This file contains an overview of the C128 runtime system as it comes with the cc65 C compiler. It describes the memory layout, C128-specific header files, available drivers, and any pitfalls specific to that platform.
Please note that C128-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 C128 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 the I/O area and the kernal ROM enabled. Note that this is a non standard memory layout, and that there is no "memory configuration index" for this layout. This means that special care has to be taken when changing the configuration, or calling any code that does this. The memory configuration register at $FF00 should be saved and restored instead of relying on the memory configuration index stored in the zero page.
The setup gives a usable memory range of $1C00 - $BFFF. Having just the kernal ROM mapped in means, that kernal entry points may be called directly, but using the BASIC ROM is not possible without additional code.
Special locations:
The text screen is located at $400 (as in the standard setup).
The C runtime stack is located at $BFFF, and growing downwards.
The C heap is located at the end of the program, and grows towards the C runtime stack.
Programs containing C128-specific code may use the c128.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 c128.h and declares several functions
common to all CBM platforms.
The functions listed below are special for the C128. See the function reference for declaration and usage.
The functions listed below are accelerator functions for the C128. See the function reference for declaration and usage.
Some functions are available for all (or at least most) of the Commodore machines. See the function reference for declaration and usage.
Some CPU related functions are available for some of the Commodore machines. See the function reference for declaration and usage.
The following pseudo variables declared in the c128.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 II (the graphics
controller). See the _vic2.h header file located in the include
directory for the declaration of the structure.
SIDThe SID structure allows access to the SID (the sound interface
device). See the _sid.h header file located in the include directory
for the declaration of the structure.
VDCThe VDC structure allows access to the VDC (the video display
controller). See the _vdc.h header file located in the include
directory for the declaration of the structure.
CIA1, CIA2Access to the two CIA (complex interface adapter) chips is available via
the CIA1 and CIA2 variables. The structure behind these variables
is explained in _6526.h.
COLOR_RAMA character array that mirrors the color RAM of the C128 at $D800.
The names in the parentheses denote the symbols to be used for static linking of the drivers.
The default drivers, tgi_stddrv (tgi_static_stddrv), point to c128-vdc.tgi (c128_vdc_tgi).
Note: The graphics drivers for the VDC are incompatible with the extended memory drivers using the VDC memory!
c128-hi.tgi (c128_hi_tgi)This driver features a resolution of 320×200 with two colors and an adjustable palette (that means that the two colors can be chosen out of a palette of the 16 VIC colors). Unlike BASIC 7.0, this driver puts its graphics data into the RAM behind the ROMs.
c128-vdc.tgi (c128_vdc_tgi)This driver was written by Maciej Witkowiak. It uses the 80-column display, and features a resolution of 640×200 with two colors and an adjustable palette (that means that the two colors can be chosen out of the 16 VDC colors).
c128-vdc2.tgi (c128_vdc2_tgi)This driver was written by Maciej Witkowiak. This driver uses the 80-column display, and features a resolution of 640×480 with two colors and an adjustable palette (that means that the two colors can be chosen out of the 16 VDC colors). The driver requires 64KB VDC RAM.
Note: The colors are translated from the definitions in the headers to correct
VDC values; so, please use definitions or VIC color numbers only. Colors
GRAY3 and BROWN are missing on the VDC; and, are translated to the
two colors missing from the VIC palette.
c128-efnram.emd (c128_efnram_emd)Extended memory driver for the C128 External Function RAM. Written and contributed by Marco van den Heuvel.
c128-georam.emd (c128_georam_emd)A driver for the GeoRam cartridge. The driver will always assume 2048 pages of 256 bytes each. There are no checks, so if your program knows better, just go ahead.
c128-ifnram.emd (c128_ifnram_emd)Extended memory driver for the C128 Internal Function RAM. Written and contributed by Marco van den Heuvel.
c128-ram.emd (c128_ram_emd)An extended memory driver for the RAM in page 1. The common memory area is excluded, so this driver supports 251 pages of 256 bytes each.
c128-ram2.emd (c128_ram2_emd)An extended memory driver for the RAM in pages 1-3. The common memory area
is excluded, so this driver supports up to 731 pages of 256 bytes each. The
driver can be used as a full replacement for c128-ram.emd, because RAM
in pages 2+3 is autodetected, but it's larger and there are not many
machines with RAM in banks 2+3, so it has been made a separate driver. The
additional code was contributed by Marco van den Heuvel.
c128-ramcart.emd (c128_ramcart_emd)A driver for the RamCart 64/128 written and contributed by Maciej Witkowiak. Will test the hardware for the available RAM.
c128-reu.emd (c128_reu_emd)A driver for the CBM REUs. The driver will test the connected REU to find out how much RAM is present.
c128-vdc.emd (c128_vdc_emd)A driver for the VDC memory of the C128, written and contributed by Maciej Witkowiak. Autodetects the amount of memory available (16 or 64K), and offers 64 or 256 pages of 256 bytes each. Note: This driver is incompatible with any of the graphics drivers using the VDC!
The default drivers, joy_stddrv (joy_static_stddrv), point to c128-stdjoy.joy (c128_stdjoy_joy).
c128-ptvjoy.joy (c128_ptvjoy_joy)Driver for the Protovision 4-player adapter originally written by Groepaz for the C64, and converted for the C128 by Uz. See Protovision shop for prices and building instructions. Up to four joysticks are supported.
c128-stdjoy.joy (c128_stdjoy_joy)Supports up to two joysticks connected to the standard joysticks ports of the C128.
The default drivers, mouse_stddrv (mouse_static_stddrv), point to c128-1351.mou (c128_1351_mou).
c128-1351.mou (c128_1351_mou)Supports a standard mouse connected to port #0 of the C128.
c128-inkwell.mou (c128_inkwell_mou)Supports the Inkwell Systems lightpens, connected to port #0 of the C128. It can read both the one-button 170-C and the two-button 184-C pens. (It can read other lightpens and light-guns that send their button signal to the joystick left-button pin or the paddle Y [up/down] pin.) It works on only the 40-column screen.
c128-joy.mou (c128_joy_mou)Supports a mouse emulated by a standard joystick, e.g. 1350 mouse, in port #1 of the C128.
c128-pot.mou (c128_pot_mou)Supports a potentiometer device, e.g. Koala Pad, connected to port #1 of the C128.
c128-swlink.ser (c128_swlink_ser)Driver for the SwiftLink cartridge. Supports up to 38400 baud, requires hardware flow control (RTS/CTS) and does interrupt driven receives. Note that, because of the peculiarities of the 6551 chip, together with the use of the NMI, transmits are not interrupt driven; and, the transceiver blocks if the receiver asserts flow control because of a full buffer.
The driver uses the RS232 variables and buffers of the kernal (buffers at $C00 and $D00).
The realtime clock functions use the CIA1 TOD clock. As that clock only stores
the time but not the date, the date set by clock_settime() is simply stored
inside the C library for retrieval in the same program via clock_gettime().
Command-line arguments can be passed to main(). Since this 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.
The runtime for the C128 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: