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<title>Commodore 128 specific information for cc65
<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
<date>2003-12-14

<abstract>
An overview over the C128 runtime system as it is implemented for the cc65 C
compiler.
</abstract>

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<sect>Overview<p>

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 <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<p>

The standard binary output format generated by the linker for the C128 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<p>

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 case has to be taken when changing the configuration, or calling any
code that does this. The memory configuration register at &dollar;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 &dollar;1C00 - &dollar;CFFF. 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:

<descrip>
  <tag/Text screen/
  The text screen is located at &dollar;400 (as in the standard setup).

  <tag/Stack/
  The C runtime stack is located at &dollar;CFFF and growing downwards.

  <tag/Heap/
  The C heap is located at the end of the program and grows towards the C
  runtime stack.

</descrip><p>



<sect>Platform specific header files<p>

Programs containing C128 specific code may use the <tt/c128.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/c128.h/ and declares several functions
common to all CBM platforms.


<sect1>C128 specific functions<p>

The functions listed below are special for the C128. See the <htmlurl
url="funcref.html" name="function reference"> for declaration and usage.

<itemize>
<item>toggle_videomode
<item>c64mode
<item>fast
<item>slow
</itemize>


<sect1>CBM specific functions<p>

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<p>

The following pseudo variables declared in the <tt/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.

<descrip>

  <tag><tt/VIC/</tag>
  The <tt/VIC/ structure allows access to the VIC II (the graphics
  controller). See the <tt/_vic2.h/ header file located in the include
  directory for the declaration of the structure.

  <tag><tt/SID/</tag>
  The <tt/SID/ structure allows access to the SID (the sound interface
  device). See the <tt/_sid.h/ header file located in the include directory
  for the declaration of the structure.

  <tag><tt/VDC/</tag>
  The <tt/VDC/ structure allows access to the VDC (the video display
  controller). See the <tt/_vdc.h/ header file located in the include
  directory for the declaration of the structure.

  <tag><tt/CIA1, CIA2/</tag>
  Access to the two CIA (complex interface adapter) chips is available via
  the <tt/CIA1/ and <tt/CIA2/ variables. The structure behind these variables
  is explained in <tt/_6526.h/.

  <tag><tt/COLOR_RAM/</tag>
  A character array that mirrors the color RAM of the C64 at &dollar;D800.

</descrip><p>



<sect>Loadable drivers<p>

<sect1>Graphics drivers<p>

Note: The graphics drivers for the VDC are incompatible with the extended
memory drivers using the VDC memory!

<descrip>
  <tag><tt/c128-vdc.tgi/</tag>
  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).

  <tag><tt/c128-vdc2.tgi/</tag>
  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.
</descrip><p>

Note: The colors are translated from definitions in headers to correct VDC values
so please use definitions or VIC color numbers only. Colors <tt/GRAY3/ and <tt/BROWN/ are
missing on VDC and are translated to the two colors missing from VIC palette.

<sect1>Extended memory drivers<p>

<descrip>

  <tag><tt/c128-georam.emd/</tag>
  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.

  <tag><tt/c128-ram.emd/</tag>
  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.

  <tag><tt/c128-ramcart.emd/</tag>
  A driver for the RamCart 64/128 written and contributed by Maciej Witkowiak.
  Will test the hardware for the available RAM.

  <tag><tt/c128-reu.emd/</tag>
  A driver for the CBM REUs. The driver will determine from the connected REU
  if it supports 128KB of RAM or more. In the latter case, 256KB are assumed,
  but since there are no range checks, the application can use more memory if
  it has better knowledge about the hardware than the driver.

  <tag><tt/c128-vdc.emd/</tag>
  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!

</descrip><p>


<sect1>Joystick drivers<p>

<descrip>

  <tag><tt/c128-ptvjoy.joy/</tag>
  Driver for the Protovision 4-player adapter originally written by Groepaz
  for the C64 and converted for the C128 by me. See <htmlurl
  url="http://www.protovision-online.de/hardw/hardwstart.htm"
  name="http://www.protovision-online.de/hardw/hardwstart.htm"> for prices and
  building instructions. Up to four joysticks are supported.

  <tag><tt/c128-stdjoy.joy/</tag>
  Supports up to two joysticks connected to the standard joysticks port of
  the C128.

</descrip><p>



<sect1>Mouse drivers<p>

Currently no drivers available (in fact, the API for loadable mouse drivers
does not exist).


<sect1>RS232 device drivers<p>

<descrip>

  <tag><tt/c128-swlink.ser/</tag>
  Driver for the SwiftLink cartridge. Supports up to 38400 baud, hardware flow
  control (RTS/CTS) and 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
  &dollar;C00 and &dollar;D00).

</descrip><p>



<sect>Limitations<p>



<sect>Other hints<p>

<sect1>Passing arguments to the program<p>

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<p>

The program return code (low byte) is passed back to BASIC by use of the
<tt/ST/ variable.


<sect1>Interrupts<p>

The runtime for the C128 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<p>

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<p>

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>




