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403 lines
12 KiB
Plaintext
<!doctype linuxdoc system>
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<article>
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<title>Commodore 64 specific information for cc65
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<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
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<date>2003-09-23
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<abstract>
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An overview over the C64 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 C64 runtime system as it comes with the
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cc65 C compiler. It describes the memory layout, C64 specific header files,
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available drivers, and any pitfalls specific to that platform.
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Please note that C64 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 C64 target
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is a machine language program with a one line BASIC stub, which calls the
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machine language part via SYS. This means that a program can be loaded as
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BASIC program and started with RUN. It is of course possible to change this
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behaviour by using a modified startup file and linker config.
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<sect>Memory layout<p>
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cc65 generated programs with the default setup run with the I/O area and the
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kernal ROM enabled (memory under the kernal may be used for graphics or as
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extended memory - see the sections about graphics and extended memory
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drivers). The BASIC ROM is disabled, which gives a usable memory range of
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$0800 - $CFFF. This means that kernal entry points may be called
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directly, but using the BASIC ROM is not possible without additional code.
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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 is located at $400 (as in the standard setup).
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<tag/Stack/
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The C runtime stack is located at $CFFF and growing downwards.
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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>Linker configurations<p>
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The ld65 linker comes with a builtin config file for the Commodore 64,
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which is used via <tt/-t c64/ (and displayed via <tt/--dump-config c64/). The
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c64 package comes with additional secondary linker config files, which are
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used via <tt/-C <configfile>/.
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<sect1>builtin config file<p>
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The builtin configuration is tailored to C programs. It supplies the load
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address and a small BASIC stub that starts the compiled program using a SYS
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command.
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<sect1><tt/c64-asm.cfg/<p>
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This configuration is made for assembler programmers who don't need a special
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setup. The default start address is $801. It can be changed with the
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linker command line option <tt/--start-addr/. All standard segments with the
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exception of <tt/zeropage/ are written to the output file and a two byte load
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address is prepended.
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To use this config file, assemble with <tt/-t c64/ and link with <tt/-C
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c64-asm.cfg/. The former will make sure that correct character translation is
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in effect, while the latter supplies the actual config. When using <tt/cl65/,
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use both command line options.
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Sample command line for <tt/cl65/:
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<tscreen><verb>
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cl65 -o file.prg -t c64 -C c64-asm.cfg source.s
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</verb></tscreen>
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To generate code that loads to $C000:
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<tscreen><verb>
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cl65 -o file.prg --start-addr $C000 -t c64 -C c64-asm.cfg source.s
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</verb></tscreen>
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It is also possible to add a small BASIC header to the program, that uses SYS
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to jump to the program entry point (which is the start of the code segment).
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The advantage is that the program can be started using RUN.
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To generate a program with a BASIC SYS header, use
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<tscreen><verb>
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cl65 -o file.prg -u __EXEHDR__ -t c64 -C c64-asm.cfg source.s
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</verb></tscreen>
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Please note that in this case a changed start address doesn't make sense,
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since the program must be loaded to the BASIC start address.
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<sect>Platform specific header files<p>
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Programs containing C64 specific code may use the <tt/c64.h/ or <tt/cbm.h/
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header files. Using the later may be an option when writing code for more than
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one CBM platform, since it includes <tt/c64.h/ and declares several functions
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common to all CBM platforms.
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<sect1>C64 specific functions<p>
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The functions listed below are special for the C64. 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>get_ostype
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</itemize>
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<sect1>CBM specific functions<p>
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Some functions are available for all (or at least most) of the Commodore
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machines. See the <htmlurl url="funcref.html" name="function reference"> for
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declaration and usage.
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<itemize>
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<item>cbm_close
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<item>cbm_closedir
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<item>cbm_k_setlfs
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<item>cbm_k_setnam
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<item>cbm_k_load
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<item>cbm_k_save
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<item>cbm_k_open
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<item>cbm_k_close
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<item>cbm_k_readst
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<item>cbm_k_chkin
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<item>cbm_k_ckout
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<item>cbm_k_basin
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<item>cbm_k_bsout
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<item>cbm_k_clrch
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<item>cbm_load
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<item>cbm_open
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<item>cbm_opendir
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<item>cbm_read
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<item>cbm_readdir
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<item>cbm_save
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<item>cbm_write
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<item>get_tv
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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/c64.h/ header file do allow
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access to hardware located in the address space. Some variables are
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structures, accessing the struct fields will access the chip registers.
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<descrip>
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<tag><tt/VIC/</tag>
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The <tt/VIC/ structure allows access to the VIC II (the graphics
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controller). See the <tt/_vic2.h/ header file located in the include
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directory for the declaration of the structure.
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<tag><tt/SID/</tag>
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The <tt/SID/ structure allows access to the SID (the sound interface
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device). See the <tt/_sid.h/ header file located in the include directory
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for the declaration of the structure.
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<tag><tt/CIA1, CIA2/</tag>
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Access to the two CIA (complex interface adapter) chips is available via
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the <tt/CIA1/ and <tt/CIA2/ variables. The structure behind these variables
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is explained in <tt/_6526.h/.
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<tag><tt/COLOR_RAM/</tag>
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A character array that mirrors the color RAM of the C64 at $D800.
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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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<em>Note:</em> All available graphics drivers for the TGI interface will use
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the space below the I/O area and kernal ROM, so you can have hires graphics in
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the standard setup without any memory loss or need for a changed
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configuration.
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<descrip>
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<tag><tt/c64-hi.tgi/</tag>
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This driver features a resolution of 320*200 with two colors and an
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adjustable palette (that means that the two colors can be chosen out of a
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palette of the 16 C64 colors).
