Atari 2600 specific information for cc65 <author> <url url="mailto:contact@florentflament.com" name="Florent Flament"><newline> <abstract> An overview over the Atari 2600 runtime system as it is implemented for the cc65 C compiler. </abstract>  <toc>  <sect>Overview 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. <sect>Binary format The default binary output format generated by the linker for the Atari 2600 target is a 4K cartridge image. <sect>Memory layout 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: <descrip> <tag/Stack/ The C runtime stack is located at $00FF - __STACKSIZE__ and growing downwards. <tag/Heap/ The C heap is located at $0080 and grows upwards. </descrip> <sect>Start-up condition 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. <sect>Platform specific header files Programs containing Atari 2600 specific code may use the <tt/atari2600.h/ header file. The following pseudo variables declared in the <tt/atari2600.h/ header file allow access to the Atari 2600 TIA & RIOT chips registers. <descrip> <tag><tt/TIA/</tag> The <tt/TIA/ structure allows read/write access to the Atari 2600 TIA chip registers. See the <tt/_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. <tag><tt/RIOT/</tag> The <tt/RIOT/ structure allows read/write access to the Atari 2600 RIOT chip registers. See the <tt/_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. </descrip> <sect>Loadable drivers There are no drivers for the Atari 2600. <sect>Limitations TBD <sect>Other hints One may write a custom linker configuration file to tune the memory layout of a program. See the <tt/atari2600.cfg/ file in the cfg directory as a starting point. <sect>License 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: <enum> <item> The origin of this software must not be misrepresented; you must not claim that you wrote the original software. If you use this software in a product, an acknowledgment in the product documentation would be appreciated but is not required. <item> Altered source versions must be plainly marked as such, and must not be misrepresented as being the original software. <item> This notice may not be removed or altered from any source distribution. </enum> </article>