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 function reference. Even functions marked as "platform dependent" may be available on more than one platform. Please see the function reference for more information.
The standard binary output format generated by the linker for the VIC20 target is a machine language program with a one line BASIC stub, which calls the machine language part via SYS. 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.
cc65 generated programs with the default setup run with unexpanded memory (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:
The text screen is located at $1E00 (as in the standard setup).
The C runtime stack is located at $1DFF and growing downwards.
The C heap is located at the end of the program and grows towards the C runtime stack.
Programs containing VIC20-specific code may use the vic20.h or cbm.h
header files. Using the later may be an option when writing code for more than
one CBM platform, since it includes vic20.h and declares several functions
common to all CBM platforms.
There are currently no special VIC20 functions.
Some functions are available for all (or at least most) of the Commodore machines. See the function reference for declaration and usage.
The following pseudo variables declared in the 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.
VICThe VIC structure allows access to the VIC (the graphics
controller). See the _vic.h header file located in the include
directory for the declaration of the structure.
VIA1, VIA2Access to the two VIA (versatile interface adapter) chips is available via
the VIA1 and VIA2 variables. The structure behind these variables
is explained in _6522.h.
COLOR_RAMA character array that mirrors the color RAM of the VIC20 at $9600.
The names in the parentheses denote the symbols to be used for static linking of the drivers.
vic20-hi.tgi (vic20_hi_tgi)This driver features a resolution of 160×192 with two colors. The background can be chosen from a sixteen-color palette. The foreground can be chosen from an eight-color palette.
The driver will use memory from addresses $1000 to $1FFF as a graphics buffer. Therefore, the VIC-20 must have, at least, 8K of expansion RAM.
Programs that use this driver must be linked by the vic20-tgi.cfg
configuration file. It will link a special header into the program.
That header will do the housekeeping that's needed by TGI.
An example command line:
cl65 -D DYN_DRV=0 -t vic20 -C vic20-tgi.cfg samples/mandelbrot.c
When the program starts, it will move itself up in RAM, to make room for the buffer. When the program finishes, it will reset the BASIC interpreter. That means that graphics pictures won't be preserved between the executions of programs. Also, the graphics buffer shares RAM with the text screen. If a picture must be saved, then a program must put it somewhere else (such as a disk file) before returning to the text mode.
vic20-rama.emd (vic20_rama_emd)A driver for any RAM at $A000-$BFFF. Supports 32 256 byte pages. Written and contributed by Marco van den Heuvel.
vic20-georam.emd (vic20_georam_emd)A driver for the Berkeley Softworks GeoRam cartridge connected by means of the MasC=erade c64 cartridge adapter. The driver will determine the available RAM from the connected cartridge. It supports 64KB up to 2048KB of RAM.
The default drivers, joy_stddrv (joy_static_stddrv), point to vic20-stdjoy.joy (vic20_stdjoy_joy).
vic20-stdjoy.joy (vic20_stdjoy_joy)Supports one standard joystick connected to the joysticks port of the VIC20.
vic20-ptvjoy.joy (vic20_ptvjoy_joy)Driver for the Protovision 4-player adapter contributed by Groepaz. See the Protovision shop for prices and building instructions. Up to three joysticks are supported.
No mouse drivers are currently available for the VIC20.
No VIC1011 drivers are currently available for the VIC20.
The CTRL key cannot be used to type most control characters, entering an Esc is not possible.
Command-line arguments can be passed to main(). Since that is not
supported directly by BASIC, the following syntax was chosen:
RUN:REM ARG1 " ARG2 IS QUOTED" ARG3 "" ARG5
main() is the program name.The program return code (low byte) is passed back to BASIC by use of the
ST variable.
BLK5 memory may be added to the heap by using the following code:
/* Check for the existence of RAM */
if (PEEK(0xA000) == POKE(0xA000, PEEK(0xA000)+1)) {
/* Add it to the heap */
_heapadd ((void *) 0xA000, 0x2000);
}
The runtime for the VIC20 uses routines marked as .INTERRUPTOR 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 .CONDES
feature in the
assembler manual.
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: