2n, the rest are zeroes |
+--------------+---------+------+------+-------+-----------------------------------------------------------------------------+


Currently implemented there are 3 types of streams defined:



+---------------+-------------+---------+----------------------------------------------------+
| stream type   |   value     | module  |                    description                     |
+---------------+-------------+---------+----------------------------------------------------+
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_USART  | 0x200000UL  | USART   |  Writes/Reads characters via the USART peripheral  |
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_MSSP   | 0x210000UL  |  MSSP   |  Writes/Reads characters via the MSSP peripheral   |
+---------------+-------------+---------+----------------------------------------------------+
| STREAM_USER   | 0x2f0000UL  | (none)  | Writes/Reads characters via used defined functions |
+---------------+-------------+---------+----------------------------------------------------+


The stream identifiers are declared as macros in the stdio.h 
header.

In the libc library there exist the functions that are used to 
write to each of the above streams. These are

  __stream_usart_putchar writes a character at the USART stream

  __stream_mssp_putchar writes a character at the MSSP stream

  putchar dummy function. This writes a character to a user 
  specified manner.

In order to increase performance putchar is declared in stdio.h 
as having its parameter in WREG (it has the __wparam keyword). In 
stdio.h exists the macro PUTCHAR(arg) that defines the putchar 
function in a user-friendly way. arg is the name of the variable 
that holds the character to print. An example follows:

#include <pic18fregs.h>
#include <stdio.h>

PUTCHAR( c )

{

    PORTA = c;    /* dump character c to PORTA */

}

void main(void)

{

    stdout = STREAM_USER;    /* this is not necessary, since 
stdout points

                              * by default to STREAM_USER */

    printf (”This is a printf test\n”);

}



4.7.18.2 Printing functions

PIC16 contains an implementation of the printf-familyprintf()!PIC16
 of functions. There exist the following functions:

extern unsigned int sprintf(char *buf, char *fmt, ...);

extern unsigned int vsprintf(char *buf, char *fmt, va_list ap);



extern unsigned int printf(char *fmt, ...);

extern unsigned int vprintf(char *fmt, va_lista ap);



extern unsigned int fprintf(FILE *fp, char *fmt, ...);

extern unsigned int vfprintf(FILE *fp, char *fmt, va_list ap);

For sprintf and vsprintf buf should normally be a data pointer 
where the resulting string will be placed. No range checking is 
done so the user should allocate the necessary buffer. For 
fprintf and vfprintf fp should be a stream pointer (i.e. stdout, 
STREAM_MSSP, etc...).

4.7.18.3 Signals

The PIC18F family of microcontrollers supports a number of 
interrupt sources. A list of these interrupts is shown in the 
following table:



+--------------+----------------------------++--------------+---------------------------------------+
| signal name  |        description         || signal name  |              description              |
+--------------+----------------------------++--------------+---------------------------------------+
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_RB       |   PORTB change interrupt   || SIG_EE       | EEPROM/FLASH write complete interrupt |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT0     |  INT0 external interrupt   || SIG_BCOL     |        Bus collision interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT1     |  INT1 external interrupt   || SIG_LVD      |     Low voltage detect interrupt      |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_INT2     |  INT2 external interrupt   || SIG_PSP      |     Parallel slave port interrupt     |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_CCP1     |   CCP1 module interrupt    || SIG_AD       |   AD convertion complete interrupt    |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_CCP2     |   CCP2 module interrupt    || SIG_RC       |        USART receive interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR0     |  TMR0 overflow interrupt   || SIG_TX       |       USART transmit interrupt        |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR1     |  TMR1 overflow interrupt   || SIG_MSSP     |    SSP receive/transmit interrupt     |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR2     | TMR2 matches PR2 interrupt ||              |                                       |
+--------------+----------------------------++--------------+---------------------------------------+
| SIG_TMR3     |  TMR3 overflow interrupt   ||              |                                       |
+--------------+----------------------------++--------------+---------------------------------------+


The prototypes for these names are defined in the header file 
signal.h.

In order to simplify signal handling, a number of macros is 
provided:

DEF_INTHIGH(name) begin the definition of the interrupt dispatch 
table for high priority interrupts. name is the function name to 
use.

DEF_INTLOW(name) begin the definition of the interrupt dispatch 
table for low priority interrupt. name is the function name to 
use.

DEF_HANDLER(sig,handler) define a handler for signal sig.

END_DEF end the declaration of the dispatch table.

Additionally there are two more macros to simplify the 
declaration of the signal handler:

SIGHANDLER(handler) this declares the function prototype for the 
handler function.

SIGHANDLERNAKED(handler) same as SIGHANDLER() but declares a 
naked function.

An example of using the macros above is shown below:

#include <pic18fregs.h>

#include <signal.h>

DEF_INTHIGH(high_int)

DEF_HANDLER(SIG_TMR0, _tmr0_handler)

DEF_HANDLER(SIG_BCOL, _bcol_handler)

END_DEF

SIGHANDLER(_tmr0_handler)

{

  /* action to be taken when timer 0 overflows */

}

SIGHANDLERNAKED(_bcol_handler)

{

  __asm

    /* action to be taken when bus collision occurs */

    retfie

 __endasm;

}

NOTES: Special care should be taken when using the above scheme:

• do not place a colon (;) at the end of the DEF_* and END_DEF 
  macros.

• when declaring SIGHANDLERNAKED handler never forget to use 
  retfie for proper returning.

4.7.19 PIC16 Port – Tips

Here you can find some general tips for compiling programs with 
SDCC/pic16.

4.7.19.1 Stack size

The default stackPIC16!stack size (that is 64 bytes) probably is 
enough for many programs. One must take care that when there are 
many levels of function nesting, or there is excessive usage of 
stack, its size should be extended. An example of such a case is 
the printf/sprintf family of functions. If you encounter problems 
like not being able to print integers, then you need to set the 
stack size around the maximum (256 for small stack model). The 
following diagram shows what happens when calling printf to print 
an integer:

printf () --> ltoa () --> ultoa () --> divschar ()

It is should be understood that stack is easily consumed when 
calling complicated functions. Using command line arguments like 
--fomit-frame-pointer might reduce stack usage by not creating 
unnecessary stack frames. Other ways to reduce stack usage may 
exist.

4.7.20 Known Bugs

4.7.20.1 Extended Instruction Set

The PIC16 port emits code which is incompatible with the extended 
instruction set available with many newer devices. Make sure to 
always explicitly disable it, usually using:

• #pragma config XINST=OFF

or deprecated:

• static __code char __at(__CONFIG4L) conf4l = /* more flags & */ 
  _XINST_OFF_4L;

Some devices (namely 18f2455, 18f2550, 18f4455, and 18f4550) use 
_ENHCPU_OFF_4L instead of _XINST_OFF_4L.

4.7.20.2 Regression Tests

The PIC16 port currently passes most but not all of the tests in 
SDCC's regression testRegression test (PIC16) suite (see section [sec:Quality-control]
), thus no automatic regression tests are currently performed for 
the PIC16 target.

Debugging

There are several approaches to debugging your code. This chapter 
is meant to show your options and to give detail on some of them:

When writing your code:

• write your code with debugging in mind (avoid duplicating code, 
  put conceptually similar variables into structs, use structured 
  code, have strategic points within your code where all 
  variables are consistent, ...)

• run a syntax-checking tool like splintsplint (syntax checking tool)
  lint (syntax checking tool) (see --more-pedantic [lyx:more-pedantic-SPLINT]
  ) over the code.

• for the high level code use a C-compiler (like f.e. GCC) to 
  compile run and debug the code on your host. See (see -
  -more-pedantic [lyx:more-pedantic-SPLINT]) on how to handle 
  syntax extensions like __xdata, __at(), ... 

• use another C-compiler to compile code for your target. Always 
  an option but not recommended:) And not very likely to help 
  you. If you seriously consider walking this path you should at 
  least occasionally check portability of your code. Most 
  commercial compiler vendors will offer an evaluation version so 
  you can test compile your code or snippets of your code.

Debugging on a simulator:

• there is a separate section about SDCDB (section [cha:Debugging-with-SDCDB]
  ) below.

• or (8051 specific) use a free open source/commercial simulator 
  which interfaces to the AOMFAOMF, AOMF51 file (see [OMF file]) 
  optionally generated by SDCC.

Debugging On-target: 

• use a MCU port pin to serially output debug data to the RS232 
  port of your host. You'll probably want some level shifting 
  device typically involving a MAX232 or similar IC. If the 
  hardware serial port of the MCU is not available search for 
  'Software UART' in your favourite search machine.

• use an on-target monitor. In this context a monitor is a small 
  program which usually accepts commands via a serial line and 
  allows to set program counter, to single step through a program 
  and read/write memory locations. For the 8051 good examples of 
  monitors are paulmon and cmon51 (see section [sec:Related-open-source-tools]
  ).

• toggle MCU port pins at strategic points within your code and 
  use an oscilloscope. A digital oscilloscopeOscilloscope with 
  deep trace memory is really helpful especially if you have to 
  debug a realtime application. If you need to monitor more pins 
  than your oscilloscope provides you can sometimes get away with 
  a small R-2R network. On a single channel oscilloscope you 
  could for example monitor 2 push-pull driven pins by connecting 
  one via a 10 k\Omega resistor and the other one by a 5 k\Omega 
  resistor to the oscilloscope probe (check output drive 
  capability of the pins you want to monitor). If you need to 
  monitor many more pins a logic analyzer will be handy.

• use an ICE (in circuit emulatorICE (in circuit emulator)). 
  Usually very expensive. And very nice to have too. And usually 
  locks you (for years...) to the devices the ICE can emulate. 

• use a remote debugger. In most 8-bit systems the symbol 
  information is not available on the target, and a complete 
  debugger is too bulky for the target system. Therefore usually 
  a debugger on the host system connects to an on-target 
  debugging stub which accepts only primitive commands. 
Terms to enter into your favourite search engine could be 'remote 
  debugging', 'gdb stub' or 'inferior debugger'. (is there one?)

• use an on target hardware debugger. Some of the more modern 
  MCUs include hardware support for setting break points and 
  monitoring/changing variables by using dedicated hardware pins. 
  This facility doesn't require additional code to run on the 
  target and usually doesn't affect runtime behaviour until a 
  breakpoint is hit. For the mcs51 most hardware debuggers use 
  the AOMFAOMF, AOMF51 file (see [OMF file]) as input file. 

Last not least:

• if you are not familiar with any of the following terms you're 
  likely to run into problems rather sooner than later: volatile, 
  atomic, memory map, overlay. As an embedded programmer you have 
  to know them so why not look them up before you have problems?)

• tell someone else about your problem (actually this is a 
  surprisingly effective means to hunt down the bug even if the 
  listener is not familiar with your environment). As 'failure to 
  communicate' is probably one of the job-induced deformations of 
  an embedded programmer this is highly encouraged.

5.1 Debugging with SDCDB<cha:Debugging-with-SDCDB>SDCDB (debugger)
   

SDCC is distributed with a source level debuggerDebugger. The 
debugger uses a command line interface, the command repertoire of 
the debugger has been kept as close to gdbgdb (the GNU debugger) 
as possible. The configuration and build process is part of the 
standard compiler installation, which also builds and installs 
the debugger in the target directory specified during 
configuration. The debugger allows you debug BOTH at the C source 
and at the ASM source level.

