1 <!doctype linuxdoc system>
5 <title>Commodore VIC20 (aka VC20) specific information for cc65
6 <author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
7 Stefan A. Haubenthal, <htmlurl url="mailto:polluks@sdf.lonestar.org" name="polluks@sdf.lonestar.org">
11 An overview over the VIC20 runtime system as it is implemented for the cc65 C
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18 <!-- Begin the document -->
22 This file contains an overview of the VIC20 runtime system as it comes with the
23 cc65 C compiler. It describes the memory layout, VIC20 specific header files,
24 available drivers, and any pitfalls specific to that platform.
26 Please note that VIC20 specific functions are just mentioned here, they are
27 described in detail in the separate <htmlurl url="funcref.html" name="function
28 reference">. Even functions marked as "platform dependent" may be available on
29 more than one platform. Please see the function reference for more
33 <sect>Binary format<p>
35 The standard binary output format generated by the linker for the VIC20 target
36 is a machine language program with a one line BASIC stub. This means that a
37 program can be loaded as BASIC program and started with RUN. It is of course
38 possible to change this behaviour by using a modified startup file and linker
42 <sect>Memory layout<p>
44 cc65 generated programs with the default setup run with the I/O area and the
45 kernal and BASIC ROM enabled (RAM at $A000 - $BFFF may be used
46 for the heap), which gives a usable memory range of $1000 - $1DFF.
47 All ROM entry points may be called directly without additional code.
53 The text screen is located at $1E00 (as in the standard setup).
56 The C runtime stack is located at $1DFF and growing downwards.
59 The C heap is located at the end of the program and grows towards the C
66 <sect>Platform specific header files<p>
68 Programs containing VIC20 specific code may use the <tt/vic20.h/ or <tt/cbm.h/
69 header files. Using the later may be an option when writing code for more than
70 one CBM platform, since it includes <tt/vic20.h/ and declares several functions
71 common to all CBM platforms.
74 <sect1>VIC20 specific functions<p>
76 The functions listed below are special for the VIC20. See the <htmlurl
77 url="funcref.html" name="function reference"> for declaration and usage.
84 <sect1>CBM specific functions<p>
86 Some functions are available for all (or at least most) of the Commodore
87 machines. See the <htmlurl url="funcref.html" name="function reference"> for
88 declaration and usage.
116 <sect1>Hardware access<p>
118 The following pseudo variables declared in the <tt/vic20.h/ header file do allow
119 access to hardware located in the address space. Some variables are
120 structures, accessing the struct fields will access the chip registers.
125 The <tt/VIC/ structure allows access to the VIC (the graphics
126 controller). See the <tt/_vic.h/ header file located in the include
127 directory for the declaration of the structure.
129 <tag><tt/VIA1, VIA2/</tag>
130 Access to the two VIA (versatile interface adapter) chips is available via
131 the <tt/VIA1/ and <tt/VIA2/ variables. The structure behind these variables
132 is explained in <tt/_6522.h/.
134 <tag><tt/COLOR_RAM/</tag>
135 A character array that mirrors the color RAM of the VIC20 at $9600.
141 <sect>Loadable drivers<p>
143 <sect1>Graphics drivers<p>
145 No graphics drivers are currently available for the VIC20.
148 <sect1>Extended memory drivers<p>
150 No extended memory drivers are currently available for the VIC20.
153 <sect1>Joystick drivers<p>
157 <tag><tt/vic20-stdjoy.joy/</tag>
158 Supports one standard joystick connected to the joysticks port of the VIC20.
164 <sect1>Mouse drivers<p>
166 No mouse drivers are currently available for the VIC20.
169 <sect1>RS232 device drivers<p>
171 No VIC1011 drivers are currently available for the VIC20.
181 <sect1>Passing arguments to the program<p>
183 Command line arguments can be passed to <tt/main()/. Since this is not
184 supported by BASIC, the following syntax was chosen:
187 RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
191 <item>Arguments are separated by spaces.
192 <item>Arguments may be quoted.
193 <item>Leading and trailing spaces around an argument are ignored. Spaces within
194 a quoted argument are allowed.
195 <item>The first argument passed to <tt/main/ is the program name.
196 <item>A maximum number of 10 arguments (including the program name) are
201 <sect1>Program return code<p>
203 The program return code (low byte) is passed back to BASIC by use of the
207 <sect1>Using extended memory<p>
209 The extended memory at $A000 may be added to the heap by using the following
213 /* Check for the existence of RAM */
214 if (PEEK(0xA000) == POKE(0xA000, PEEK(0xA000)+1)) {<br>
215 /* Add it to the heap */
216 _heapadd ((void *) 0xA000, 0x2000);
223 <sect>Bugs/Feedback<p>
225 If you have problems using the library, if you find any bugs, or if you're
226 doing something interesting with it, I would be glad to hear from you. Feel
227 free to contact me by email (<htmlurl url="mailto:uz@cc65.org"
228 name="uz@cc65.org">).
234 This software is provided 'as-is', without any expressed or implied
235 warranty. In no event will the authors be held liable for any damages
236 arising from the use of this software.
238 Permission is granted to anyone to use this software for any purpose,
239 including commercial applications, and to alter it and redistribute it
240 freely, subject to the following restrictions:
243 <item> The origin of this software must not be misrepresented; you must not
244 claim that you wrote the original software. If you use this software
245 in a product, an acknowledgment in the product documentation would be
246 appreciated but is not required.
247 <item> Altered source versions must be plainly marked as such, and must not
248 be misrepresented as being the original software.
249 <item> This notice may not be removed or altered from any source