The
wiki page for this mapper describes it as one register at address $4100 (the game writes to $4120). That indeed is all there is to it for the later (72-pin?) version of the game
Jovial Race (headerless CRC32: 5AEFBC94). The early 60-pin version of the game (headerless CRC32: A923E441) is different however. It does have the $4120 write as the later version and so can be emulated as mapper 133, the actual cartridge however does not respond to writes at that address. Instead, it has a chip labelled "AX-24G" which responds at addresses $8000/$8001:
After doing the usual write to $4120, the game proceeds with the following write sequence:
Code: Select all
PRG: 32 KiB PRG bank number
CHR: 8 KiB CHR bank number
val = CHR | (((CHR & 1) << 4) ^ 0x10) | ((CHR & 2) << 2) | (PRG << 2);
write(0x8000, 0x01); write(0x8001, val);
write(0x8000, 0x04); write(0x8001, val);
write(0x8000, 0x21); write(0x8001, val);
write(0x8000, 0x24); write(0x8001, val);
These strange $8000 register numbers remind me of the
Toy Story mapper 219, although the numbers are not the same. The original Joy Van release of
Master Chu and the Drunkard Hu (盜帥, Dàoshuài ) has the
same chip. The only known dump of that release is a mapper 3 hack, but even that one retains the same $8000/$8001 writes. The attached Kazzo dumping script, which worked well with that early
Jovial Race cart, should produce a working dump of Dàoshuài as well. The AX-24 chip seems to switch too slowly for the Kazzo, so a delay loop was necessary to get a usable dump.