5.1.1 Compiling for Debugging

The --debug--debug option must be specified for all files for 
which debug information is to be generated. The compiler 
generates a .adb file for each of these files. The linker creates 
the .cdb<file>.cdb file from the .adb<file>.adb files and the 
address information. This .cdb is used by the debugger.

5.1.2 How the Debugger Works

When the --debug option is specified the compiler generates extra 
symbol information some of which are put into the assembler 
source and some are put into the .adb file. Then the linker 
creates the .cdb file from the individual .adb files with the 
address information for the symbols. The debugger reads the 
symbolic information generated by the compiler & the address 
information generated by the linker. It uses the SIMULATOR 
(Daniel's S51) to execute the program, the program execution is 
controlled by the debugger. When a command is issued for the 
debugger, it translates it into appropriate commands for the 
simulator. (Currently SDCDM only connects to the simulator but 
newcdb at http://ec2drv.sourceforge.net/ is an effort to connect 
directly to the hardware.) 

5.1.3 Starting the Debugger SDCDB

The debugger can be started using the following command line. 
(Assume the file you are debugging has the file name foo).

sdcdb foo

The debugger will look for the following files.

• foo.c - the source file.

• foo.cdb - the debugger symbol information file.

• foo.ihx - the Intel hex formatIntel hex format object file.

5.1.4 SDCDB Command Line Options

• --directory=<source file directory> this option can used to 
  specify the directory search list. The debugger will look into 
  the directory list specified for source, cdb & ihx files. The 
  items in the directory list must be separated by ':', e.g. if 
  the source files can be in the directories /home/src1 and 
  /home/src2, the --directory option should be -
  -directory=/home/src1:/home/src2. Note there can be no spaces 
  in the option. 

• -cd <directory> - change to the <directory>.

• -fullname - used by GUI front ends.

• -cpu <cpu-type> - this argument is passed to the simulator 
  please see the simulator docs for details.

• -X <Clock frequency > this options is passed to the simulator 
  please see the simulator docs for details.

• -s <serial port file> passed to simulator see the simulator 
  docs for details.

• -S <serial in,out> passed to simulator see the simulator docs 
  for details.

• -k <port number> passed to simulator see the simulator docs for 
  details.

5.1.5 SDCDB Debugger Commands

As mentioned earlier the command interface for the debugger has 
been deliberately kept as close the GNU debugger gdb, as 
possible. This will help the integration with existing graphical 
user interfaces (like ddd, xxgdb or xemacs) existing for the GNU 
debugger. If you use a graphical user interface for the debugger 
you can skip this section.

  break [line | file:line | function | file:function]

Set breakpoint at specified line or function:

sdcdb>break 100 
sdcdb>break foo.c:100
sdcdb>break funcfoo
sdcdb>break foo.c:funcfoo

  clear [line | file:line | function | file:function ]

Clear breakpoint at specified line or function:

sdcdb>clear 100
sdcdb>clear foo.c:100
sdcdb>clear funcfoo
sdcdb>clear foo.c:funcfoo

  continue

Continue program being debugged, after breakpoint.

  finish

Execute till the end of the current function.

  delete [n]

Delete breakpoint number 'n'. If used without any option clear 
ALL user defined break points.

  info [break | stack | frame | registers ]

• info break - list all breakpoints

• info stack - show the function call stack.

• info frame - show information about the current execution 
  frame.

• info registers - show content of all registers.

  step

Step program until it reaches a different source line. Note: 
pressing <return> repeats the last command.

  next

Step program, proceeding through subroutine calls.

  run

Start debugged program.

  ptype variable 

Print type information of the variable.

  print variable

print value of variable.

  file filename

load the given file name. Note this is an alternate method of 
loading file for debugging.

  frame

print information about current frame.

  set srcmode

Toggle between C source & assembly source.

  ! simulator command

Send the string following '!' to the simulator, the simulator 
response is displayed. Note the debugger does not interpret the 
command being sent to the simulator, so if a command like 'go' is 
sent the debugger can loose its execution context and may display 
incorrect values.

  quit

"Watch me now. Iam going Down. My name is Bobby Brown"

5.1.6 Interfacing SDCDB with DDD



The portable network graphics File http://sdcc.sourceforge.net/wiki_images/ddd_example.png
 shows a screenshot of a debugging session with DDDDDD (debugger) 
(Unix only) on a simulated 8032. The debugging session might not 
run as smoothly as the screenshot suggests. The debugger allows 
setting of breakpoints, displaying and changing variables, single 
stepping through C and assembler code. 
The source was compiled with 

sdcc --debug ddd_example.c 

and DDD was invoked with 

ddd -debugger "sdcdb -cpu 8032 ddd_example"



5.1.7 Interfacing SDCDB with XEmacsXEmacsEmacs

Two files (in emacs lisp) are provided for the interfacing with 
XEmacs, sdcdb.el and sdcdbsrc.el. These two files can be found in 
the $(prefix)/bin directory after the installation is complete. 
These files need to be loaded into XEmacs for the interface to 
work. This can be done at XEmacs startup time by inserting the 
following into your '.xemacs' file (which can be found in your 
HOME directory): 

(load-file sdcdbsrc.el)

.xemacs is a lisp file so the () around the command is REQUIRED. 
The files can also be loaded dynamically while XEmacs is running, 
set the environment variable 'EMACSLOADPATH' to the installation 
bin directory (<installdir>/bin), then enter the following 
command ESC-x load-file sdcdbsrc. To start the interface enter 
the following command:

ESC-x sdcdbsrc

You will prompted to enter the file name to be debugged.

The command line options that are passed to the simulator 
directly are bound to default values in the file sdcdbsrc.el. The 
variables are listed below, these values maybe changed as 
required.

• sdcdbsrc-cpu-type '51

• sdcdbsrc-frequency '11059200

• sdcdbsrc-serial nil

The following is a list of key mapping for the debugger 
interface.

 
;; Current Listing ::
;;key              binding                      Comment
;;---              -------                      -------
;; 
;; n               sdcdb-next-from-src          SDCDB next 
command
;; b               sdcdb-back-from-src          SDCDB back 
command
;; c               sdcdb-cont-from-src          SDCDB continue 
command
;; s               sdcdb-step-from-src          SDCDB step 
command
;; ?               sdcdb-whatis-c-sexp          SDCDB 
ptypecommand for data at
;;                                               buffer point
;; x               sdcdbsrc-delete              SDCDB Delete all 
breakpoints if no arg
;;                                               given or delete 
arg (C-u arg x)
;; m               sdcdbsrc-frame               SDCDB Display 
current frame if no arg,
;;                                               given or display 
frame arg
;;                                               buffer point
;; !               sdcdbsrc-goto-sdcdb          Goto the SDCDB 
output buffer
;; p               sdcdb-print-c-sexp           SDCDB print 
command for data at
;;                                               buffer point
;; g               sdcdbsrc-goto-sdcdb          Goto the SDCDB 
output buffer
;; t               sdcdbsrc-mode                Toggles Sdcdbsrc 
mode (turns it off)
;;
;; C-c C-f         sdcdb-finish-from-src        SDCDB finish 
command
;;
;; C-x SPC         sdcdb-break                  Set break for 
line with point
;; ESC t           sdcdbsrc-mode                Toggle Sdcdbsrc 
mode
;; ESC m           sdcdbsrc-srcmode             Toggle list mode
;;

5.2 Debugging with other debuggers (e.g. GDB): ELF / DWARF

For some ports, SDCC can create ELF binaries with DWARF debug 
information. This can e.g. be used for on-target debugging on 
STM8 using OpenOCD and GDB. To do so, compile with –debug 
–out-fmt-elf. Note that –out-fmt-elf needs to be specified both 
when compiling (to generate the debug info in DWARF rather than 
CDB format) and linking (to get an ELF binary instead of Intel 
Hex).

TIPS

Here are a few guidelines that will help the compiler generate 
more efficient code, some of the tips are specific to this 
compiler others are generally good programming practice.

• Use the smallest data type to represent your data-value. If it 
  is known in advance that the value is going to be less than 256 
  then use an 'unsigned char' instead of a 'short' or 'int'. 
  Please note, that ANSI C requires both signed and unsigned 
  chars to be promoted to 'signed int'promotion to signed int[margin:
 !
] before doing any operation. This promotiontype promotion<type promotion>
   can be omitted, if the result is the same. The effect of the 
  promotion rules together with the sign-extension is often 
  surprising:


  unsigned char uc = 0xfe;
if (uc * uc < 0) /* this is true! */
{
    ....
}

  uc * uc is evaluated as (int) uc * (int) uc = (int) 0xfe * 
  (int) 0xfe = (int) 0xfc04 = -1024.
Another one:

  (unsigned char) -12 / (signed char) -3 = ...

  No, the result is not 4:

  (int) (unsigned char) -12 / (int) (signed char) -3 =
(int) (unsigned char) 0xf4 / (int) (signed char) 0xfd =
(int) 0x00f4 / (int) 0xfffd =
(int) 0x00f4 / (int) 0xfffd =
(int) 244 / (int) -3 =
(int) -81 = (int) 0xffaf;

  Don't complain, that gcc gives you a different result. gcc uses 
  32 bit ints, while SDCC uses 16 bit ints. Therefore the results 
  are different.
From ”comp.lang.c FAQ”:

  If well-defined overflow characteristics are important and 
  negative values are not, or if you want to steer clear of 
  sign-extension problems when manipulating bits or bytes, use 
  one of the corresponding unsigned types. (Beware when mixing 
  signed and unsigned values in expressions, though.)
Although character types (especially unsigned char) can be used 
  as "tiny" integers, doing so is sometimes more trouble than 
  it's worth, due to unpredictable sign extension and increased 
  code size.

• Use unsigned when it is known in advance that the value is not 
  going to be negative. This helps especially if you are doing 
  division or multiplication, bit-shifting or are using an array 
  index.

• NEVER jump into a LOOP.

• Declare the variables to be locallocal variables whenever 
  possible, especially loop control variables (induction).

• Have a look at the assembly listing to get a ”feeling” for the 
  code generation.

6.1 Porting code from or to other compilers<sec:Porting-code-to-other-compilers>

• check whether endiannessEndianness of the compilers differs and 
  adapt where needed.

• check the device specific header filesHeader filesInclude files 
  for compiler specific syntax. Eventually include the file 
  <compiler.hcompiler.h (include file)> 
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/device/include/mcs51/compiler.h
   to allow using common header files. (see f.e. cc2510fx.h 
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/device/include/mcs51/cc2510fx.h
  ).

• check whether the startup code contains the correct 
  initialization (watchdogwatchdog, peripherals).

• check whether the sizes of short, int, long match.

• check if some 16 or 32 bit hardware registers require a 
  specific addressing order (least significant or most 
  significant byte first) and adapt if needed (first and last 
  relate to time and not to lower/upper memory location here, so 
  this is not the same as endianness).

• check whether the keyword volatilevolatile is used where 
  needed. The compilers might differ in their optimization 
  characteristics (as different versions of the same compiler 
  might also use more clever optimizations this is good idea 
  anyway). See section [subsec:Common-interrupt-pitfall-volatile]
  .

• check that the compilers are not told to suppress warnings.

