JEO 41/46
   ||  Temporary Sanity Travails
   ||  By: Damien M. Jones
\__//  dmj@fractalus.com
//// tsd: A Year Ago
In January of 1995, Bryan Edewaard and I (Damien Jones) left our jobs
in Dallas, Texas and moved to Florida to start our own business,
temporary sanity designs. Our intent was to write a game for the PC -
after all, since everybody else seemed to be doing such a lousy job of
it, we could do it and maybe make a bit of cash in the process.
For several months we worked on a fast 3D polygon engine, although
without a final goal firmly in mind we didn't get too far (then). In
April, we got the idea that maybe we could do something for Atari's
game console, the Jaguar. This was Atari's attempt to get back into
the game console market - the market they had once dominated with the
Atari 2600. Both Bryan and I had experience with Atari computers in
the past, and we were somewhat familiar with the company.
//// The 2600
What we suggested to Atari was that maybe somebody should write an
emulator for the Jaguar that would run the original games from the
2600 on the Jaguar - sort of like Activision's 2600 Action Pack for
Windows. We suggested that that somebody be us. We told them one of us
(Bryan) had already written a 6502 CPU emulator (for the Atari ST), so
half the work was already done.
Atari seemed to like the idea, but they weren't too sure about us.
After all, when a company with a name like temporary sanity designs
sends you a project proposal, asking for money and a free development
system (we sure couldn't afford $8,000 for a Jaguar development kit),
you're inclined to treat the whole thing with a bit of skepticism.
They asked for a little "demonstration" that we could produce
something.
This presented something of a problem for us, because while Bryan had
written a 6502 CPU emulator, he'd sort of, well, lost the source code
to it. We didn't have it, Atari wanted a demo in fairly short order,
and we didn't want to waste a lot of development time writing a demo
for Atari computers that would be useless on the Jaguar. But we did,
in fact, produce a working demo of the game Combat running on an Atari
TT computer. It wasn't 100%, but it was Combat.
Atari (or at least, the person we'd been dealing with) was impressed.
They sent out a Jaguar development system on loan for sixty days. We
had that long to produce enough of a working demo to show that the
entire project was feasible. Keep in mind, neither Bryan nor I had
ever seen programming details for the Jaguar (they're covered by NDA).
Not only had we never programmed the Jaguar before, but writing an
emulator is a difficult task. (Our demo of Combat was, shall I say,
very specific to Combat.) One of the reasons an emulator is so hard to
write, particularly when dealing with the 2600, is that so much of the
program has to be fully working before you see anything on the screen.
Virtually the entire 6502 CPU emulator, and a large part of the custom
hardware emulator, must be written and fully debugged before anything
intelligible appears.
To make things even more fun, the 2600 produces video one scanline at
a time. Computers of today produce video one frame at a time. That is,
even if the CPU does absolutely nothing, the video hardware will draw
a full screen image. The CPU only needs to get involved if there needs
to be some change from one frame to the next. The 2600 can only
generate one line by itself. If something is to be different between
one screen line and the next, the CPU needs to change data in the
video hardware. Because of this tight coupling between the CPU and the
display, the slightest mistake in the CPU emulator immediately affects
what appears on the screen.
I mention this, only so you will understand how technically difficult
writing a 2600 emulator is. We had a mere 60 days to produce
"evidence" that the project was feasible. Our work was definitely cut
out for us.
... THEY: The Hearsay Experts for You.
--- JetMail 0.99beta22
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