Megadrive Rom Hacking: Ledgend of Wukong

These are the conclusions from Eke-Eke when he got another dump from another guy by when he implemented support to Legend of Wukong into GenPlusGX:

 "1) your dump is actually overdumped and should only be 2228224 bytes
 (range is $000000-$21FFFF, just as indicated in ROM header), the game
 uses a custom checksum routine that covers this area, which means the
 data you dumped is correct since the test passes in any emu.

 2) 8K of SRAM is mapped between $3C0001 and $3C3FFF (odd address only)
 and is tested on startup (the game writes data in this area and expect
 same data to be read)

 3) Bytes written to low ROM area (the game writes address $E01 but maybe
 other addresses work) goes to cartridge custom bank-switching hardware:
 - when bit 7 is set (0x80 for example), $200000-$21FFFF (last 128k ROM
 bank) is remapped to $000000- $01FFFF (first 128k ROM bank).
 - when bit 7 is cleared (0x00 for example), $200000-$21FFFF is mapped
 normally.

 I've yet to figure a patched ROM that could work in any emulator and
 flashcarts as they are actually two things to fix:

 (1) many emulators (like Kega I think) and flashcarts only support SRAM
 mapped at $200000-$20FFFF. I don't think this is fixable since it would
 require too many modifications to the code to change the SRAM access
 routines so the only solution  would be to use flashcarts or emulators
 that properly use info from the ROM header and support SRAM mapped to
 any address (Regen apparently does since it does not give me a SRAM
 error with this ROM), will try Everdrive when I have the time

 (2) once $E01 has been written to trigger bank-switching, all memory
 access, jump, etc... to $200000-$21FFFF should be patched to use
 $000000- $01FFFF instead. The problem is that it can be complicated to
 find all locations in code where absolute addresses need to be patched.

 And here are the patches to the game work in any emulator:

 000414:4E71
 000416:4E71 ; bypass SRAM check on startup (only needed for emulators, like Fusion, or flashcarts that do not support SRAM to be mapped in unusual region like $3c000-$3c3fff)

 20777A:4E71 ; bypass checksum routine

 007730:000F
 0FE17E:0000
 0FFF20:000F
 0FFF2E:000F
 01C5BC:0010
 007596:0010
 0FFF8C:0010 ; bypass ROM bank-switching (maybe there are more ?)"