This file contains an overview of the Atari 2600 runtime system as it comes with the cc65 C compiler. It describes the memory layout, Atari 2600 specific header files and any pitfalls specific to that platform.
The default binary output format generated by the linker for the Atari 2600 target is a 4K cartridge image.
cc65 generated programs with the default setup can use RAM from $0080 to $00FF - __STACKSIZE__, where __STACKSIZE__ is the size of the system stack with a default value of 16 bytes. The size of the system stack can be customized by defining the __STACKSIZE__ linker variable.
Special locations:
The C runtime stack is located at $00FF - __STACKSIZE__ and growing downwards.
The C heap is located at $0080 and grows upwards.
When powered-up, the Atari 2600 TIA registers contain random values. During the initialization phase, the start-up code needs to initialize the TIA registers to sound values (or else the console has an unpredictable behavior). In this implementation, zeros are written to all of TIA registers during the start-up phase.
Note that RIOT registers (mostly timers) are left uninitialized, as they don't have any consequence on the console behavior.
Programs containing Atari 2600 specific code may use the
atari2600.h header file.
The following pseudo variables declared in the atari2600.h header
file allow access to the Atari 2600 TIA & RIOT chips registers.
TIAThe TIA structure allows read/write access
to the Atari 2600 TIA chip registers. See the _tia.h header
file located in the include directory for the declaration of the
structure. Also refer to the Stella Programmer's Guide by Steve
Wright for a detailed description of the chip and its registers.
RIOTThe RIOT structure allows read/write
access to the Atari 2600 RIOT chip registers. See the
_riot.h header file located in the include directory for the
declaration of the structure. Also refer to the Stella Programmer's
Guide by Steve Wright for a detailed description of the chip and its
registers.
There are no drivers for the Atari 2600.
TBD
One may write a custom linker configuration file to tune the memory
layout of a program. See the atari2600.cfg file in the cfg
directory as a starting point.
This software is provided 'as-is', without any expressed or implied warranty. In no event will the authors be held liable for any damages arising from the use of this software.
Permission is granted to anyone to use this software for any purpose, including commercial applications, and to alter it and redistribute it freely, subject to the following restrictions: