Hacking and building the ROM

last updated: Feb 17, 2021

Build Requirements

I’m on Win10/64, so I can’t tell you how to set things up for other OS’es.

• The unpatched ROM that has a matching CRC/checksum (see Readme.md in the repository)
• VASM (vasmm68k_mot_win32.exe) <- Win-compiled by Rob
• supertails66 yuitools srecpatch.exe
• fixheader.exe which fixes the ROM’ internal checksum in the header and prevents red-screen lockups

Prepare filesystem

This may vary between patch repositories, but I will update older releases to use the same structure for convenience. Folders are set up like this:

• Root folder (could be anywhere on your computer)
  • vasmm68k_mot_win32.exe
  • srecpatch-jp.exe
  • fixheader.exe
  • [Folders] contents of repository
    • patch.asm (etc, additional asm files)
    • msu-drv.bin
    • msuLockout.bin
    • .bat files (_make_srec-jp.bat, _apply_srec-jp.bat, build.bat etc.)
    • [Folder] ROMS
      • in.md (unpatched, padded ROM)
    • [Folder] OUTPUT

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ROM Padding

To allow insertion of additional data into the ROM some padding (increase of filesize) is needed. You can use any method for this task, I do it with WindHex32 by opening the ROM, then opening the menu and selecting “Tools -> Increase/Decrease ROM size”. This is convenient as you can select the new size in MBITS

Please refer to the source of patch.asm to find out what size is needed.

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Build

1. Prepare the input ROM in folder /ROMS by adding padding and renaming to in.md
2. Prepare your filesystem as described above
3. Launch .bat files in this order (or simply use build.bat which does the same thing)
   • _make_srec-jp.bat
   • _apply_srec-jp.bat
   • _fixheader.bat
4. Find the patched ROM in OUTPUT/out.md

Other topics

Status Participate Using the Patch Lockout screen Play on Mega Everdrive Pro Play in Emulators Play on MegaSD Play on real console and CD Troubleshooting CD Audio Tracks Creating Music from VGM Hacking and building the ROM