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<title>c64 specific information for cc65
<author>Ullrich von Bassewitz, <htmlurl url="mailto:uz@cc65.org" name="uz@cc65.org">
<date>2003-09-23

<abstract>
An overview over the C64 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 C64 runtime system as it comes with the
cc65 C compiler. It describes the memory layout, C64 specific header files,
available drivers, and any pitfalls specific to that platform.

Please note that C64 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 C64 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 (memory under the kernal may be used for graphics or as
extended memory - see the sections about graphics and extended memory
drivers). The BASIC ROM is disabled, which gives a usable memory range of
&dollar;0800 - &dollar;CFFF. This 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 C64 specific code may use the <tt/c64.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/c64.h/ and declares several functions
common to all CBM platforms.


<sect1>C64 specific functions<p>

The functions listed below are special for the C64. See the <htmlurl
url="funcref.html" name="function reference"> for declaration and usage.

<itemize>
<item>get_ostype
</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/c64.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/CIA1, CIA2/</tag>
  Access to the two CIA (complex interface adapater) chips is available via
  the <tt/CIA1/ and <tt/CIA2/ variables. The structure behind these variables
  is explained in <tt/_cia.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>

All available graphics drivers for the TGI interface will use the space below
the I/O area and kernal ROM, so you can have hires graphics in the standard
setup without any memory loss or need for a changed configuration.

<descrip>
  <tag><tt/c64-hi.tgi/</tag>
  This driver features a resolution of 320*200 with two colors and an
  adjustable palette (that means that the two colors can be choosen out of a
  palette of the 16 C64 colors).
</descrip><p>


<sect1>Extended memory drivers<p>

<descrip>

  <tag><tt/c64-georam.emd/</tag>
  A driver for the GeoRam cartridge. The driver will always assume 2048 pages
  of 256 bytes each.

  <tag><tt/c64-ram.emd/</tag>
  A driver for the hidden RAM below the I/O area and kernal ROM. Supports 48
  256 byte pages. Please note that this driver is incompatible with any of the
  graphics drivers!

  <tag><tt/c64-ramcart.emd/</tag>
  A driver for the RamCart 64/128. Will test the hardware for the available
  RAM.

  <tag><tt/c64-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/c64-vdc.emd/</tag>
  A driver for the VDC memory of the C128. Can be used if the program is
  running in C64 mode of the C128. Autodetects the amount of memory available
  (16 or 64K) and offers 64 or 256 pages of 256 bytes each.

</descrip><p>


<sect1>Joystick drivers<p>

<descrip>

  <tag><tt/c64-stdjoy.joy/</tag>
  Supports up to two standard joysticks connected to the joysticks port of
  the C64.

</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/c64-swlink.ser/</tag>
  Driver for the SwiftLink cartridge. Supports up to 38400 baud, hardware flow
  control (RTS/CTS) and interrupt driven receives.

</descrip><p>



<sect>Other hints<p>




<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>



