#762 Can't set PRG-RAM to 0 with NES 2.0 header

[Kef Schecter]

There is a glitch the player can perform in TMNT to access areas that aren't on the map. When this happens, the game sometimes accesses the PRG-RAM area. The actual game contains no PRG-RAM, so this should yield open-bus behavior. However, FCEUX assumes that 8 KB of PRG-RAM is present, even with an NES 2.0 header to explicitly set the PRG-RAM size to 0. Thus, the game behaves differently than it does on hardware while executing the glitch.

[zeromus]

was this resolved by r3321 or r3322?

[Alex W. Jackson]

Setting the RAM size in a NES 2.0 header should now work for MMC1 games such as TMNT.

Cartridge CHR RAM is handled in a centralized way by FCEUX (although somewhat inconsistently between NES 1.0, NES 2.0 and UNIF) but PRG RAM is completely per-mapper. As a result, the NES 2.0 PRG RAM size fields do nothing unless a mapper is specifically set up to check them (and currently very few of them are).