I know that these two mappers are supposed to be the easiest to implement, but i ran into some fundamental problems with them.
First. The game is supposed to write data on a register on the cart to swap data (prg and chr rom respectively to mapper 2 and 3). The problem is that some games tries to write impossible values to those registers so i get a bank number that doesn't exist. For example, ghostBuster (mapper2) writes $FF to the cart, so it is trying to tell me to swap the 255th bank of prg rom into place, witch is impossible. I am supposed to take only part of $FF? I am doing this all wrong?
My second problem is related to all 0kb chr rom. What should I do with them? All mapper 2 games dont have any chr rom, so i just wait until the game feed some data to vram but it seems that it never happens. Maybe its my ppu then, but all other games seems to run fine (well, most of the game...).