• check and convert compiler specific extensions (interrupts, 
  memory areas, pragmas etc.).

• check for differences in type promotion. Especially check for 
  math operations on char or unsigned char variables. For the 
  sake of C99 compatibility SDCC will probably promote these to 
  int more often than other compilers. Eventually insert explicit 
  casts to (char) or (unsigned char). Also check that the ~ 
  operator~ Operator is not used on bitbit variables, use the ! 
  operator instead. See sections [type promotion] and [sec:Compatibility-with-previous]
  .

• check the assembly code generated for interrupt routines (f.e. 
  for calls to possibly non-reentrant library functions).

• check whether timing loops result in proper timing (or 
  preferably consider a rewrite of the code with timer based 
  delays instead).

• check for differences in printf parametersprintf()!parameters 
  (some compilers push (va_argvararg, vaarg) char variables as 
  int others push them as char. See section [sec:Compatibility-with-previous]
  ). Provide a putchar()printf()!putchar() function if needed.

• check the resulting memory mapMemory map. Usage of different 
  memory spaces: code, stack, data (for mcs51/ds390 additionally 
  idata, pdata, xdata). Eventually check if unexpected library 
  functions are included.

6.2 ToolsTools included in the distribution


+---------------------------+-----------------------------------------------------------------------+----------------------+
| Name                      | Purpose                                                               | Directory            |
+---------------------------+-----------------------------------------------------------------------+----------------------+
+---------------------------+-----------------------------------------------------------------------+----------------------+
| as2gbmap.py               | sdas map to rrgb map and no$gmb sym file format converter             | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| cinc2h.pl                 | gpasm inc to c header file converter                                  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| gen_known_bugs.pl         | generate knownbugs.html                                               | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| keil2sdcc.pl              | Keil header Header filesInclude files to SDCC header file 
converter  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| makebin                   | Intel Hex to binary and GameBoy binay format converter                | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| mcs51-disasm.pl           | disassembler to the mcs51 instructions contained hex files            | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| mh2h.c                    | header file conversion                                                | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| optimize_pic16devices.pl  | optimizes or unoptimizes the pic16devices.txt file                    | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| packihx                   | Intel Hex packer packihx (tool)                                       | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| pic14-header-parser.pl    | helper to realization of peripheral-handling (PIC14)                  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| pic16-header-parser.pl    | helper to realization of peripheral-handling (PIC16)                  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| pic16fam-h-gen.pl         | helper to realization of peripheral-handling (PIC14)                  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| pic18fam-h-gen.pl         | helper to realization of peripheral-handling (PIC16)                  | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| repack_release.sh         | repack sdcc to release package                                        | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdas390                   | assembler                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdas6808                  | assembler                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdas8051                  | assembler                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdasgb                    | assembler                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdasz80                   | assembler                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdcc_cygwin_mingw32       | cross compile the sdcc with mingw32 under Cygwin                      | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdcc_mingw32              | cross compile the sdcc with mingw32                                   | sdcc/support/scripts |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| SDCDB                     | simulator                                                             | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdld                      | linker                                                                | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdld6808                  | linker                                                                | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdldgb                    | linker                                                                | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| sdldz80                   | linker                                                                | sdcc/bin             |
+---------------------------+-----------------------------------------------------------------------+----------------------+
| uCsimuCsim                | simulator for various architectures                                   | sdcc/sim/ucsim       |


6.3 DocumentationDocumentation included in the distribution


+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| Subject / Title                                                                                                                           | Filename / Where to get                                                                                                  |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| SDCC Compiler User Guide                                                                                                                  | You're reading it right now         online at:
http://sdcc.sourceforge.net/doc/sdccman.pdf                               |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| Changelog of SDCC                                                                                                                         | sdcc/Changelog         online at:
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/ChangeLog                                |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| ASXXXXsdas (sdasgb, sdas6808, sdas8051, sdasz80)Assembler documentation
 Assemblers and
ASLINKsdldLinker documentation Relocating Linker  | sdcc/sdas/doc/asmlnk.txt         online at:
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/sdas/doc/asmlnk.txt            |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| SDCC regression testRegression test                                                                                                       | test_suite_spec        online at:

http://sdcc.sourceforge.net/wiki/index.php/Proposed_Test_Suite_Design                 |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| Various notes                                                                                                                             | sdcc/doc/*         online at:
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/doc/                                         |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| Notes on debugging with SDCDBSDCDB (debugger)                                                                                             | sdcc/debugger/README         online at:
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/debugger/README                    |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| uCsimuCsim Software simulator for microcontrollers                                                                                        | sdcc/sim/ucsim/doc/index.html         online at:

http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/sim/ucsim/doc/index.html |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| Temporary notes on the pic16PIC16 port                                                                                                    | sdcc/src/pic16/NOTES         online at:
http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/src/pic16/NOTES                    |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+
| SDCC internal documentation (debugging file format)

                                                                                     | sdcc/doc/cdbfileformat.pdf         online at:
http://sdcc.sourceforge.net/wiki/index.php/CDB_File_Format                 |
+-------------------------------------------------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------------------------------------------+


6.4 Communication online at SourceForge


+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| Subject / Title                                                                                      | Note                                            | Link                                                         |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| wikiwikiCommunication!wiki                                                                           |                                                 | http://sdcc.sourceforge.net/wiki/                            |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| sdcc-user mailing listmailing listCommunication!Mailing lists                                        | around 650 subscribers mid 2009                 | https://lists.sourceforge.net/mailman/listinfo/sdcc-user     |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| sdcc-devel mailing list                                                                              |                                                 | https://lists.sourceforge.net/mailman/listinfo/sdcc-devel    |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| help forumCommunication!Forums                                                                       | similar scope as sdcc-user mailing list         | http://sourceforge.net/p/sdcc/discussion/1865                |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| open discussion forum                                                                                |                                                 | http://sourceforge.net/p/sdcc/discussion/1864                |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| trackers (bug tracker, feature requests, patches, support 
requests, webdocs)Communication!Trackers  |                                                 | http://sourceforge.net/p/sdcc/_list/tickets                  |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+
| rss feedRSS feedCommunication!RSS feed                                                               | stay tuned with most (not all) sdcc activities  | http://sourceforge.net/export/rss2_keepsake.php?group_id=599 |
+------------------------------------------------------------------------------------------------------+-------------------------------------------------+--------------------------------------------------------------+


With a sourceforge account you can ”monitor”Communication!Monitor 
forums and trackers, so that you automatically receive mail on 
changes. You can digg out earlier communication by using the 
search function http://sourceforge.net/search/?group_id=599.

6.5 Related open source tools<sec:Related-open-source-tools>Related tools


+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| Name                                        | Purpose                                                                                            | Where to get                                                                         |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| gpsimgpsim (pic simulator)                  | PIC simulator                                                                                      | http://www.dattalo.com/gnupic/gpsim.html                                             |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| gputilsgputils (pic tools)                  | GNU PIC utilities                                                                                  | http://sourceforge.net/projects/gputils                                              |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| flP5                                        | PIC programmer                                                                                     | http://freshmeat.net/projects/flp5/                                                  |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| ec2drv/newcdb                               | Tools for Silicon Laboratories JTAG debug adapter, partly based 
on SDCDB (Unix only)              | http://sourceforge.net/projects/ec2drv                                               |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| indentindent (source formatting tool)       | Formats C source - Master of the white spaces                                                      | http://directory.fsf.org/GNU/indent.html                                             |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| srecordsrecord (bin, hex, ... tool)         | Object file conversion, checksumming, ...                                                          | http://sourceforge.net/projects/srecord                                              |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| objdumpobjdump (tool)                       | Object file conversion, ...                                                                        | Part of binutils (should be there anyway)                                            |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| cmon51                                      | 8051 monitor (hex up-/download, single step, disassemble)                                          | http://sourceforge.net/projects/cmon51                                               |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| doxygendoxygen (source documentation tool)  | Source code documentation system                                                                   | http://www.doxygen.org                                                               |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| kdevelop                                    | IDE (has anyone tried integrating SDCC & SDCDB? Unix only)                                         | http://www.kdevelop.org                                                              |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| paulmon                                     | 8051 monitor (hex up-/download, single step, disassemble)                                          | http://www.pjrc.com/tech/8051/paulmon2.html                                          |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| splintsplint (syntax checking tool)         | Statically checks c sources (see [lyx:more-pedantic-SPLINT])                                       | http://www.splint.org                                                                |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| dddDDD (debugger)                           | Debugger, serves nicely as GUI to SDCDBSDCDB (debugger) (Unix 
only)                               | http://www.gnu.org/software/ddd/                                                     |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| d52d52d52 (disassembler)                    | Disassembler, can count instruction cyclesinstruction cycles (count)
, use with options -pnd       | http://www.8052.com/users/disasm/                                                    |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+
| cmakecmake                                  | Cross platform build system, generates MakefilesMakefile and 
project workspacesproject workspace  | http://www.cmake.org and a dedicated wiki entry: http://www.cmake.org/Wiki/CmakeSdcc |
+---------------------------------------------+----------------------------------------------------------------------------------------------------+--------------------------------------------------------------------------------------+


6.6 Related documentation / recommended reading


+--------------------+--------------------------------------------+----------------------------------------------------------------+
| Name               | Subject / Title                            | Where to get                                                   |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
+--------------------+--------------------------------------------+----------------------------------------------------------------+
| c-refcard.pdf      | C Reference CardC Reference card, 2 pages  | http://refcards.com/refcards/c/index.html                      |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
| c-faq              | C-FAQC FAQ                                 | http://www.c-faq.com                                           |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
| ISO/IEC 9899:TC2   | ”C-Standard”                               | http://www.open-std.org/jtc1/sc22/wg14/www/standards.html#9899 |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
| ISO/IEC DTR 18037  | ”Extensions for Embedded C”                | http://www.open-std.org/jtc1/sc22/wg14/www/docs/n1021.pdf      |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
|                    | Latest datasheet of target CPU             | vendor                                                         |
+--------------------+--------------------------------------------+----------------------------------------------------------------+
|                    | Revision history of datasheet              | vendor                                                         |
+--------------------+--------------------------------------------+----------------------------------------------------------------+


6.7 Application notes specifically for SDCC

SDCC makes no claims about the completeness of this list and 
about up-to-dateness or correctness of the application notesApplication notes
.



+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Vendor                         | Subject / Title                                                                                                      | Where to get                                                                                  |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Maxim / Dallas                 | Using the SDCC Compiler for the DS80C400DS80C400                                                                     | http://pdfserv.maxim-ic.com/en/an/AN3346.pdf                                                  |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Maxim / Dallas                 | Using the Free SDCC C Compiler to Develop Firmware for the 
DS89C420/430/440/450DS89C4x0 Family of Microcontrollers  | http://pdfserv.maxim-ic.com/en/an/AN3477.pdf                                                  |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Silicon Laboratories / Cygnal  | Integrating SDCC 8051 Tools Into The Silicon Labs IDEIDE                                                             | 
http://www.silabs.com/public/documents/tpub_doc/anote/Microcontrollers/en/an198.pdf          |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Ramtron / Goal Semiconductor   | Interfacing SDCC to Syn and Textpad                                                                                  | 
http://www.ramtron.com/doc/Products/Microcontroller/Support_Tools.asp                        |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Ramtron / Goal Semiconductor   | Installing and Configuring SDCC and Crimson Editor                                                                   | 
http://www.ramtron.com/doc/Products/Microcontroller/Support_Tools.asp                        |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+
| Texas Instruments              | MSC12xx Programming with SDCC                                                                                        | 
http://focus.ti.com/general/docs/lit/getliterature.tsp?literatureNumber=sbaa109&fileType=pdf |
+--------------------------------+----------------------------------------------------------------------------------------------------------------------+-----------------------------------------------------------------------------------------------+


6.8 Some Questions

Some questions answered, some pointers given - it might be time 
to in turn ask you some questions: 

• can you solve your project with the selected microcontroller? 
  Would you find out early or rather late that your target is too 
  small/slow/whatever? Can you switch to a slightly better device 
  if it doesn't fit?

