Commodore VIC20 (aka VC20) specific information for cc65 <author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org"> Stefan A. Haubenthal, <htmlurl url="mailto:polluks@sdf.lonestar.org" name="polluks@sdf.lonestar.org"> <date>2004-09-13 <abstract> An overview over the VIC20 runtime system as it is implemented for the cc65 C compiler. </abstract>  <toc>  <sect>Overview This file contains an overview of the VIC20 runtime system as it comes with the cc65 C compiler. It describes the memory layout, VIC20 specific header files, available drivers, and any pitfalls specific to that platform. Please note that VIC20 specific functions are just mentioned here, they are described in detail in the separate <htmlurl url="funcref.html" name="function reference">. Even functions marked as "platform dependent" may be available on more than one platform. Please see the function reference for more information. <sect>Binary format The standard binary output format generated by the linker for the VIC20 target is a machine language program with a one line BASIC stub. This means that a program can be loaded as BASIC program and started with RUN. It is of course possible to change this behaviour by using a modified startup file and linker config. <sect>Memory layout cc65 generated programs with the default setup run with the I/O area and the kernal and BASIC ROM enabled (RAM at $A000 - $BFFF may be used for the heap), which gives a usable memory range of $1000 - $1DFF. All ROM entry points may be called directly without additional code. Special locations: <descrip> <tag/Text screen/ The text screen is located at $1E00 (as in the standard setup). <tag/Stack/ The C runtime stack is located at $1DFF and growing downwards. <tag/Heap/ The C heap is located at the end of the program and grows towards the C runtime stack. </descrip> <sect>Platform specific header files Programs containing VIC20 specific code may use the <tt/vic20.h/ or <tt/cbm.h/ header files. Using the later may be an option when writing code for more than one CBM platform, since it includes <tt/vic20.h/ and declares several functions common to all CBM platforms. <sect1>VIC20 specific functions There are currently no special VIC20 functions. <sect1>CBM specific functions Some functions are available for all (or at least most) of the Commodore machines. See the <htmlurl url="funcref.html" name="function reference"> for declaration and usage. <itemize> <item>cbm_close <item>cbm_closedir <item>cbm_k_setlfs <item>cbm_k_setnam <item>cbm_k_load <item>cbm_k_save <item>cbm_k_open <item>cbm_k_close <item>cbm_k_readst <item>cbm_k_chkin <item>cbm_k_ckout <item>cbm_k_basin <item>cbm_k_bsout <item>cbm_k_clrch <item>cbm_load <item>cbm_open <item>cbm_opendir <item>cbm_read <item>cbm_readdir <item>cbm_save <item>cbm_write <item>get_tv </itemize> <sect1>Hardware access The following pseudo variables declared in the <tt/vic20.h/ header file do allow access to hardware located in the address space. Some variables are structures, accessing the struct fields will access the chip registers. <descrip> <tag><tt/VIC/</tag> The <tt/VIC/ structure allows access to the VIC (the graphics controller). See the <tt/_vic.h/ header file located in the include directory for the declaration of the structure. <tag><tt/VIA1, VIA2/</tag> Access to the two VIA (versatile interface adapter) chips is available via the <tt/VIA1/ and <tt/VIA2/ variables. The structure behind these variables is explained in <tt/_6522.h/. <tag><tt/COLOR_RAM/</tag> A character array that mirrors the color RAM of the VIC20 at $9600. </descrip> <sect>Loadable drivers <sect1>Graphics drivers No graphics drivers are currently available for the VIC20. <sect1>Extended memory drivers No extended memory drivers are currently available for the VIC20. <sect1>Joystick drivers <descrip> <tag><tt/vic20-stdjoy.joy/</tag> Supports one standard joystick connected to the joysticks port of the VIC20. </descrip> <sect1>Mouse drivers No mouse drivers are currently available for the VIC20. <sect1>RS232 device drivers No VIC1011 drivers are currently available for the VIC20. <sect>Limitations <sect>Other hints <sect1>Passing arguments to the program Command line arguments can be passed to <tt/main()/. Since this is not supported by BASIC, the following syntax was chosen: <tscreen><verb> RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5 </verb></tscreen> <enum> <item>Arguments are separated by spaces. <item>Arguments may be quoted. <item>Leading and trailing spaces around an argument are ignored. Spaces within a quoted argument are allowed. <item>The first argument passed to <tt/main/ is the program name. <item>A maximum number of 10 arguments (including the program name) are supported. </enum> <sect1>Program return code The program return code (low byte) is passed back to BASIC by use of the <tt/ST/ variable. <sect1>Using extended memory The extended memory at $A000 may be added to the heap by using the following code: <tscreen><verb> /* Check for the existence of RAM */ if (PEEK(0xA000) == POKE(0xA000, PEEK(0xA000)+1)) { /* Add it to the heap */ _heapadd ((void *) 0xA000, 0x2000); } </verb></tscreen> <sect1>Interrupts The runtime for the VIC20 uses routines marked as <tt/.CONDES/ type 2 for interrupt handlers. Such routines must be written as simple machine language subroutines and will be called automatically by the interrupt handler code when they are linked into a program. See the discussion of the <tt/.CONDES/ feature in the <htmlurl url="ca65.html" name="assembler manual">. <sect>Bugs/Feedback If you have problems using the library, if you find any bugs, or if you're doing something interesting with it, I would be glad to hear from you. Feel free to contact me by email (<htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">). <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>