<!doctype linuxdoc system>

<article>
<title>Commodore 128-specific information for cc65
<author><url url="mailto:uz@cc65.org" name="Ullrich von Bassewitz">,<newline>
<url url="mailto:polluks@sdf.lonestar.org" name="Stefan A. Haubenthal">

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

<!-- Table of contents -->
<toc>

<!-- Begin the document -->

<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 <url 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, 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.


<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 care 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;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:

<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;BFFF, 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 <url
url="funcref.html" name="function reference"> for declaration and usage.

<itemize>
<item>videomode
<item>c64mode
</itemize>


<sect1>C128-specific accelerator functions<p>

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

<itemize>
<item>detect_c128
<item>detect_scpu
<item>get_c128_speed
<item>get_scpu_speed
<item>set_c128_speed
<item>set_scpu_speed
</itemize>


<sect1>CBM-specific functions<p>

Some functions are available for all (or at least most) of the Commodore
machines. See the <url 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_k_tksa
<item>cbm_k_second
<item>cbm_load
<item>cbm_open
<item>cbm_opendir
<item>cbm_read
<item>cbm_readdir
<item>cbm_save
<item>cbm_write
<item>get_tv
<item>waitvsync
</itemize>


<sect1>CBM specific CPU functions<p>

Some CPU related functions are available for some of the Commodore
machines. See the <url url="funcref.html" name="function reference"> for
declaration and usage.

<itemize>
<item>fast
<item>slow
<item>isfast
</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 C128 at &dollar;D800.

</descrip><p>



<sect>Loadable drivers<p>

The names in the parentheses denote the symbols to be used for static linking of the drivers.


<sect1>Graphics drivers<p>

The default drivers, <tt/tgi_stddrv (tgi_static_stddrv)/, point to <tt/c128-vdc.tgi (c128_vdc_tgi)/.

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

<descrip>

  <tag><tt/c128-hi.tgi (c128_hi_tgi)/</tag>
  This driver features a resolution of 320&times;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.

  <tag><tt/c128-vdc.tgi (c128_vdc_tgi)/</tag>
  This driver was written by Maciej Witkowiak. It uses the 80-column display,
  and features a resolution of 640&times;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 (c128_vdc2_tgi)/</tag>
  This driver was written by Maciej Witkowiak. This driver uses the 80-column
  display, and features a resolution of 640&times;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 the definitions in the headers to correct
VDC values; so, please use definitions or VIC color numbers only. Colors
<tt/GRAY3/ and <tt/BROWN/ are missing on the VDC; and, are translated to the
two colors missing from the VIC palette.


<sect1>Extended memory drivers<p>

<descrip>

  <tag><tt/c128-efnram.emd (c128_efnram_emd)/</tag>
  Extended memory driver for the C128 External Function RAM.
  Written and contributed by Marco van den Heuvel.

  <tag><tt/c128-georam.emd (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-ifnram.emd (c128_ifnram_emd)/</tag>
  Extended memory driver for the C128 Internal Function RAM.
  Written and contributed by Marco van den Heuvel.

  <tag><tt/c128-ram.emd (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-ram2.emd (c128_ram2_emd)/</tag>
  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 <tt/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.

  <tag><tt/c128-ramcart.emd (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 (c128_reu_emd)/</tag>
  A driver for the CBM REUs. The driver will test the connected REU to find
  out how much RAM is present.

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

The default drivers, <tt/joy_stddrv (joy_static_stddrv)/, point to <tt/c128-stdjoy.joy (c128_stdjoy_joy)/.

<descrip>

  <tag><tt/c128-ptvjoy.joy (c128_ptvjoy_joy)/</tag>
  Driver for the Protovision 4-player adapter originally written by Groepaz
  for the C64, and converted for the C128 by Uz. See <url
  url="http://www.protovision-online.de/hardw/4_player.php?language=en"
  name="Protovision shop"> for prices and building instructions. Up to four
  joysticks are supported.

  <tag><tt/c128-stdjoy.joy (c128_stdjoy_joy)/</tag>
  Supports up to two joysticks connected to the standard joysticks ports of
  the C128.

</descrip><p>



<sect1>Mouse drivers<p>

The default drivers, <tt/mouse_stddrv (mouse_static_stddrv)/, point to <tt/c128-1351.mou (c128_1351_mou)/.

<descrip>

  <tag><tt/c128-1351.mou (c128_1351_mou)/</tag>
  Supports a standard mouse connected to port #0 of the C128.

  <tag><tt/c128-inkwell.mou (c128_inkwell_mou)/</tag>
  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.

  <tag><tt/c128-joy.mou (c128_joy_mou)/</tag>
  Supports a mouse emulated by a standard joystick, e.g. 1350 mouse, in port
  #1 of the C128.

  <tag><tt/c128-pot.mou (c128_pot_mou)/</tag>
  Supports a potentiometer device, e.g. Koala Pad, connected to port #1 of
  the C128.

</descrip><p>


<sect1>RS232 device drivers<p>

<descrip>

  <tag><tt/c128-swlink.ser (c128_swlink_ser)/</tag>
  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
  &dollar;C00 and &dollar;D00).

</descrip><p>



<sect>Limitations<p>


<sect1>Realtime clock<p>

The realtime clock functions use the CIA1 TOD clock. As that clock only stores
the time but not the date, the date set by <tt/clock_settime()/ is simply stored
inside the C library for retrieval in the same program via <tt/clock_gettime()/.



<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 directly 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/.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 <tt/.CONDES/
feature in the <url url="ca65.html" name="assembler manual">.



<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>