• should you solve the problem with an 8 bit CPU? Or would a 
  16/32 bit CPU and/or another programming language be more 
  adequate? Would an operating system on the target device help?

• if you solved the problem, will the marketing department be 
  happy?

• if the marketing department is happy, will customers be happy?

• if you're the project manager, marketing department and maybe 
  even the customer in one person, have you tried to see the 
  project from the outside?

• is the project done if you think it is done? Or is just that 
  other interface/protocol/feature/configuration/option missing? 
  How about website, manual(s), internationali(z|s)ation, 
  packaging, labels, 2nd source for components, electromagnetic 
  compatability/interference, documentation for production, 
  production test software, update mechanism, patent issues?

• is your project adequately positioned in that magic triangle: 
  fame, fortune, fun?

Maybe not all answers to these questions are known and some 
answers may even be no, nevertheless knowing these questions may 
help you to avoid burnout[footnote:
burnout is bad for electronic devices, programmers and motorcycle 
tyres
]. Chances are you didn't want to hear some of them...

SupportSupport

SDCC has grown to be a large project. The compiler alone (without 
the preprocessor, assembler and linker) is well over 150,000 
lines of code (blank stripped). The open source nature of this 
project is a key to its continued growth and support. You gain 
the benefit and support of many active software developers and 
end users. Is SDCC perfect? No, that's why we need your help. The 
developers take pride in fixing reported bugs. You can help by 
reporting the bugs and helping other SDCC users. There are lots 
of ways to contribute, and we encourage you to take part in 
making SDCC a great software package. 

The SDCC project is hosted on the SDCC SourceForge site at http://sourceforge.net/projects/sdcc
. You'll find the complete set of mailing listsMailing list(s), 
forums, bug reporting system, patch submissionPatch submission 
system, wiki, rss-feed, downloaddownload area and Subversion code 
repositorySubversion code repository there.

7.1 Reporting BugsBug reportingReporting bugsCommunication!Bug report

The recommended way of reporting bugs is using the infrastructure 
of the SourceForge site. You can follow the status of bug reports 
there and have an overview about the known bugs.

Bug reports are automatically forwarded to the developer mailing 
list and will be fixed ASAP. When reporting a bug, it is very 
useful to include a small test program (the smaller the better) 
which reproduces the problem. If you can isolate the problem by 
looking at the generated assembly code, this can be very helpful. 
Compiling your program with the --dumpall--dumpall option can 
sometimes be useful in locating optimization problems. When 
reporting a bug please make sure you:

1. Attach the code you are compiling with SDCC. 

2. Specify the exact command you use to run SDCC, or attach your 
  Makefile. 

3. Specify the SDCC version (type "sdcc -v"), your platform, and 
  operating system. 

4. Provide an exact copy of any error message or incorrect 
  output. 

5. Put something meaningful in the subject of your message.

Please attempt to include these 5 important parts, as applicable, 
in all requests for support or when reporting any problems or 
bugs with SDCC. Though this will make your message lengthy, it 
will greatly improve your chance that SDCC users and developers 
will be able to help you. Some SDCC developers are frustrated by 
bug reports without code provided that they can use to reproduce 
and ultimately fix the problem, so please be sure to provide 
sample code if you are reporting a bug! 

Please have a short check that you are using a recent version of 
SDCC and the bug is not yet known. This is the link for reporting 
bugs: http://sourceforge.net/p/sdcc/bugs/. With SDCC on average 
having more than 200 downloadsdownload on SourceForge per day[footnote:
220 daily downloads on average Jan-Sept 2006 and about 150 daily 
downloads between 2002 and 2005. This does not include other 
methods of distribution.
] there must be some users. So it's not exactly easy to find a 
new bug. If you find one we need it: reporting bugs is good.

7.2 Requesting Features<subsec:Requesting-Features>Feature request
  Requesting featuresCommunication!Feature request

Like bug reports feature requests are forwarded to the developer 
mailing list. This is the link for requesting features: http://sourceforge.net/p/sdcc/feature-requests/
.

7.3 Submitting patchesCommunication!Patch submission

Like bug reports contributed patches are forwarded to the 
developer mailing list. This is the link for submitting patchesPatch submission
: http://sourceforge.net/p/sdcc/patches/.

You need to specify some parameters to the diff command for the 
patches to be useful. If you modified more than one file a patch 
created f.e. with ”diff -Naur unmodified_directory 
modified_directory >my_changes.patch” will be fine, otherwise ”
diff -u sourcefile.c.orig sourcefile.c >my_changes.patch” will 
do.

7.4 Getting Help

These links should take you directly to the Mailing lists http://sourceforge.net/p/sdcc/mailman/sdcc-user/
[footnote:
Traffic on sdcc-devel and sdcc-user is about 100 mails/month each 
not counting automated messages (mid 2003)
] and the Forums http://sourceforge.net/p/sdcc/discussion/, listsMailing list(s)
Communication!Mailing lists and forums are archived and 
searchable so if you are lucky someone already had a similar 
problem. While mails to the lists themselves are delivered 
promptly their web front end on SourceForge sometimes shows a 
severe time lag (up to several weeks), if you're seriously using 
SDCC please consider subscribing to the lists.

7.5 ChangeLog

You can follow the status of the Subversion versionversion of 
SDCC by watching the ChangelogChangelog in the Subversion 
repository http://svn.code.sf.net/p/sdcc/code/trunk/sdcc/ChangeLog
.

7.6 Subversion Source Code Repository

The output of sdcc --version or the filenames of the snapshot 
versions of SDCC include date and its SubversionSubversion code repository
 number. Subversion allows to download the source of recent or 
previous versions http://sourceforge.net/p/sdcc/code/8805/tree/ 
(by number or by date).

7.7 Release policyRelease policy

Starting with version 2.4.0 SDCC in 2004 uses a time-based 
release schedule with one official release usually during the 
first half of the year.

The last digit of an official release is zero. Additionally there 
are daily snapshots available at http://sdcc.sourceforge.net/snap.php
, and you can always build the very last version from the source 
code available at Sourceforge http://sdcc.sourceforge.net/snap.php#Source
. The SDCC WikiwikiSDCC Wiki at http://sdcc.sourceforge.net/wiki/ 
also holds some information about past and future releases.

7.8 Quality control<sec:Quality-control>Quality control

The compiler is passed through daily snapshot build compile and 
build checks. The so called regression testsRegression test check 
that SDCC itself compiles flawlessly on several host platforms 
(i386, Opteron, 64 bit Alpha, ppc64, Mac OS X on ppc and i386, 
Solaris on Sparc) and checks the quality of the code generated by 
SDCC by running the code for several target platforms through 
simulators. The regression test suite comprises about 1000 files 
which expand to more than 1500 test cases which include about 
7000 tests. A large number of tests from the GCC test suite is 
included in this. The results of these tests are published daily 
on SDCC's snapshot page (click on the red or green symbols on the 
right side of http://sdcc.sourceforge.net/snap.php).

You'll find the test code in the directory 
sdcc/support/regression. You can run these tests manually by 
running make in this directory (or f.e. ”make test-mcs51” if you 
don't want to run the complete tests). The test code might also 
be interesting if you want to look for examplesExamples checking 
corner cases of SDCC or if you plan to submit patchesPatch submission
.

The PIC14 port uses a different set of regression tests Regression test (PIC14)
, you'll find them in the directory sdcc/src/regression.

7.9 ExamplesExamples

You'll find some small examples in the directory 
sdcc/device/examples/. More examples and libraries are available 
at The SDCC Open Knowledge Resource http://sdccokr.dl9sec.de/ web 
site or at http://www.pjrc.com/tech/8051/.



7.10 Use of SDCC in Education

In short: highly encouraged[footnote:
the phrase "use in education" might evoke the association "only 
fit for use in education". This connotation is not intended but 
nevertheless risked as the licensing of SDCC makes it difficult 
to offer educational discounts
]. If your rationales are to:

1. give students a chance to understand the complete steps of 
  code generation

2. have a curriculum that can be extended for years. Then you 
  could use an FPGA board as target and your curriculum will 
  seamlessly extend from logic synthesis 
  (http://www.opencores.org opencores.org, Oregano http://www.oregano.at/ip/ip01.htm
  ), over assembly programming, to C to FPGA compilers (FPGAC http://sourceforge.net/projects/fpgac/
  ) and to C.

3. be able to insert excursions about skills like using a 
  revision control system, submitting/applying patches, using a 
  type-setting (as opposed to word-processing) engine LyX/LaTeX, 
  using SourceForge http://sourceforge.net/, following some 
  netiquette http://en.wikipedia.org/wiki/Netiquette, 
  understanding BSD/LGPL/GPL/Proprietary licensing, growth models 
  of Open Source Software, CPU simulation, compiler regression 
  testsRegression test. 
And if there should be a shortage of ideas then you can always 
  point students to the ever-growing feature request list http://sourceforge.net/p/sdcc/feature-requests/
  .

4. not tie students to a specific host platform and instead allow 
  them to use a host platform of their choice (among them Alpha, 
  i386, i386_64, Mac OS X, Mips, Sparc, Windows and eventually 
  OLPC http://www.laptop.org)

5. not encourage students to use illegal copies of educational 
  software

6. be immune to licensing/availability/price changes of the 
  chosen tool chain

7. be able to change to a new target platform without having to 
  adopt a new tool chain

8. have complete control over and insight into the tool chain

9. make your students aware about the pros and cons of open 
  source software development

10. give back to the public as you are probably at least 
  partially publicly funded

11. give students a chance to publicly prove their skills and to 
  possibly see a world wide impact

then SDCC is probably among the first choices. Well, probably 
SDCC might be the only choice.

SDCC Technical Data

8.1 OptimizationsOptimizations

SDCC performs a host of standard optimizations in addition to 
some MCU specific optimizations. 

8.1.1 Sub-expression EliminationSubexpression elimination

The compiler does local and global common subexpression 
elimination, e.g.: 

i = x + y + 1;
j = x + y;

will be translated to

iTemp = x + y;
i = iTemp + 1;
j = iTemp;

Some subexpressions are not as obvious as the above example, 
e.g.:

a->b[i].c = 10;
a->b[i].d = 11;

In this case the address arithmetic a->b[i] will be computed only 
once; the equivalent code in C would be.

iTemp = a->b[i];
iTemp.c = 10;
iTemp.d = 11;

The compiler will try to keep these temporary variables in 
registers.

