Re: 5.25 drive emulator

[rdippold@qualcomm.com (Ron "Asbestos" Dippold)]

stu1222@alpha.wright.edu (General Unix Accounts) writes:
>Ok, this is really getting on my nerves.  STM can do Apple II disk images
>on a mac and do a complete emulation.  Why cant anyone out there write a
>5.25 disk emulator for the GS?  This way we can store and run those
>classic 4,6,8, and 12 sided games off of a Hard Drive.  Also, those 5.25's

DOS 3.3 Launcher does this to a certain extent.  However you can't
have a general 5.25 disk emulator without some serious weirdness going
on.  Something like DOS 3.3 launcher just needs to provide
RWTS/IOB/etc. routines which software JSRs to, and some values in
fixed memory locationss.  For a real 5.25 emulator, you'd need to
intercept and emulate all the bizarre Disk ][ ports and try to do
something meaningful with them.

It's actually not horribly bad with normal reads and writes, if you
store everything in nibbilized track format.  However, intercepting
them is a big problem, especially with games that decrypt or unpack
portions of themselves as needed.  As far as I know there's no
mechanism on the IIgs that will let you intercept and transfer control
given an access to a specific memory address, as there is on the
80386.  I I'm wrong and such a mechanism exists, then you could trap a
read or write and try to do the appropriate thing.
-- 
"You won't get away with this," said Cutwell. He thought for a bit and
added, "Well, you will probably get away with it, but you'll feel bad about
it on your deathbed and you'll wish -- " He stopped talking.
  -- Terry Pratchett, Mort