INES Mapper 025

iNES Mapper 025 is used to represent the VRC4b (PCB 351406) and VRC4d (PCB 352400) variants of Konami's VRC4 mapper, as well as the VRC2-using board 351948 used for Ganbare Goemon Gaiden: Keita Ougon Kiseru. The last has 8kB RAM (like VRC4) and doesn't divide the CHR bank numbers by two (unlike mapper 22).

For details see the following:

• INES Mapper 021 / VRC4
• INES Mapper 022 / VRC2

Note that the VRC4d variant uses different address lines to select registers than 351948 and the VRC4b variants. Your emulator implementation must either combine address lines (like FCEUX; bitwise OR is good enough), use checksums, or NES 2.0 submappers.