8.1.2 Dead-Code EliminationDead-code elimination

int global;

void f () {
  int i;
  i = 1;      /* dead store */
  global = 1; /* dead store */
  global = 2;
  return;
  global = 3; /* unreachable */
}

will be changed to

int global;

void f () {
  global = 2; 
}

8.1.3 Copy-PropagationCopy propagation

int f() {
  int i, j;
  i = 10;
  j = i;
  return j;
}

will be changed to 

int f() {
  int i, j;
  i = 10;
  j = 10;
  return 10;
}

Note: the dead stores created by this copy propagation will be 
eliminated by dead-code elimination.

8.1.4 Loop OptimizationsLoop optimization<subsec:Loop-Optimizations>

Two types of loop optimizations are done by SDCC loop invariant 
lifting and strength reduction of loop induction variables. In 
addition to the strength reduction the optimizer marks the 
induction variables and the register allocator tries to keep the 
induction variables in registers for the duration of the loop. 
Because of this preference of the register allocatorRegister allocation
, loop induction optimization causes an increase in register 
pressure, which may cause unwanted spilling of other temporary 
variables into the stackstack / data space. The compiler will 
generate a warning message when it is forced to allocate extra 
space either on the stack or data space. If this extra space 
allocation is undesirable then induction optimization can be 
eliminated either for the entire source file (with --noinduction 
option) or for a given function only using #pragma noinductionpragma noinduction
.

Loop Invariant:

for (i = 0 ; i < 100 ; i ++)
    f += k + l;

changed to

itemp = k + l;
for (i = 0; i < 100; i++)
    f += itemp;

As mentioned previously some loop invariants are not as apparent, 
all static address computations are also moved out of the loop.

Strength ReductionStrength reduction, this optimization 
substitutes an expression by a cheaper expression:

for (i=0;i < 100; i++)
    ar[i*5] = i*3;

changed to

itemp1 = 0;
itemp2 = 0;
for (i=0;i< 100;i++) {
    ar[itemp1] = itemp2;
    itemp1 += 5;
    itemp2 += 3;
}

The more expensive multiplicationMultiplication is changed to a 
less expensive addition.

8.1.5 Loop ReversingLoop reversing

This optimization is done to reduce the overhead of checking loop 
boundaries for every iteration. Some simple loops can be reversed 
and implemented using a “decrement and jump if not zero” 
instruction. SDCC checks for the following criterion to determine 
if a loop is reversible (note: more sophisticated compilers use 
data-dependency analysis to make this determination, SDCC uses a 
more simple minded analysis).

• The 'for' loop is of the form 

for(<symbol> = <expression>; <sym> [< | <=] <expression>; 
  [<sym>++ | <sym> += 1])
    <for body>

• The <for body> does not contain “continue” or 'break”.

• All goto's are contained within the loop.

• No function calls within the loop.

• The loop control variable <sym> is not assigned any value 
  within the loop

• The loop control variable does NOT participate in any 
  arithmetic operation within the loop.

• There are NO switch statements in the loop.

8.1.6 Algebraic Simplifications

SDCC does numerous algebraic simplifications, the following is a 
small sub-set of these optimizations.

i = j + 0;     /* changed to: */     i = j;
i /= 2;        /* for unsigned i changed to: */     i >>= 1;
i = j - j;     /* changed to: */     i = 0;
i = j / 1;     /* changed to: */     i = j;

Note the subexpressionsSubexpression given above are generally 
introduced by macro expansions or as a result of copy/constant 
propagation.

8.1.7 'switch' Statements<subsec:'switch'-Statements>switch statement

SDCC can optimize switch statements to jump tablesjump tables. It 
makes the decision based on an estimate of the generated code 
size. SDCC is quite liberal in the requirements for jump table 
generation: 

• The labels need not be in order, and the starting number need 
  not be one or zero, the case labels are in numerical sequence 
  or not too many case labels are missing.


  switch(i) {                          switch (i) {
   case 4: ...                          case 0: ...
   case 5: ...                          case 1: ...
   case 3: ...                          
   case 6: ...                          case 3: ...
   case 7: ...                          case 4: ...
   case 8: ...                          case 5: ...
   case 9: ...                          case 6: ...
   case 10: ...                         case 7: ...
   case 11: ...                         case 8: ...
}                                    }

  Both the above switch statements will be implemented using a 
  jump-table. The example to the right side is slightly more 
  efficient as the check for the lower boundary of the jump-table 
  is not needed.

• The number of case labels is not larger than supported by the 
  target architecture.

• If the case labels are not in numerical sequence ('gaps' 
  between cases) SDCC checks whether a jump table with 
  additionally inserted dummy cases is still attractive. 

• If the starting number is not zero and a check for the lower 
  boundary of the jump-table can thus be eliminated SDCC might 
  insert dummy cases 0, ... .

Switch statements which have large gaps in the numeric sequence 
or those that have too many case labels can be split into more 
than one switch statement for efficient code generation, e.g.:

switch (i) {
  case 1: ...
  case 2: ...
  case 3: ...
  case 4: ...
  case 5: ...
  case 6: ...
  case 7: ...
  case 101: ...
  case 102: ...
  case 103: ...
  case 104: ...
  case 105: ...
  case 106: ...
  case 107: ...
}

If the above switch statement is broken down into two switch 
statements

switch (i) {
  case 1: ...
  case 2: ...
  case 3: ...
  case 4: ...
  case 5: ...
  case 6: ...
  case 7: ...
}

and

switch (i) {
  case 101: ...
  case 102: ...
  case 103: ...
  case 104: ...
  case 105: ...
  case 106: ...
  case 107: ...
}

then both the switch statements will be implemented using 
jump-tables whereas the unmodified switch statement will not be.



8.1.8 Bit-shifting OperationsBit shifting.

Bit shifting is one of the most frequently used operation in 
embedded programming. SDCC tries to implement bit-shift 
operations in the most efficient way possible, e.g.:

unsigned char i;
...
i >>= 4;
...

generates the following code:

mov  a,_i
swap a
anl  a,#0x0f
mov  _i,a

Typically, SDCC will not setup a loop if the shift count is 
known. Another example:

unsigned int i;
...
i >>= 9;
...

will generate:

mov  a,(_i + 1)
mov  (_i + 1),#0x00
clr  c
rrc  a
mov  _i,a

8.1.9 Bit-rotationBit rotation

A special case of the bit-shift operation is bit rotationrotating bits
, SDCC recognizes the following expression to be a left 
bit-rotation:

unsigned  char i;           /* unsigned is needed for rotation */
...
i = ((i << 1) | (i >> 7));
...

will generate the following code:

mov  a,_i
rl   a
mov  _i,a

SDCC uses pattern matching on the parse tree to determine this 
operation.Variations of this case will also be recognized as 
bit-rotation, i.e.: 

i = ((i >> 7) | (i << 1)); /* left-bit rotation */

8.1.10 Nibble and Byte Swapping

Other special cases of the bit-shift operations are nibble or 
byte swappingswapping nibbles/bytes, SDCC recognizes the 
following expressions:

unsigned  char i;
unsigned  int j;
...
i = ((i << 4) | (i >> 4)); 
j = ((j << 8) | (j >> 8)); 

and generates a swap instruction for the nibble swappingNibble swapping
 or move instructions for the byte swappingByte swapping. The ”j” 
example can be used to convert from little to big-endian or vice 
versa. If you want to change the endianness of a signed integer 
you have to cast to (unsigned int) first.

Note that SDCC stores numbers in little-endian[footnote:
Usually 8-bit processors don't care much about endianness. This 
is not the case for the standard 8051 which only has an 
instruction to increment its dptrDPTR-datapointer so 
little-endian is the more efficient byte order.
]little-endianEndianness format (i.e. lowest order first) for 
most backends. However, the hc08, s08 and stm8 backends are 
big-endian.

8.1.11 Getting a BitAny Order Bit

It is frequently required to obtain the highest order bit of an 
integral type (long, int, short or char types). Also obtaining 
any other order bit is not uncommon. SDCC recognizes the 
following expressions to yield the highest order bit and 
generates optimized code for it, e.g.:

unsigned int gint;

foo () {
  unsigned char hob1, aob1;
  bit hob2, hob3, aob2, aob3;
  ...
  hob1 = (gint >> 15) & 1;
  hob2 = (gint >> 15) & 1;
  hob3 = gint & 0x8000;
  aob1 = (gint >> 9) & 1;
  aob2 = (gint >> 8) & 1;
  aob3 = gint & 0x0800;
  ...
}

will generate the following code:

                          61 ;  hob.c 7
000A E5*01                62         mov   a,(_gint + 1)
000C 23                   63         rl    a
000D 54 01                64         anl   a,#0x01
000F F5*02                65         mov   _foo_hob1_1_1,a
                          66 ;  hob.c 8
0011 E5*01                67         mov   a,(_gint + 1)
0013 33                   68         rlc   a
0014 92*00                69         mov   _foo_hob2_1_1,c
                          66 ;  hob.c 9
0016 E5*01                67         mov   a,(_gint + 1)
0018 33                   68         rlc   a
0019 92*01                69         mov   _foo_hob3_1_1,c
                          70 ;  hob.c 10
001B E5*01                71         mov   a,(_gint + 1)
001D 03                   72         rr    a
001E 54 01                73         anl   a,#0x01
0020 F5*03                74         mov   _foo_aob1_1_1,a
                          75 ;  hob.c 11
0022 E5*01                76         mov   a,(_gint + 1)
0024 13                   77         rrc   a
0025 92*02                78         mov   _foo_aob2_1_1,c
                          79 ;  hob.c 12
0027 E5*01                80         mov   a,(_gint + 1)
0029 A2 E3                81         mov   c,acc[3]
002B 92*03                82         mov   _foo_aob3_1_1,c

Other variations of these cases however will not be recognized. 
They are standard C expressions, so I heartily recommend these be 
the only way to get the highest order bit, (it is portable). Of 
course it will be recognized even if it is embedded in other 
expressions, e.g.:

xyz = gint + ((gint >> 15) & 1);

will still be recognized.

8.1.12 Higher Order ByteHigher Order Byte / Higher Order WordHigher Order Word

It is also frequently required to obtain a higher order byte or 
word of a larger integral type (long, int or short types). For 
mcs51, SDCC recognizes the following expressions to yield the 
higher order byte or word and generates optimized code for it, 
e.g.:

unsigned int gint;
unsigned long int glong;

foo () {
  unsigned char hob1, hob2;
  unsigned int how1, how2;
  ...
  hob1 = (gint >> 8) & 0xFF;
  hob2 = glong >> 24;
  how1 = (glong >> 16) & 0xFFFF;
  how2 = glong >> 8;
  ...
}

will generate the following code:

                          91 ;  hob.c 15
0037 85*01*06             92         mov   _foo_hob1_1_1,(_gint + 
1)
                          93 ;  hob.c 16
003A 85*05*07             94         mov   _foo_hob2_1_1,(_glong 
+ 3)
                          95 ;  hob.c 17
003D 85*04*08             96         mov   _foo_how1_1_1,(_glong 
+ 2)
0040 85*05*09             97         mov   (_foo_how1_1_1 + 
1),(_glong + 3)
0043 85*03*0A             98         mov   _foo_how2_1_1,(_glong 
+ 1)
0046 85*04*0B             99         mov   (_foo_how2_1_1 + 
1),(_glong + 2)

Again, variations of these cases may not be recognized. They are 
standard C expressions, so I heartily recommend these be the only 
way to get the higher order byte/word, (it is portable). Of 
course it will be recognized even if it is embedded in other 
expressions, e.g.:

xyz = gint + ((gint >> 8) & 0xFF);

will still be recognized.

