I'm trying to expand a MMC3 game, and this is what I do :
1) count the number of 16kB PRG bank in the iNES header;
2) increment this number
3) copy the last 16kB PRG bank, and insert it at the offset (nbPRGBank*16*$400) + $10 (iNESHeader).
As the mapper used the two last 8kB PRG bank as fixed, I though my modification would be harmless, but it seems it isn't :s
Does someone knows what is going wrong with my expansion method?
--Edit : more information
Before the mod, the fourth byte into the iNES header was 8. Which means there was 8kB PRG banks. Thus, the PRG went from 0x0010 to 0x2000F.
After the mod, the fourth byte is 9. I made a byte copy from 0x1C010 to 0x2000F and I inserted it at 0x20010, increasing the size of my file of 16kB
1) count the number of 16kB PRG bank in the iNES header;
2) increment this number
3) copy the last 16kB PRG bank, and insert it at the offset (nbPRGBank*16*$400) + $10 (iNESHeader).
As the mapper used the two last 8kB PRG bank as fixed, I though my modification would be harmless, but it seems it isn't :s
Does someone knows what is going wrong with my expansion method?
--Edit : more information
Before the mod, the fourth byte into the iNES header was 8. Which means there was 8kB PRG banks. Thus, the PRG went from 0x0010 to 0x2000F.
After the mod, the fourth byte is 9. I made a byte copy from 0x1C010 to 0x2000F and I inserted it at 0x20010, increasing the size of my file of 16kB