Re: [cc65] Config file expressions (was: To Atari platform coordinator)

Hi,

On Fri, 29 Jul 2005, Christian Groessler wrote:

> I didn't
> change it to use __RESERVED_MEMORY__ instead of _graphmem_used yet. Will
> do this probably next week.

I've added this now to the CVS version. The value you set graphmode_used
to is now irrelevant. You have to set __RESERVED_MEMORY__ in the linker
script or the ld65 command line, like ld65 --define __RESERVED_MEMORY__=yyy ...

(Uz, wouldn't it be nice, if one could set this from the cl65 command
line? I think there is no way currently. Maybe by means like the gcc -Wl
and -Wa options, to pass switches explicitly to the assembler or linker?)

This is the text I've added to the Atari specific cc65 documentation, in
the "Graphics drivers" section:

-------------------------------------------------
  Currently there are no graphics drivers available for the Atari
  platform.  However, the runtime library provides a function named
  _graphics, with a mode parameter just like the DOS GRAPHICS command.
  This function will turn on the requested graphics mode.  There are
  currently no functions available to access the graphics memory. The
  access must be implemented manually.

  Many graphics modes require more memory than the text screen which is
  in effect when the program starts up. Therefore the programmer has to
  tell the program beforehand the memory requirements of the graphics
  modes the program intends to use.  This can be done with the
  __RESERVED_MEMORY__ linker config variable. The number specified there
  describes the number of bytes to subtract from the top of available
  memory as seen from the runtime library. This memory is then used by
  the screen buffer.

  The numbers for the different graphics modes presented below should
  only be seen as a rule of thumb. Since the screen buffer memory needs
  to start at specific boundaries, the numbers depend on the current top
  of available memory.  These numbers were determined by a BASIC
  program.


                     graphics mode   reserved memory
                     ___________________________________________________
                                 0                 1
                                 1                 1
                                 2                 1
                                 3                 1
                                 4                 1
                                 5               182
                                 6              1182
                                 7              3198
                                 8              7120
                                 9              7146
                                10              7146
                                11              7146
                                12               162
                                13                 1
                                14              3278
                                15              7120
                                16                 1
                                17                 1
                                18                 1
                                19                 1
                                20                 1
                                21               184
                                22              1192
                                23              3208
                                24              7146
                                25              7146
                                26              7146
                                27              7146
                                28               160
                                29                 1
                                30              3304
                                31              7146


          reserved memory required for different graphics modes

  The values of "1" are needed because the graphics command crashes if
  it doesn't have at least one byte available. This seems to be a bug of
  the Atari ROM code.
-------------------------------------------------

The last paragraph is of interest. The graphics function (opens the "S:"
device) crashes if there is no room avaiable between MEMTOP and APPMHI. I
don't know why...

regards,
chris


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