8.1.13 Placement of Bank-Selection Instructions

For non-intrinsic named address spaces, SDCC will place the bank 
selection instructions optimally. For details see Philipp Klaus 
Krause, ”Optimal Placement of Bank Selection Instructions in 
Polynomial Time”, Proceedings of the 16th International Workshop 
on Software and Compilers for Embedded Systems, M-SCOPES ’13, pp 
23–30. Association for Computing Machinery, 2013. 

8.1.14 Lifetime-Optimal Speculative Partial Redundancy 
  Elimination

SDCC has an implementation of lifetime-optimal speculative 
partial redundancy elimination based on tree-decompositions.

8.1.15 Register Allocation<subsec:Register-Allocation>Register-Allocation

SDCC currently has two register allocators. One of them is 
optimal when optimizing for code size. This register allocator is 
used by default on all ports except for mcs51, ds390, pic14 and 
pic16. With the exception of hc08 and s08, it is also the only 
available register allocator for these ports. Even though it runs 
in polynomial time, it can be quite slow; therefore the --max-allocs-per-node
 command line option can be used for a trade-off between 
compilation speed and quality of the generated code: Lower values 
result in faster compilation, higher values can result in better 
code being generated.

It first creates a tree-decomposition of the control-flow graph, 
and then uses dynamic programming bottom-up along the 
tree-decomposition. Optimality is achieved through the use of a 
cost function, which gives cost for instructions under register 
assignments. The cost function is target-specific and has to be 
implemented for each port; in all current SDCC ports the cost 
function is integrated into code generation.

For more details on how this register allocator works, see: 
Philipp Klaus Krause, ”Optimal Register Allocation in Polynomial 
Time”, Compiler Construction - 22nd International Conference, CC 
2013, Held as Part of the European Joint Conferences on Theory 
and Practice of Software, ETAPS 2013. Proceedings, Lecture Notes 
in Computer Science, volume 7791, pp. 1-20. Springer, 2013. Also: 
Philipp Klaus Krause, ”Bytewise Register Allocation”, Proceedings 
of the 18th International Workshop on Software and Compilers for 
Embedded Systems, SCOPES ’15, pp 22–27. Association for Computing 
Machinery, 2015. 

8.1.16 Peephole Optimizer<subsec:Peephole-Optimizer>Peephole optimizer

The compiler uses a rule based, pattern matching and re-writing 
mechanism for peep-hole optimization. It is inspired by copt a 
peep-hole optimizer by Christopher W. Fraser (cwfraser @ 
microsoft.com). A default set of rules are compiled into the 
compiler, additional rules may be added with the --peep-file--peep-file
 <filename> option. The rule language is best illustrated with 
examples.

replace {
  mov %1,a
  mov a,%1
} by {
  mov %1,a
}

The above rule will change the following assemblyAssembler routines
 sequence:

mov r1,a
mov a,r1

to

mov r1,a

Note: All occurrences of a %n (pattern variable) must denote the 
same string. With the above rule, the assembly sequence:

mov r1,a
mov a,r2

will remain unmodified.

Other special case optimizations may be added by the user (via -
-peep-file option). E.g. some variants of the 8051 MCUMCS51 variants
 allow only ajmp and acall. The following two rules will change 
all ljmp and lcall to ajmp and acall

replace { lcall %1 } by { acall %1 }
replace { ljmp %1 } by { ajmp %1 }

(NOTE: from version 2.7.3 on, you can use option --acall-ajmp--acall-ajmp
, which also takes care of aligning the interrupt vectors 
properly.)


The inline-assembler code is also passed through the peep hole 
optimizer, thus the peephole optimizer can also be used as an 
assembly level macro expander. The rules themselves are MCU 
dependent whereas the rule language infra-structure is MCU 
independent. Peephole optimization rules for other MCU can be 
easily programmed using the rule language.

The syntax for a rule is as follows:

rule := replace [ restart ] '{' <assembly sequence> '\n'
                            '}' by '{' '\n'
                                <assembly sequence> '\n'
                            '}' [if <functionName> ] '\n'

<assembly sequence> := assembly instruction (each instruction 
including labels must be on a separate line).

The optimizer will apply to the rules one by one from the top in 
the sequence of their appearance, it will terminate when all 
rules are exhausted. If the 'restart' option is specified, then 
the optimizer will start matching the rules again from the top, 
this option for a rule is expensive (performance), it is intended 
to be used in situations where a transformation will trigger the 
same rule again. An example of this (not a good one, it has side 
effects) is the following rule:

replace restart {
  pop %1
  push %1 } by {
  ; nop
}

Note that the replace pattern cannot be a blank, but can be a 
comment line. Without the 'restart' option only the innermost 
'pop' 'push' pair would be eliminated, i.e.:

pop ar1
pop ar2
push ar2
push ar1

would result in:

pop ar1
; nop
push ar1

with the restart option the rule will be applied again to the 
resulting code and then all the pop-push pairs will be eliminated 
to yield:

; nop
; nop

A conditional function can be attached to a rule. Attaching rules 
are somewhat more involved, let's illustrate this with an 
example.

replace {
     ljmp %5
%2:
} by {
     sjmp %5
%2:
} if labelInRange

The optimizer does a look-up of a function name table defined in 
function callFuncByName in the source file SDCCpeeph.c, with the 
name labelInRange. If it finds a corresponding entry the function 
is called. Note there can be no parameters specified for some of 
these functions, in this case the use of %5 is crucial, since the 
function labelInRange expects to find the label in that 
particular variable (the hash table containing the variable 
bindings is passed as a parameter). If you want to code more such 
functions, take a close look at the function labelInRange and the 
calling mechanism in source file SDCCpeeph.c. Currently 
implemented are labelInRange, labelRefCount, labelRefCountChange, 
labelIsReturnOnly, xramMovcOption, portIsDS390, 24bitMode, 
notVolatile. notUsed, notSame, operandsNotRelated, 
labelJTInRange, canAssign, optimizeReturn, notUsedFrom, 
labelIsReturnOnly, operandsLiteral, labelIsUncondJump, deadMove, 
useAcallAjmp and okToRemoveSLOC.

This whole thing is a little kludgy, but maybe some day SDCC will 
have some better means. If you are looking at the peeph*.def 
files, you will see the default rules that are compiled into the 
compiler, you can add your own rules in the default set there if 
you get tired of specifying the --peep-file option.

8.2 Cyclomatic ComplexityCyclomatic complexity

Cyclomatic complexity of a function is defined as the number of 
independent paths the program can take during execution of the 
function. This is an important number since it defines the number 
test cases you have to generate to validate the function. The 
accepted industry standard for complexity number is 10, if the 
cyclomatic complexity reported by SDCC exceeds 10 you should 
think about simplification of the function logic. Note that the 
complexity level is not related to the number of lines of code in 
a function. Large functions can have low complexity, and small 
functions can have large complexity levels. 

SDCC uses the following formula to compute the complexity:


complexity = (number of edges in control flow graph) - (number of 
nodes in control flow graph) + 2;

Having said that the industry standard is 10, you should be aware 
that in some cases it be may unavoidable to have a complexity 
level of less than 10. For example if you have switch statement 
with more than 10 case labels, each case label adds one to the 
complexity level. The complexity level is by no means an absolute 
measure of the algorithmic complexity of the function, it does 
however provide a good starting point for which functions you 
might look at for further optimization.

8.3 Retargetting for other Processors

The issues for retargetting the compiler are far too numerous to 
be covered by this document. What follows is a brief description 
of each of the phases of the compiler and its MCU dependency.

• Parsing the source and building the annotated parse tree. This 
  phase is largely MCU independent (except for the language 
  extensions). Syntax & semantic checks are also done in this 
  phase, along with some initial optimizations like back patching 
  labels and the pattern matching optimizations like bit-rotation 
  etc.

• The second phase involves generating an intermediate code which 
  can be easy manipulated during the later phases. This phase is 
  entirely MCU independent. The intermediate code generation 
  assumes the target machine has unlimited number of registers, 
  and designates them with the name iTemp. The compiler can be 
  made to dump a human readable form of the code generated by 
  using the --dumpraw option.

• This phase does the bulk of the standard optimizations and is 
  also MCU independent. This phase can be broken down into 
  several sub-phases:

Break down intermediate code (iCode) into basic blocks.
Do control flow & data flow analysis on the basic blocks.
Do local common subexpression elimination, then global 
  subexpression elimination
Dead code elimination
Loop optimizations
If loop optimizations caused any changes then do 'global 
  subexpression elimination' and 'dead code elimination' again.

• This phase determines the live-ranges; by live range I mean 
  those iTemp variables defined by the compiler that still 
  survive after all the optimizations. Live range analysisLive range analysis
   is essential for register allocation, since these computation 
  determines which of these iTemps will be assigned to registers, 
  and for how long.

• Phase five is register allocation. For new ports register 
  allocator described above in [subsec:Register-Allocation] 
  should be used in most cases, since it can result in 
  substantially better code. In the old register allocator, there 
  are two parts to register allocation.

The first part I call 'register packing' (for lack of a better 
  term). In this case several MCU specific expression folding is 
  done to reduce register pressure.

The second part is more MCU independent and deals with allocating 
  registers to the remaining live ranges. A lot of MCU specific 
  code does creep into this phase because of the limited number 
  of index registers available in the 8051.

• The Code generation phase is (unhappily), entirely MCU 
  dependent and very little (if any at all) of this code can be 
  reused for other MCU. However the scheme for allocating a 
  homogenized assembler operand for each iCode operand may be 
  reused.

• As mentioned in the optimization section the peep-hole 
  optimizer is rule based system, which can reprogrammed for 
  other MCUs.

More information is available on SDCC Wikiwiki (preliminary link 
http://sdcc.sourceforge.net/wiki/index.php/SDCC_internals_and_porting
) and in the thread http://sourceforge.net/mailarchive/message.php?msg_id=13954144
 .

Compiler internalsCompiler internals

9.1 The anatomy of the compiler<subsec:The-anatomy-of>

This is an excerpt from an article published in Circuit Cellar 
Magazine in August 2000. It's outdated (the compiler is much more 
efficient now and user/developer friendly), but pretty well 
exposes the guts of it all.

The current version of SDCC can generate code for Intel 8051 and 
Z80 MCU. It is fairly easy to retarget for other 8-bit MCU. Here 
we take a look at some of the internals of the compiler. 

  ParsingParsing 

Parsing the input source file and creating an AST (Annotated 
Syntax TreeAnnotated syntax tree). This phase also involves 
propagating types (annotating each node of the parse tree with 
type information) and semantic analysis. There are some MCU 
specific parsing rules. For example the intrinsic named address 
spaces are MCU specific: While there may be an __xdata intrinsic 
named address space for 8051 there none for z80. SDCC has MCU 
specific intrinsic named address spacess, i.e. __xdata will be 
treated as a named address space when parsing 8051 C code but 
will be treated as a C identifier when parsing z80 code.