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</descrip><p>
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<sect1>Extended memory drivers<p>
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<descrip>
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<tag><tt/c64-c256k.emd/</tag>
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A driver for the C64 256K memory expansion. This driver offers 768 pages of
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256 bytes each. Written and contributed by Marco van den Heuvel.
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<tag><tt/c64-dqbb.emd/</tag>
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A driver for the Double Quick Brown Box cartridge. This driver offers
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64 pages of 256 bytes each. Written and contributed by Marco van den Heuvel.
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<tag><tt/c64-georam.emd/</tag>
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A driver for the Berkeley Softworks GeoRam cartridge. The driver will
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determine the available RAM from the connected cartridge. It supports 64KB
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up to 2048KB of RAM.
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<tag><tt/c64-isepic.emd/</tag>
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A driver for the ISEPIC cartridge. This driver offers just 8 pages of 256
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bytes each. Written and contributed by Marco van den Heuvel.
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<tag><tt/c64-ram.emd/</tag>
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A driver for the hidden RAM below the I/O area and kernal ROM. Supports 48
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256 byte pages. Please note that this driver is incompatible with any of the
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graphics drivers!
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<tag><tt/c64-ramcart.emd/</tag>
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A driver for the RamCart 64/128 written and contributed by Maciej Witkowiak.
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Will test the hardware for the available RAM.
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<tag><tt/c64-reu.emd/</tag>
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A driver for the CBM REUs. The driver will determine from the connected REU
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if it supports 128KB of RAM or more. In the latter case, 256KB are assumed,
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but since there are no range checks, the application can use more memory if
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it has better knowledge about the hardware than the driver.
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<tag><tt/c64-vdc.emd/</tag>
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A driver for the VDC memory of the C128. Written and contributed by Maciej
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Witkowiak. Can be used if the program is running in C64 mode of the C128.
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Autodetects the amount of memory available (16 or 64K) and offers 64 or 256
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pages of 256 bytes each.
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<tag><tt/dtv-himem.emd/</tag>
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A driver for the C64 D2TV (the second or PAL version). This driver offers
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indeed 7680 pages of 256 bytes each.
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</descrip><p>
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<sect1>Joystick drivers<p>
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<descrip>
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<tag><tt/c64-hitjoy.joy/</tag>
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Driver for the Digital Excess & Hitmen adapter contributed by Groepaz. See
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<htmlurl url="http://www.digitalexcess.de/downloads/productions.php"
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name="http://www.digitalexcess.de/downloads/productions.php"> on
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instructions how to build one. Up to four joysticks are supported.
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<tag><tt/c64-ptvjoy.joy/</tag>
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Driver for the Protovision 4-player adapter contributed by Groepaz. See
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<htmlurl url="http://www.protovision-online.de/hardw/hardwstart.htm"
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name="http://www.protovision-online.de/hardw/hardwstart.htm"> for prices and
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building instructions. Up to four joysticks are supported.
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<tag><tt/c64-stdjoy.joy/</tag>
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Supports up to two standard joysticks connected to the joysticks port of
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the C64.
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<tag><tt/c64-numpad.joy/</tag>
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Supports one joystick emulated by the numberpad of the C128 in C64 mode,
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the firebutton is labeled &dquot;5&dquot; and ENTER.
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</descrip><p>
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<sect1>Mouse drivers<p>
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<descrip>
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<tag><tt/c64-1351.mou/</tag>
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Supports a standard mouse connected to port #0 of the C64.
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<tag><tt/c64-joy.mou/</tag>
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Supports a mouse emulated by a standard joystick e.g. 1350 mouse in port
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#1 of the C64.
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<tag><tt/c64-pot.mou/</tag>
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Supports a potentiometer device e.g. Koala Pad connected to port #1 of
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the C64.
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</descrip><p>
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<sect1>RS232 device drivers<p>
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<descrip>
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<tag><tt/c64-swlink.ser/</tag>
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Driver for the SwiftLink cartridge. Supports up to 38400 baud, hardware flow
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control (RTS/CTS) and interrupt driven receives. Note that because of the
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peculiarities of the 6551 chip together with the use of the NMI, transmits
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are not interrupt driven, and the transceiver blocks if the receiver asserts
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flow control because of a full buffer.
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</descrip><p>
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<sect>Limitations<p>
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<sect>Other hints<p>
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<sect1>Escape code<p>
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For an Esc press CTRL and [ key.
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<sect1>Passing arguments to the program<p>
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Command line arguments can be passed to <tt/main()/. Since this is not
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supported by BASIC, the following syntax was chosen:
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<tscreen><verb>
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RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
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</verb></tscreen>
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<enum>
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<item>Arguments are separated by spaces.
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<item>Arguments may be quoted.
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<item>Leading and trailing spaces around an argument are ignored. Spaces within
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a quoted argument are allowed.
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<item>The first argument passed to <tt/main/ is the program name.
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<item>A maximum number of 10 arguments (including the program name) are
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supported.
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</enum>
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<sect1>Program return code<p>
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The program return code (low byte) is passed back to BASIC by use of the
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<tt/ST/ variable.
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<sect1>Interrupts<p>
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The runtime for the C64 uses routines marked as <tt/.INTERRUPTOR/ for
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interrupt handlers. Such routines must be written as simple machine language
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subroutines and will be called automatically by the interrupt handler code
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when they are linked into a program. See the discussion of the <tt/.CONDES/
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feature in the <htmlurl url="ca65.html" name="assembler manual">.
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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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