> I suposse I could re-join both 68k ROMs and try make a comparison/quick disassembly
> and check for any differences against the Sonic 1 Rev01's disassembly. But where can
> I find the code that deals with the extra z80 ROM within MAME's source code? This
> might give me an insight on the "minimals" for booting the game.
all the handling for the extra hardware is in drivers/megaplay.cpp but as I said, I don't really trust it to be correct tho, it just kind of works right now, there are some bits that are clearly not right (and there's absolutely no understanding / support for having more than 1 cartridge inserted right now, the real hardware could cycle games like NeoGeo MVS)
you could compare a disassembly of the 2 versions (the actual binary will be significantly different, it's not a hack of the game, it's a complete recompile, doesn't have any of the 'slower' levels, has strict time limits, takes out 1-ups, takes out special stages etc)
you're pretty much on your own with this kind of thing beyond what i've pointed out tho.