A former workmate who coded 'Conkers' for Rare explained that they ran out of work-RAM for the music/SFX player so they used part of the battery-backed (i.e. savegame) RAM. Nintendo were not too pleased, but being Rare they got away with it. Anyone else got stories of odd memory maps (I once used spare VRAM to store my hiscores).
Does that mean if the battery dies in Conkers, then your game suicides like a CPS3 board since it can't hold data anymore (+ anything store on it lost)?
It shouldn't have any effect on game play since the RAM is still powered by the GB and there's little chance that anything in the music engine uses the previous game state. Probably every NES game with battery backed SRAM uses most of it for general purpose WRAM.
I've always wanted an excuse to execute from VRAM. Assuming reads are atomic, and you stick to single-byte instructions, you could even handle running out of time - VRAM reads FF when inaccessible, which happens to be RST 38, a jump instruction. Storing sound data in save RAM is not a terrible idea, so long as you aren't modifying it often. Else you'd defeat the point of the write lock, likely corrupting the save if the battery died at the wrong time.
