Doing mapper 69 (nice) instead, because Batman Return of the Joker is meant to be an awesome game.
Hmm... the PRG-ROM bank switching has a problem... but I really have nfi where/why/how...
It could be a bug in the CPU, but wow if I've gotten this far into the emulator without triggering it (afaict), then wow.
Mapper 69 progress: Only the bottom half of the B in Batman is being displayed, and it's in the wrong position, and it's using the wrong palette, but it's better than the great big nothing that I had before.
Apparently there are some behavioural differences between certain FME-7 cartridges, depending on whether or not they used battery-backed RAM.
Success! (kind of)
A lot of the game is working properly, but there are IRQ timing issues, which makes sense because I just kinda hacked the IRQ counting in.
The flickering is annoying and not meant to happen though. Hmm 😞
It's less flickery in the actual emulator than the gif shows, but still flickery enough.
Had a look at MMC5, and that thing is crazy.
_TWO_ extra audio channels?! And scanline counting, IRQs, and tons of other crazy stuff... yikes.
But I really want Castlevania 3 running...