Omega Race runs in simulation

I've updated the hardware description on spies to match the actual behavior
of the hardware using a simulation. I have enough of it working now that the
game is playable. The absolute postion encoder is weird. I hadn't read Bryan
Edewaard's optical encoder hack before I started on this, and after messing
with trying to get the encoder to work in simulation, I was impressed by the
work he must have put in to get it working!

        The encoder is a 64 position switch (or pot/AtoD conv)
        so unlike the quadrature inputs on Atari and Sega games,
        Omega Race's controller is an absolute angle.

        The mapping is bizzare, here is the encoding for an 8-way
        mapping of encoder 1

                    00 1C 40
                      \|/
                    3C-+- FC
                      /|\
                    80 9C C0

For some reason, they scrambled the bit inputs only on the 1 player controller...
I've spent more time figuring out the stupid encoder than coding the rest of
the simulation!

There also seems to be either a subtle difference in the DVG of the Midway board
and the one simulated in Eric Smith's code. It appears that the final relative
position in the counters may be off by one after a display subroutine call in
Omega Race. The symptom is that a row of symbols (like a line of text) 'droop'
towards the lower right.

Anyway, most of the display list traversal code from Eric's Atari simulator worked
without modification, so I guess Midway's design was pretty close to Atari's :-)
Received on Wed Jul 23 10:48:08 1997