I've made good progress on screen timing and now can get pixel accurate frames even for timing sensitive games like Speedway above.
I also figured out the (probably) correct emulation for Blockout, which is much simpler and more realistic then what I was doing before. The key is that the VBL flag bit is reset upon read, not upon end of VBL. It's more of a 'VBL needs servicing' flag then a 'VBL in progress' flag. I probably should have guessed this earlier since the sound bit works the same way.
There are still a few finer details that need to be sorted out, but I think all the major timing challenges are dealt with now.
Here is one of the best homebrew games for the O2 that is now finally working in BizHawk. This is one of those games that relies on a lot of hardware edge cases and revealed several bugs in the core.
Kill the Attacking Aliens uses some non-intuitive properties of quads to get some really detailed graphics effects that are unique to this game. It's one of those impressive homebrews that could really have helped define a system if it had come out in it's actual lifetime.
This is probably one of the few O2 games that really would be interesting to TAS, so I'm glad it's looking correct now.I made quite a few bug fixes: - fixed collision detection - fixed 12k games - tuned the colors a bit - fixed some characters in the built in set - Fixed sound interrupts @phoenix1291: thanks for testing. I think the graphics at the bottom of frogger brazil are just because it's PAL 60 (BR) but emulated as PAL 50 (more scanlines), I haven't added a mode for that yet. Some of the other bugs should be cleared up though.