  Generating iCodeiCode

Intermediate code generation. In this phase the AST is broken 
down into three-operand form (iCode). These three operand forms 
are represented as doubly linked lists. ICode is the term given 
to the intermediate form generated by the compiler. ICode example 
section shows some examples of iCode generated for some simple C 
source functions.

  OptimizationsOptimizations.

Bulk of the target independent optimizations is performed in this 
phase. The optimizations include constant propagation, common 
sub-expression elimination, loop invariant code movement, 
strength reduction of loop induction variables and dead-code 
elimination.

  Live range analysisLive range analysis

During intermediate code generation phase, the compiler assumes 
the target machine has infinite number of registers and generates 
a lot of temporary variables. The live range computation 
determines the lifetime of each of these compiler-generated 
temporaries. A picture speaks a thousand words. ICode example 
sections show the live range annotations for each of the operand. 
It is important to note here, each iCode is assigned a number in 
the order of its execution in the function. The live ranges are 
computed in terms of these numbers. The from number is the number 
of the iCode which first defines the operand and the to number 
signifies the iCode which uses this operand last.

  Register AllocationRegister allocation

The register allocation determines the type and number of 
registers needed by each operand. In most MCUs only a few 
registers can be used for indirect addressing. In case of 8051 
for example the registers R0 & R1 can be used to indirectly 
address the internal ram and DPTR to indirectly address the 
external ram. The compiler will try to allocate the appropriate 
register to pointer variables if it can. ICode example section 
shows the operands annotated with the registers assigned to them. 
The compiler will try to keep operands in registers as much as 
possible; there are several schemes the compiler uses to do 
achieve this. When the compiler runs out of registers the 
compiler will check to see if there are any live operands which 
is not used or defined in the current basic block being 
processed, if there are any found then it will push that operand 
and use the registers in this block, the operand will then be 
popped at the end of the basic block. 

There are other MCU specific considerations in this phase. Some 
MCUs have an accumulator; very short-lived operands could be 
assigned to the accumulator instead of a general-purpose 
register.

  Code generation

Figure II gives a table of iCodeiCode operations supported by the 
compiler. The code generation involves translating these 
operations into corresponding assembly code for the processor. 
This sounds overly simple but that is the essence of code 
generation. Some of the iCode operations are generated on a MCU 
specific manner for example, the z80 port does not use registers 
to pass parameters so the SEND and RECV iCode operations will not 
be generated, and it also does not support JUMPTABLES. 


Figure II 
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| iCodeiCode                   | Operands                           | Description                                                                                                                                | C Equivalent                                                      |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '!'                          | IC_LEFT() IC_RESULT()              | NOT operation                                                                                                                              | IC_RESULT = ! IC_LEFT;                                            |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '~'                          | IC_LEFT() IC_RESULT()              | Bitwise complement of                                                                                                                      | IC_RESULT = ~IC_LEFT;                                             |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| RRC                          | IC_LEFT() IC_RESULT()              | Rotate right with carry                                                                                                                    | IC_RESULT = (IC_LEFT << 1) | (IC_LEFT >> (sizeof(IC_LEFT)*8-1));  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| RLC                          | IC_LEFT() IC_RESULT()              | Rotate left with carry                                                                                                                     | IC_RESULT = (IC_LEFT << (sizeof(LC_LEFT)*8-1) ) | (IC_LEFT >> 1); |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| UNARYMINUS                   | IC_LEFT() IC_RESULT()              | Unary minus                                                                                                                                | IC_RESULT = - IC_LEFT;                                            |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| IPUSH                        | IC_LEFT()                          | Push the operand into stack                                                                                                                | NONE                                                              |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| IPOP                         | IC_LEFT()                          | Pop the operand from the stack                                                                                                             | NONE                                                              |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| CALL                         | IC_LEFT() IC_RESULT()              | Call the function represented by IC_LEFT                                                                                                   | IC_RESULT = IC_LEFT();                                            |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| PCALL                        | IC_LEFT() IC_RESULT()              | Call via function pointer                                                                                                                  | IC_RESULT = (*IC_LEFT)();                                         |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| RETURN                       | IC_LEFT()                          | Return the value in operand IC_LEFT                                                                                                        | return IC_LEFT;                                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| LABEL                        | IC_LABEL()                         | Label                                                                                                                                      | IC_LABEL:                                                         |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| GOTO                         | IC_LABEL()                         | Goto label                                                                                                                                 | goto IC_LABEL();                                                  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '+'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Addition                                                                                                                                   | IC_RESULT = IC_LEFT + IC_RIGHT                                    |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '-'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Subtraction                                                                                                                                | IC_RESULT = IC_LEFT - IC_RIGHT                                    |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '*'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Multiplication                                                                                                                             | IC_RESULT = IC_LEFT * IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '/'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Division                                                                                                                                   | IC_RESULT = IC_LEFT / IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '%'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Modulus                                                                                                                                    | IC_RESULT = IC_LEFT % IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '<'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Less than                                                                                                                                  | IC_RESULT = IC_LEFT < IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '>'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Greater than                                                                                                                               | IC_RESULT = IC_LEFT > IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| EQ_OP                        | IC_LEFT() IC_RIGHT() IC_RESULT()   | Equal to                                                                                                                                   | IC_RESULT = IC_LEFT == IC_RIGHT;                                  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| AND_OP                       | IC_LEFT() IC_RIGHT() IC_RESULT()   | Logical and operation                                                                                                                      | IC_RESULT = IC_LEFT && IC_RIGHT;                                  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| OR_OP                        | IC_LEFT() IC_RIGHT() IC_RESULT()   | Logical or operation                                                                                                                       | IC_RESULT = IC_LEFT || IC_RIGHT;                                  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '^'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Exclusive OR                                                                                                                               | IC_RESULT = IC_LEFT ^ IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '|'                          | IC_LEFT() IC_RIGHT() IC_RESULT()   | Bitwise OR                                                                                                                                 | IC_RESULT = IC_LEFT | IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| BITWISEAND                   | IC_LEFT() IC_RIGHT() IC_RESULT()   | Bitwise AND                                                                                                                                | IC_RESULT = IC_LEFT & IC_RIGHT;                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| LEFT_OP                      | IC_LEFT() IC_RIGHT() IC_RESULT()   | Left shift                                                                                                                                 | IC_RESULT = IC_LEFT << IC_RIGHT                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| RIGHT_OP                     | IC_LEFT() IC_RIGHT() IC_RESULT()   | Right shift                                                                                                                                | IC_RESULT = IC_LEFT >> IC_RIGHT                                   |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| GET_VALUE_
AT_ ADDRESS       | IC_LEFT() IC_RESULT()              | Indirect fetch                                                                                                                             | IC_RESULT = (*IC_LEFT);                                           |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| POINTER_SET                  | IC_RIGHT() IC_RESULT()             | Indirect set                                                                                                                               | (*IC_RESULT) = IC_RIGHT;                                          |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| '='                          | IC_RIGHT() IC_RESULT()             | Assignment                                                                                                                                 | IC_RESULT = IC_RIGHT;                                             |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| IFX                          | IC_COND IC_TRUE IC_LABEL           | Conditional jump. If true label is present then jump to true 
label if condition is true else jump to false label if condition 
is false   | if (IC_COND) goto IC_TRUE; 
  Or 
If (!IC_COND) goto IC_FALSE;    |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| ADDRESS_OF                   | IC_LEFT() IC_RESULT()              | Address of                                                                                                                                 | IC_RESULT = &IC_LEFT();                                           |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| JUMPTABLE                    | IC_JTCOND IC_JTLABELS              | Jump to list of labels depending on the value of JTCOND                                                                                    | Switch statement                                                  |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| CAST                         | IC_RIGHT() IC_LEFT() IC_RESULT()   | Cast types                                                                                                                                 | IC_RESULT = (typeof IC_LEFT) IC_RIGHT;                            |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| SEND                         | IC_LEFT()                          | This is used for passing parameters in registers; 
move IC_LEFT to the next available parameter register.                                  | None                                                              |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| RECV                         | IC_RESULT()                        | This is used for receiving parameters passed in registers;
Move the values in the next parameter register to IC_RESULT                     | None                                                              |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+
| (some more have been added)  |                                    |                                                                                                                                            | see f.e. gen51Code() in src/mcs51/gen.c                           |
+------------------------------+------------------------------------+--------------------------------------------------------------------------------------------------------------------------------------------+-------------------------------------------------------------------+




  ICode ExampleiCode

This section shows some details of iCode. The example C code does 
not do anything useful; it is used as an example to illustrate 
the intermediate code generated by the compiler.

1. __xdata int * p;
2. int gint;
3. /* This function does nothing useful. It is used
4.    for the purpose of explaining iCode */
5. short function (__data int *x)
6. {
7.   short i=10;   /* dead initialization eliminated */
8.   short sum=10; /* dead initialization eliminated */
9.   short mul;
10.  int j ;
11.  while (*x) *x++ = *p++;
12.    sum = 0 ;
13.  mul = 0;
14.  /* compiler detects i,j to be induction variables */
15.  for (i = 0, j = 10 ; i < 10 ; i++, j--) {
16.    sum += i;
17.    mul += i * 3;   /* this multiplication remains */
18.    gint += j * 3;  /* this multiplication changed to addition 
*/
19.  }
20.  return sum+mul;
21. }

In addition to the operands each iCode contains information about 
the filename and line it corresponds to in the source file. The 
first field in the listing should be interpreted as follows:
Filename(linenumber: iCode Execution sequence number : ICode hash 
table key : loop depth of the iCode).
Then follows the human readable form of the ICode operation. Each 
operand of this triplet form can be of three basic types a) 
compiler generated temporary b) user defined variable c) a 
constant value. Note that local variables and parameters are 
replaced by compiler generated temporaries. Live rangesLive range analysis
 are computed only for temporaries (i.e. live ranges are not 
computed for global variables). RegistersRegister allocation are 
allocated for temporaries only. Operands are formatted in the 
following manner:
Operand Name [lr live-from : live-to ] { type information } [ 
registers allocated ].
As mentioned earlier the live ranges are computed in terms of the 
execution sequence number of the iCodes, for example 
the iTemp0 is live from (i.e. first defined in iCode with 
execution sequence number 3, and is last used in the iCode with 
sequence number 5). For induction variables such as iTemp21 the 
live range computation extends the lifetime from the start to the 
end of the loop.
The register allocator used the live range information to 
allocate registers, the same registers may be used for different 
temporaries if their live ranges do not overlap, for example r0 
is allocated to both iTemp6 and to iTemp17 since their live 
ranges do not overlap. In addition the allocator also takes into 
consideration the type and usage of a temporary, for example 
itemp6 is a pointer to near space and is used as to fetch data 
from (i.e. used in GET_VALUE_AT_ADDRESS) so it is allocated a 
pointer register (r0). Some short lived temporaries are allocated 
to special registers which have meaning to the code generator 
e.g. iTemp13 is allocated to a pseudo register CC which tells the 
back end that the temporary is used only for a conditional jump 
the code generation makes use of this information to optimize a 
compare and jump ICode.
There are several loop optimizationsLoop optimization performed 
by the compiler. It can detect induction variables iTemp21(i) and 
iTemp23(j). Also note the compiler does selective strength 
reductionStrength reduction, i.e. the multiplication of an 
induction variable in line 18 (gint = j * 3) is changed to 
addition, a new temporary iTemp17 is allocated and assigned a 
initial value, a constant 3 is then added for each iteration of 
the loop. The compiler does not change the multiplicationMultiplication
 in line 17 however since the processor does support an 8 * 8 bit 
multiplication.
Note the dead code eliminationDead-code elimination optimization 
eliminated the dead assignments in line 7 & 8 to I and sum 
respectively.


