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215 lines
6.5 KiB
Plaintext
215 lines
6.5 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Atari specific information for cc65
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<author>Shawn Jefferson, <htmlurl url="mailto:shawnjefferson@24fightingchickens.com" name="shawnjefferson@24fightingchickens.com">
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Christian Groessler, <htmlurl url="mailto:cpg@aladdin.de" name="cpg@aladdin.de">
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<date>16-Oct-2003
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<abstract>
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An overview over the Atari runtime system as it is implemented for the cc65 C
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compiler.
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</abstract>
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<!-- Table of contents -->
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<toc>
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<!-- Begin the document -->
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<sect>Overview<p>
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This file contains an overview of the Atari runtime system as it comes
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with the cc65 C compiler. It describes the memory layout, Atari specific
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header files, available drivers, and any pitfalls specific to that
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platform.
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Please note that Atari specific functions are just mentioned here, they are
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described in detail in the separate <htmlurl url="funcref.html" name="function
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reference">. Even functions marked as "platform dependent" may be available on
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more than one platform. Please see the function reference for more
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information.
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<sect>Binary format<p>
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The standard binary output format generated by the linker for the
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Atari target is a machine language program with a standard executable
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header (FF FF <start address> <end address>). These values are
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calculated in the crt0.s file from the __CODE_LOAD__ and __BSS_LOAD__
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values, so keep this in mind if you create a custom linker config file
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and start moving segments around. You can override this behaviour by
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creating your own crt0.s file and linking it into your program. A run
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vector is added to the end of the file ($02E0 <run vector>)
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and is calculated using __CODE_LOAD__ in crt0.s also.
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<sect>Memory layout<p>
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The default linker script assumes that the BASIC ROM is disabled (or
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the BASIC cartridge unplugged). This gives a usable memory range from
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$2E00 - $BC1F. The library startup code examines the
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current memory configuration, which depends on the size of the
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installed memory and cartridges present, by inspecting the value in
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the MEMTOP ($2E5) variable. Then the initial stack pointer,
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which indicates the upper bound of memory used, is adjusted. The load
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address of $2E00 was chosen to accommodate having a DOS loaded
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and a driver that resides in low memory such as the 850 R: handler.
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You can override this behaviour by creating a custom linker config
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file.
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Special locations:
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<descrip>
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<tag/Text screen/
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The text screen depends on the installed memory size and cartridges
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and can be obtained from the SAVMSC variable ($58).
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<tag/Stack/
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The C runtime stack is located at MEMTOP and grows downwards,
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regardless of how your linker config file is setup. This
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accomodates the different memory configurations of the Atari
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machines, as well as having a cartridge installed. You can override
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this behaviour by writing your own crt0.s file and linking it to
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your program.
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<tag/Heap/
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The C heap is located at the end of the program and grows towards the C
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runtime stack.
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</descrip><p>
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<sect>Platform specific header files<p>
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Programs containing Atari specific code may use the <tt/atari.h/
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header file.
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<sect1>Atari specific functions<p>
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The functions listed below are special for the Atari. See the <htmlurl
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url="funcref.html" name="function reference"> for declaration and usage.
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<itemize>
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<item>_gtia_mkcolor
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<item>get_ostype
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<item>get_tv
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<item>getcolor
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<item>getdefdev
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<item>graphics
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<item>rest_vecs
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<item>save_vecs
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<item>scroll
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<item>setcolor
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<item>setcolor_low
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</itemize>
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<sect1>Hardware access<p>
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The following pseudo variables declared in the <tt/atari.h/ header
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file do allow access to hardware located in the address space. Some
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variables are structures, accessing the struct fields will access the
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chip registers.
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<descrip>
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<tag><tt/GTIA_READ/ and <tt/GTIA_WRITE/</tag>
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The <tt/GTIA_READ/ structure allows read access to the GTIA. The
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<tt/GTIA_WRITE/ structure allows write access to the GTIA.
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See the <tt/_gtia.h/ header file located in the include directory
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for the declaration of the structure.
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<tag><tt/POKEY_READ/ and <tt/POKEY_WRITE/</tag>
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The <tt/POKEY_READ/ structure allows read access to the POKEY. The
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<tt/POKEY_WRITE/ structure allows write access to the POKEY.
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See the <tt/_pokey.h/ header file located in the include directory
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for the declaration of the structure.
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<tag><tt/ANTIC/</tag>
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The <tt/ANTIC/ structure allows read access to the ANTIC.
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See the <tt/_antic.h/ header file located in the include directory
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for the declaration of the structure.
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<tag><tt/PIA/</tag>
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The <tt/PIA/ structure allows read access to the PIA 6520.
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See the <tt/_pia.h/ header file located in the include directory
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for the declaration of the structure.
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</descrip><p>
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<sect>Loadable drivers<p>
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<sect1>Graphics drivers<p>
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Currently there are no graphics drivers available for the Atari platform.
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<sect1>Extended memory drivers<p>
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Currently there are no extended memory drivers available for the Atari
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platform.
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/atari-stdjoy.joy/</tag>
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Supports up to four standard joysticks connected to the joystick ports of
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the Atari.
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</descrip><p>
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<sect1>Mouse drivers<p>
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Currently no drivers available (in fact, the API for loadable mouse drivers
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does not exist). There is a static driver you can use.
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<sect1>RS232 device drivers<p>
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Currently there are no RS232 loadable drivers available for the Atari
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platform. There is a static driver you can use.
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<sect>Other hints<p>
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<sect>Bugs/Feedback<p>
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If you have problems using the library, if you find any bugs, or if you're
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doing something interesting with it, I would be glad to hear from you. Feel
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free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
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name="uz@cc65.org">).
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<sect>License<p>
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This software is provided 'as-is', without any expressed or implied
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warranty. In no event will the authors be held liable for any damages
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arising from the use of this software.
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Permission is granted to anyone to use this software for any purpose,
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including commercial applications, and to alter it and redistribute it
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freely, subject to the following restrictions:
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<enum>
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<item> The origin of this software must not be misrepresented; you must not
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claim that you wrote the original software. If you use this software
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in a product, an acknowledgment in the product documentation would be
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appreciated but is not required.
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<item> Altered source versions must be plainly marked as such, and must not
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be misrepresented as being the original software.
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<item> This notice may not be removed or altered from any source
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distribution.
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</enum>
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</article>
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