[GEM Development] SDPSC9 updated

[John Elliott]

  I've updated the VGA driver source (SDPSC9) that's on my site.

  Note that the actual driver is (almost) unchanged. What's different is the
way it's built. I've split the source code up into modules using the same
organization as the original DRI driver source, and (where appropriate) 
used DRI's source (via Chris Barnes' VGA driver) rather than my disassembled 
version.
  Having done that, I was able without too much work to copy the source for
the 640x350 EGA driver into my tree as well. So there's now a version of the
EGA driver (SDEHF9) that supports codepages and the high-resolution timer.

  Weird trivia:
* If LINK86 is rejecting your INP files for no apparent reason, stick 128
 dummy bytes on the end. It only reads up to a multiple of 128 bytes, so
 up to 127 bytes at the end will be ignored.

* The SDPSC9 I disassembled was using version 21 of the mouse driver, but
 the SDEHF9 was only on version 20.

* The driver source tree we've got is several versions earlier than GEM 3.1
 (for example, the mouse driver is version 16). But it also contains some
 things that appear to be bugfixes but aren't present in the GEM 3.1
 drivers. They're mostly commented "jn" plus various dates in Autumn 1987.

-- 
John Elliott