MD Port Swap

MD Port Swap — Genesis/Mega Drive Controller Port Swapper

Win32 GUI tool for Sega Genesis / Mega Drive ROMs that:

1. Swaps all Controller Port 1 <-> Port 2 I/O register references in ROM code.
2. Recomputes and fixes the ROM header checksum afterward.

Originally intended for using an external controller as Port 1 on the Sega Nomad, but you can use it however you want

The tool scans the whole ROM for these sequences and flips the last byte (03<->05, 09<->0B), which makes the game read/write the pad through the opposite port everywhere in the code, with no game-logic changes.

This won't help games that use indirect/computed I/O addressing (rare).