The NMK004 state machine supports:
- Six FM channels; each pair of them shares one of the three YM2203 voices.
- Three PSG channels, each one using one of the PSG voices of the YM2203.
- Eight Effects channels, which can use the total eight voices provided by the two Oki M6295 to play sample-based sounds like drums (but they are also sometimes used to play effects not music related).
- Direct triggering of Oki M6295 samples (this is not strictly part of the state machine)
Current simulation status is as follows:
- Not done yet.
- Partially done. The state machine works and seems to play notes at the correct speed. However, the pitch of the notes is way off.
- Seems to be ok.
- Is mostly ok but there are some strange things here and there - difficult to say if it's a simulation error or just how it's supposed to be.
I am growing more and more convinced that the internal ROM of the NMK004 is the same in all games. A few of the games in the driver have additional protection issues, but at this point I don't think they are related to the NMK004.