Reply 20 of 42, by 640K!enough
wrote:AFAIK MMA only serves as bus address decoder for OPL3. For all purposes it can be considered transparent if we are only concerned with OPL3 (and if mixer is alreadty set up properly).
4 MMA chip regs follow 4 OPL3 regs and the method of accessing its state mirrors OPL3.
I may have had the address ranges slightly wrong (I will have to look into it, if there is a need), but there are three main components that software typically addresses on GSS cards: OPL3, MMA (digital audio, MIDI, joystick) and the control chip. All three are required for the usual routines to identify a Gold card of some sort. If my memory isn't too hazy, the MMA is usually checked first, followed by OPL3, and lastly, the control chip.
To complicate matters, GSS level 1 cards don't have a control chip. For level 2 cards, the control chip may be at an address just after MMA, or may overlap the second set of OPL3 addresses (38A, was it?). That last option was referred to as "phantom control", and it was necessary to "disable" the OPL3 before addressing the control chip.
Some of this is unnecessary information for your purposes, but the point is that no properly GSS-compliant software will find a card without something acting like an MMA. If you fool the detection routines, what do you do if/when they finally try to make use of the MMA that they think is there?