I am working on a MMC2 mapper for my emulator and I am getting some strange glitches that I've spent quite a while trying to figure out.I have been through the wiki page on MMC2 with a fine tooth comb and I think I've implemented everything as it states.
Here are some screenshots for Mike Tyson's Punch Out.
When the first screen comes up all is well:
Problems start happening here on the title page:
It gets worse when the game actually starts as half the ring is missing (which causes the game to crash, probably because sprite zero is not hitting)
The two things I have been focusing on are the bank switching in the mapper itself and also making sure that the tile byte fetches in the PPU are happening at the right pixels. As far as I can tell there isn't anything wrong with those things.
I've had a look at similar threads about MMC2 from the past but I haven't come across anyone with this particular problem. If anyone has any ideas it would be much appreciated.
