[Coco] CDi Emulator

[Joel Ewy]

Another thought on building an open source MM/1 / CD-i emulator is to
start with MESS.  I'm sure Tim Lindner can give us more insight here,
but I see that MESS emulates the Atari ST series.  It also emulates so
much other diverse hardware, it makes me wonder if it doesn't already
have code for any of the chips we would need:

WD37C65 FDC
Brooktree video DAC / Palette controller
MC68901 MFP (1 on CPU board, 1 on I/O board) <-Atari ST has this chip
MC68681 Serial (on I/O board)
MC68230 PIT (on I/O board)
WD33C93 SCSI (on I/O board)
DS1287 RTC (on I/O board)
AD7569 ADC/DAC (2x on I/O board)

The fact that the Atari ST and Mac are emulated means that there is a
68000 CPU, which would only need slight modification to add the extra
features of the 68070 that are actually used by the MM/1 or the TC-70,
unless you insist on accurate instruction timing.  I think that the
biggest job for anyone trying to implement an MM/1 / TC-70 / CD-i
emulator would be to emulate the 66470 VSC.  It's well documented though. 

If you could find or write OS-9 drivers that would work with alternate
hardware that is available in the the MESS codebase, you wouldn't really
need to emulate all the same chips right away.  For instance, I can't
think of any MM/1 software aside from the hard disk driver module itself
that actually cares that the MM/1 uses the WD33C93 rather than some
other chip.  If some other computer emulated in MESS has a different
SCSI controller, and you can dig up an old OS-9 driver for it, you
wouldn't have to implement the 33C93 right away.  It's really the 66470
VSC that makes the MM/1 or the TC-70 or the CD-i.  Even so, any kind of
emulated computer that runs OS-9/68K would be a big step in the
direction of emulation of these three similar systems.  I'm not aware at
the moment of any emulator that actually runs any 68000 version of
OS-9.  Of course I'd love to be proven wrong.  I tried the Atari version
of OS-9 on ARANYM, and probably also some MS-Windows-based emulators
with no joy.  I don't remember trying MESS though...

JCE