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Sega, schematics, sound and color
Been spending some time trying to figure out some remaining Out Run/X-Board/Y-Board details from schematics and PAL dumps. A special thanks to Colin Davies for digging up some Out Run schematics — these have been quite helpful in nailing down some details. For example, the priorities between the two roads in Out Run were not known, but thanks to the schematics I was able to identify the logic device that controls it. Once we got a dump of that, I was able to get things working correctly, fixing a few minor priority cases that weren't correct (though I was mostly right :-)
One other thing I've been looking at is the Y-board sprite priorities. It is clear from the schematics that they hacked in a 7-bit priority value for the line sprites (top layer). Unfortunately, those 7 bits go into a black box custom part that does the mixing with the 16 bits of fancy Y-board rotato-sprites, so a lot of guessing was involved. What makes it even harder is that for the most part, the games make very little use of the priority. It is mainly used for your ship in Galaxy Force 2 and for some of the zoom in/zoom out effects in G-Loc and Strike Fighter. I don't have a full explanation of what the 7 bits of priority do, but I have something that seems to be mostly correct.
A baffling aside in this instance. I was searching for cases where the priority was being used and found that it was used in the static title screen on Strike Fighter. What's really bizarre is that periodically during attract mode, the title screen will play some missile sounds and explosions. Well, underneath the title screen, there is actually some graphics animating missiles and explosions, but all of that is over-rendered by the title screen. Even more confusing is that as far as I can tell, this is entirely deliberate. Both the title screen and the missile/explosion sprites are drawn with the fancy Y-board sprite generator, where the priorities don't matter. And even if they did, the title screen is quite clearly higher priority than everything else. If someone knows where to observe a real Strike Fighter, I would be immensely curious to confirm my suspicions.
On non-Sega notes, yes, I fixed Q-Sound for the Capcom games. Stop bothering me.
On a more interesting non-Sega note, I came across this auction for a Driver's Edge cabinet. Now, Driver's Edge is quite the rare game to find, and was also quite the bitch to get working because unlike the other 32-bit Strata games, it uses a pair of TMS320C31s to drive the polygon engine, and some extensions to the standard Incredible Technologies blitter chip as well. Anyway, this auction had the first actual Driver's Edge screenshots I'd seen. And guess what? It turns out I had red and blue swapped in the driver! Once I fixed that, I can match the screenshots pretty much exactly, which is a big relief because there was a lot of subtle stuff involved in making that driver work!