Sample.c (5:1:0:0) _entry($9) :

Sample.c(5:2:1:0) proc _function [lr0:0]{function short}

Sample.c(11:3:2:0) iTemp0 [lr3:5]{_near * int}[r2] = recv 

Sample.c(11:4:53:0) preHeaderLbl0($11) :

Sample.c(11:5:55:0) iTemp6 [lr5:16]{_near * int}[r0] := iTemp0 
[lr3:5]{_near * int}[r2]

Sample.c(11:6:5:1) _whilecontinue_0($1) :

Sample.c(11:7:7:1) iTemp4 [lr7:8]{int}[r2 r3] = @[iTemp6 
[lr5:16]{_near * int}[r0]]

Sample.c(11:8:8:1) if iTemp4 [lr7:8]{int}[r2 r3] == 0 goto 
_whilebreak_0($3)

Sample.c(11:9:14:1) iTemp7 [lr9:13]{_far * int}[DPTR] := _p 
[lr0:0]{_far * int}

Sample.c(11:10:15:1) _p [lr0:0]{_far * int} = _p [lr0:0]{_far * 
int} + 0x2 {short}

Sample.c(11:13:18:1) iTemp10 [lr13:14]{int}[r2 r3] = @[iTemp7 
[lr9:13]{_far * int}[DPTR]]

Sample.c(11:14:19:1) *(iTemp6 [lr5:16]{_near * int}[r0]) := 
iTemp10 [lr13:14]{int}[r2 r3]

Sample.c(11:15:12:1) iTemp6 [lr5:16]{_near * int}[r0] = iTemp6 
[lr5:16]{_near * int}[r0] + 0x2 {short}

Sample.c(11:16:20:1) goto _whilecontinue_0($1)

Sample.c(11:17:21:0)_whilebreak_0($3) :

Sample.c(12:18:22:0) iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

Sample.c(13:19:23:0) iTemp11 [lr19:40]{short}[r3] := 0x0 {short}

Sample.c(15:20:54:0)preHeaderLbl1($13) :

Sample.c(15:21:56:0) iTemp21 [lr21:38]{short}[r4] := 0x0 {short}

Sample.c(15:22:57:0) iTemp23 [lr22:38]{int}[r5 r6] := 0xa {int}

Sample.c(15:23:58:0) iTemp17 [lr23:38]{int}[r7 r0] := 0x1e {int}

Sample.c(15:24:26:1)_forcond_0($4) :

Sample.c(15:25:27:1) iTemp13 [lr25:26]{char}[CC] = iTemp21 
[lr21:38]{short}[r4] < 0xa {short}

Sample.c(15:26:28:1) if iTemp13 [lr25:26]{char}[CC] == 0 goto 
_forbreak_0($7)

Sample.c(16:27:31:1) iTemp2 [lr18:40]{short}[r2] = iTemp2 
[lr18:40]{short}[r2] + ITemp21 [lr21:38]{short}[r4]

Sample.c(17:29:33:1) iTemp15 [lr29:30]{short}[r1] = iTemp21 
[lr21:38]{short}[r4] * 0x3 {short}

Sample.c(17:30:34:1) iTemp11 [lr19:40]{short}[r3] = iTemp11 
[lr19:40]{short}[r3] + iTemp15 [lr29:30]{short}[r1]

Sample.c(18:32:36:1:1) iTemp17 [lr23:38]{int}[r7 r0]= iTemp17 
[lr23:38]{int}[r7 r0]- 0x3 {short}

Sample.c(18:33:37:1) _gint [lr0:0]{int} = _gint [lr0:0]{int} + 
iTemp17 [lr23:38]{int}[r7 r0]

Sample.c(15:36:42:1) iTemp21 [lr21:38]{short}[r4] = iTemp21 
[lr21:38]{short}[r4] + 0x1 {short}

Sample.c(15:37:45:1) iTemp23 [lr22:38]{int}[r5 r6]= iTemp23 
[lr22:38]{int}[r5 r6]- 0x1 {short}

Sample.c(19:38:47:1) goto _forcond_0($4)

Sample.c(19:39:48:0)_forbreak_0($7) :

Sample.c(20:40:49:0) iTemp24 [lr40:41]{short}[DPTR] = iTemp2 
[lr18:40]{short}[r2] + ITemp11 [lr19:40]{short}[r3]

Sample.c(20:41:50:0) ret iTemp24 [lr40:41]{short}

Sample.c(20:42:51:0)_return($8) :

Sample.c(20:43:52:0) eproc _function [lr0:0]{ ia0 re0 
rm0}{function short}

Finally the code generated for this function:


.area DSEG (DATA)

_p::

  .ds 2

_gint::

  .ds 2

; sample.c 5

; ———————————————-

; function function

; ———————————————-

_function:

; iTemp0 [lr3:5]{_near * int}[r2] = recv 

  mov r2,dpl

; iTemp6 [lr5:16]{_near * int}[r0] := iTemp0 [lr3:5]{_near * 
int}[r2]

  mov ar0,r2

;_whilecontinue_0($1) :

00101$:

; iTemp4 [lr7:8]{int}[r2 r3] = @[iTemp6 [lr5:16]{_near * 
int}[r0]]

; if iTemp4 [lr7:8]{int}[r2 r3] == 0 goto _whilebreak_0($3)

  mov ar2,@r0

  inc r0

  mov ar3,@r0

  dec r0

  mov a,r2

  orl a,r3

  jz 00103$

00114$:

; iTemp7 [lr9:13]{_far * int}[DPTR] := _p [lr0:0]{_far * int}

  mov dpl,_p

  mov dph,(_p + 1)

; _p [lr0:0]{_far * int} = _p [lr0:0]{_far * int} + 0x2 {short}

  mov a,#0x02

  add a,_p

  mov _p,a

  clr a

  addc a,(_p + 1)

  mov (_p + 1),a

; iTemp10 [lr13:14]{int}[r2 r3] = @[iTemp7 [lr9:13]{_far * 
int}[DPTR]]

  movx a,@dptr

  mov r2,a

  inc dptr

  movx a,@dptr

  mov r3,a

; *(iTemp6 [lr5:16]{_near * int}[r0]) := iTemp10 
[lr13:14]{int}[r2 r3]

  mov @r0,ar2

  inc r0

  mov @r0,ar3

; iTemp6 [lr5:16]{_near * int}[r0] = 

; iTemp6 [lr5:16]{_near * int}[r0] + 

; 0x2 {short}

  inc r0

; goto _whilecontinue_0($1)

  sjmp 00101$

; _whilebreak_0($3) :

00103$:

; iTemp2 [lr18:40]{short}[r2] := 0x0 {short}

  mov r2,#0x00

; iTemp11 [lr19:40]{short}[r3] := 0x0 {short}

  mov r3,#0x00

; iTemp21 [lr21:38]{short}[r4] := 0x0 {short}

  mov r4,#0x00

; iTemp23 [lr22:38]{int}[r5 r6] := 0xa {int}

  mov r5,#0x0A

  mov r6,#0x00

; iTemp17 [lr23:38]{int}[r7 r0] := 0x1e {int}

  mov r7,#0x1E

  mov r0,#0x00

; _forcond_0($4) :

00104$:

; iTemp13 [lr25:26]{char}[CC] = iTemp21 [lr21:38]{short}[r4] < 
0xa {short}

; if iTemp13 [lr25:26]{char}[CC] == 0 goto _forbreak_0($7)

  clr c

  mov a,r4

  xrl a,#0x80

  subb a,#0x8a

  jnc 00107$

00115$:

; iTemp2 [lr18:40]{short}[r2] = iTemp2 [lr18:40]{short}[r2] + 

; iTemp21 [lr21:38]{short}[r4]

  mov a,r4

  add a,r2

  mov r2,a

; iTemp15 [lr29:30]{short}[r1] = iTemp21 [lr21:38]{short}[r4] * 
0x3 {short}

  mov b,#0x03

  mov a,r4

  mul ab

  mov r1,a

; iTemp11 [lr19:40]{short}[r3] = iTemp11 [lr19:40]{short}[r3] + 

; iTemp15 [lr29:30]{short}[r1]

  add a,r3

  mov r3,a

; iTemp17 [lr23:38]{int}[r7 r0]= iTemp17 [lr23:38]{int}[r7 r0]- 
0x3 {short}

  mov a,r7

  add a,#0xfd

  mov r7,a

  mov a,r0

  addc a,#0xff

  mov r0,a

; _gint [lr0:0]{int} = _gint [lr0:0]{int} + iTemp17 
[lr23:38]{int}[r7 r0]

  mov a,r7

  add a,_gint

  mov _gint,a

  mov a,r0

  addc a,(_gint + 1)

  mov (_gint + 1),a

; iTemp21 [lr21:38]{short}[r4] = iTemp21 [lr21:38]{short}[r4] + 
0x1 {short}

  inc r4

; iTemp23 [lr22:38]{int}[r5 r6]= iTemp23 [lr22:38]{int}[r5 r6]- 
0x1 {short}

  dec r5

  cjne r5,#0xff,00104$

  dec r6

; goto _forcond_0($4)

  sjmp 00104$

; _forbreak_0($7) :

00107$:

; ret iTemp24 [lr40:41]{short}

  mov a,r3

  add a,r2

  mov dpl,a

; _return($8) :

00108$:

  ret


9.2 A few words about basic block successors, predecessors and 
  dominators

Successors are basic blocksBasic blocks that might execute after 
this basic block.
Predecessors are basic blocks that might execute before reaching 
this basic block.
Dominators are basic blocks that WILL execute before reaching 
this basic block.


[basic block 1]

if (something)

    [basic block 2]

else

    [basic block 3]

[basic block 4]


a) succList of [BB2] = [BB4], of [BB3] = [BB4], of [BB1] = 
[BB2,BB3]

b) predList of [BB2] = [BB1], of [BB3] = [BB1], of [BB4] = 
[BB2,BB3]

c) domVect of [BB4] = BB1 ... here we are not sure if BB2 or BB3 
was executed but we are SURE that BB1 was executed.

Acknowledgments

http://sdcc.sourceforge.net/#Who

Thanks to all the other volunteer developers who have helped with 
coding, testing, web-page creation, distribution sets, etc. You 
know who you are :-)

Thanks to Sourceforge http://sourceforge.net/ which has hosted 
the project since 1999 and donates significant download 
bandwidth.

Also thanks to all SDCC Distributed Compile Farm members for 
donating CPU cycles and bandwidth for snapshot builds.


This document was initially written by Sandeep Dutta and updated 
by SDCC developers.

All product names mentioned herein may be trademarksTrademarks of 
their respective companies. 

  Alphabetical index

To avoid confusion, the installation and building options for 
SDCC itself (chapter 2) are not part of the index.

[LaTeX Command: printindex]

