1 <!doctype linuxdoc system>
5 <title>Commodore 64 specific information for cc65
6 <author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
10 An overview over the C64 runtime system as it is implemented for the cc65 C
14 <!-- Table of contents -->
17 <!-- Begin the document -->
21 This file contains an overview of the C64 runtime system as it comes with the
22 cc65 C compiler. It describes the memory layout, C64 specific header files,
23 available drivers, and any pitfalls specific to that platform.
25 Please note that C64 specific functions are just mentioned here, they are
26 described in detail in the separate <htmlurl url="funcref.html" name="function
27 reference">. Even functions marked as "platform dependent" may be available on
28 more than one platform. Please see the function reference for more
32 <sect>Binary format<p>
34 The standard binary output format generated by the linker for the C64 target
35 is a machine language program with a one line BASIC stub, which calls the
36 machine language part via SYS. This means that a program can be loaded as
37 BASIC program and started with RUN. It is of course possible to change this
38 behaviour by using a modified startup file and linker config.
41 <sect>Memory layout<p>
43 cc65 generated programs with the default setup run with the I/O area and the
44 kernal ROM enabled (memory under the kernal may be used for graphics or as
45 extended memory - see the sections about graphics and extended memory
46 drivers). The BASIC ROM is disabled, which gives a usable memory range of
47 $0800 - $CFFF. This means that kernal entry points may be called
48 directly, but using the BASIC ROM is not possible without additional code.
54 The text screen is located at $400 (as in the standard setup).
57 The C runtime stack is located at $CFFF and growing downwards.
60 The C heap is located at the end of the program and grows towards the C
66 <sect>Linker configurations<p>
68 The ld65 linker comes with a builtin config file for the Commodore 64,
69 which is used via <tt/-t c64/ (and displayed via <tt/--dump-config c64/). The
70 c64 package comes with additional secondary linker config files, which are
71 used via <tt/-C <configfile>/.
74 <sect1>builtin config file<p>
76 The builtin configuration is tailored to C programs. It supplies the load
77 address and a small BASIC stub that starts the compiled program using a SYS
81 <sect1><tt/c64-asm.cfg/<p>
83 This configuration is made for assembler programmers who don't need a special
84 setup. The default start address is $801. It can be changed with the
85 linker command line option <tt/--start-addr/. All standard segments with the
86 exception of <tt/zeropage/ are written to the output file and a two byte load
89 To use this config file, assemble with <tt/-t c64/ and link with <tt/-C
90 c64-asm.cfg/. The former will make sure that correct character translation is
91 in effect, while the latter supplies the actual config. When using <tt/cl65/,
92 use both command line options.
94 Sample command line for <tt/cl65/:
97 cl65 -o file.prg -t c64 -C c64-asm.cfg source.s
100 To generate code that loads to $C000:
103 cl65 -o file.prg --start-addr $C000 -t c64 -C c64-asm.cfg source.s
106 It is also possible to add a small BASIC header to the program, that uses SYS
107 to jump to the program entry point (which is the start of the code segment).
108 The advantage is that the program can be started using RUN.
110 To generate a program with a BASIC SYS header, use
113 cl65 -o file.prg -u __EXEHDR__ -t c64 -C c64-asm.cfg source.s
116 Please note that in this case a changed start address doesn't make sense,
117 since the program must be loaded to the BASIC start address.
120 <sect>Platform specific header files<p>
122 Programs containing C64 specific code may use the <tt/c64.h/ or <tt/cbm.h/
123 header files. Using the later may be an option when writing code for more than
124 one CBM platform, since it includes <tt/c64.h/ and declares several functions
125 common to all CBM platforms.
128 <sect1>C64 specific functions<p>
130 The functions listed below are special for the C64. See the <htmlurl
131 url="funcref.html" name="function reference"> for declaration and usage.
138 <sect1>CBM specific functions<p>
140 Some functions are available for all (or at least most) of the Commodore
141 machines. See the <htmlurl url="funcref.html" name="function reference"> for
142 declaration and usage.
170 <sect1>Hardware access<p>
172 The following pseudo variables declared in the <tt/c64.h/ header file do allow
173 access to hardware located in the address space. Some variables are
174 structures, accessing the struct fields will access the chip registers.
179 The <tt/VIC/ structure allows access to the VIC II (the graphics
180 controller). See the <tt/_vic2.h/ header file located in the include
181 directory for the declaration of the structure.
184 The <tt/SID/ structure allows access to the SID (the sound interface
185 device). See the <tt/_sid.h/ header file located in the include directory
186 for the declaration of the structure.
188 <tag><tt/CIA1, CIA2/</tag>
189 Access to the two CIA (complex interface adapter) chips is available via
190 the <tt/CIA1/ and <tt/CIA2/ variables. The structure behind these variables
191 is explained in <tt/_6526.h/.
193 <tag><tt/COLOR_RAM/</tag>
194 A character array that mirrors the color RAM of the C64 at $D800.
200 <sect>Loadable drivers<p>
202 <sect1>Graphics drivers<p>
204 <em>Note:</em> All available graphics drivers for the TGI interface will use
205 the space below the I/O area and kernal ROM, so you can have hires graphics in
206 the standard setup without any memory loss or need for a changed
210 <tag><tt/c64-hi.tgi/</tag>
211 This driver features a resolution of 320*200 with two colors and an
212 adjustable palette (that means that the two colors can be chosen out of a
213 palette of the 16 C64 colors).
217 <sect1>Extended memory drivers<p>
221 <tag><tt/c64-c256k.emd/</tag>
222 A driver for the C64 256K memory expansion. This driver offers 768 pages of
223 256 bytes each. Written and contributed by Marco van den Heuvel.
225 <tag><tt/c64-dqbb.emd/</tag>
226 A driver for the Double Quick Brown Box cartridge. This driver offers
227 64 pages of 256 bytes each. Written and contributed by Marco van den Heuvel.
229 <tag><tt/c64-georam.emd/</tag>
230 A driver for the Berkeley Softworks GeoRam cartridge. The driver will
231 determine the available RAM from the connected cartridge. It supports 64KB
234 <tag><tt/c64-isepic.emd/</tag>
235 A driver for the ISEPIC cartridge. This driver offers just 8 pages of 256
236 bytes each. Written and contributed by Marco van den Heuvel.
238 <tag><tt/c64-ram.emd/</tag>
239 A driver for the hidden RAM below the I/O area and kernal ROM. Supports 48
240 256 byte pages. Please note that this driver is incompatible with any of the
243 <tag><tt/c64-ramcart.emd/</tag>
244 A driver for the RamCart 64/128 written and contributed by Maciej Witkowiak.
245 Will test the hardware for the available RAM.
247 <tag><tt/c64-reu.emd/</tag>
248 A driver for the CBM REUs. The driver will determine from the connected REU
249 if it supports 128KB of RAM or more. In the latter case, 256KB are assumed,
250 but since there are no range checks, the application can use more memory if
251 it has better knowledge about the hardware than the driver.
253 <tag><tt/c64-vdc.emd/</tag>
254 A driver for the VDC memory of the C128. Written and contributed by Maciej
255 Witkowiak. Can be used if the program is running in C64 mode of the C128.
256 Autodetects the amount of memory available (16 or 64K) and offers 64 or 256
257 pages of 256 bytes each.
259 <tag><tt/dtv-himem.emd/</tag>
260 A driver for the C64 D2TV (the second or PAL version). This driver offers
261 indeed 7680 pages of 256 bytes each.
266 <sect1>Joystick drivers<p>
270 <tag><tt/c64-hitjoy.joy/</tag>
271 Driver for the Digital Excess & Hitmen adapter contributed by Groepaz. See
272 <htmlurl url="http://www.digitalexcess.de/downloads/productions.php"
273 name="http://www.digitalexcess.de/downloads/productions.php"> on
274 instructions how to build one. Up to four joysticks are supported.
276 <tag><tt/c64-ptvjoy.joy/</tag>
277 Driver for the Protovision 4-player adapter contributed by Groepaz. See
278 <htmlurl url="http://www.protovision-online.de/hardw/hardwstart.htm"
279 name="http://www.protovision-online.de/hardw/hardwstart.htm"> for prices and
280 building instructions. Up to four joysticks are supported.
282 <tag><tt/c64-stdjoy.joy/</tag>
283 Supports up to two standard joysticks connected to the joysticks port of
286 <tag><tt/c64-numpad.joy/</tag>
287 Supports one joystick emulated by the numberpad of the C128 in C64 mode,
288 the firebutton is labeled &dquot;5&dquot; and ENTER.
293 <sect1>Mouse drivers<p>
297 <tag><tt/c64-1351.mou/</tag>
298 Supports a standard mouse connected to port #0 of the C64.
300 <tag><tt/c64-joy.mou/</tag>
301 Supports a mouse emulated by a standard joystick e.g. 1350 mouse in port
304 <tag><tt/c64-pot.mou/</tag>
305 Supports a potentiometer device e.g. Koala Pad connected to port #1 of
311 <sect1>RS232 device drivers<p>
315 <tag><tt/c64-swlink.ser/</tag>
316 Driver for the SwiftLink cartridge. Supports up to 38400 baud, hardware flow
317 control (RTS/CTS) and interrupt driven receives. Note that because of the
318 peculiarities of the 6551 chip together with the use of the NMI, transmits
319 are not interrupt driven, and the transceiver blocks if the receiver asserts
320 flow control because of a full buffer.
332 <sect1>Passing arguments to the program<p>
334 Command line arguments can be passed to <tt/main()/. Since this is not
335 supported by BASIC, the following syntax was chosen:
338 RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
342 <item>Arguments are separated by spaces.
343 <item>Arguments may be quoted.
344 <item>Leading and trailing spaces around an argument are ignored. Spaces within
345 a quoted argument are allowed.
346 <item>The first argument passed to <tt/main/ is the program name.
347 <item>A maximum number of 10 arguments (including the program name) are
352 <sect1>Program return code<p>
354 The program return code (low byte) is passed back to BASIC by use of the
360 The runtime for the C64 uses routines marked as <tt/.INTERRUPTOR/ for
361 interrupt handlers. Such routines must be written as simple machine language
362 subroutines and will be called automatically by the interrupt handler code
363 when they are linked into a program. See the discussion of the <tt/.CONDES/
364 feature in the <htmlurl url="ca65.html" name="assembler manual">.
368 <sect>Bugs/Feedback<p>
370 If you have problems using the library, if you find any bugs, or if you're
371 doing something interesting with it, I would be glad to hear from you. Feel
372 free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
373 name="uz@cc65.org">).
379 This software is provided 'as-is', without any expressed or implied
380 warranty. In no event will the authors be held liable for any damages
381 arising from the use of this software.
383 Permission is granted to anyone to use this software for any purpose,
384 including commercial applications, and to alter it and redistribute it
385 freely, subject to the following restrictions:
388 <item> The origin of this software must not be misrepresented; you must not
389 claim that you wrote the original software. If you use this software
390 in a product, an acknowledgment in the product documentation would be
391 appreciated but is not required.
392 <item> Altered source versions must be plainly marked as such, and must not
393 be misrepresented as being the original software.
394 <item> This notice may not be removed or altered from any source