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Utility Sonic & Knuckles Lock-On ROM Maker

Discussion in 'Engineering & Reverse Engineering' started by Devon, Jan 28, 2024.

  1. Devon

    Devon

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    This tool simulates a Sega Genesis game being locked onto Sonic & Knuckles by combining their ROMs similar to how it would be done on a real Sonic & Knuckles cartridge. To get Knuckles in Sonic 2, you will also need the Knuckles in Sonic 2 UPMEM ROM, which will only be applied if a Sonic 2 serial number is found in the locked-on cartridge ROM (unless you set the option to force it to be applied).

    Do note that this isn't a 100% simulation of how the lock-on actually works. That involves a mapper which can enable and disable SRAM and the Knuckles in Sonic 2 UPMEM ROM on the fly, which can't be totally simulated by just combining ROMs. This is merely designed to be a quick and easy way to mimic the lock-on by creating a combined ROM that you can run in any Sega Genesis emulator.

    Luckily, with the Knuckles in Sonic 2 UPMEM, that only really gets run when a cartridge with a Sonic 2 serial number is locked on, and doesn't get turned off. With SRAM, I've added an option to inherit the SRAM settings from the locked-on ROM's header, so that it can be detected properly (though, Sonic 3 & Knuckles is usually checked by emulators, so you shouldn't need to inherit Sonic 3's SRAM settings). That setting is only any useful if you use an exploit to start executing the locked-on cartridge's code and manage SRAM from there.

    Feel free to send in bug reports or feature requests here.
     
    Last edited: Jan 28, 2024
  2. I put the roms in, and I'm clicking the lock-on button. Nothing's happening. What's going on?
     
  3. Devon

    Devon

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    Which ROMs? Are there any error/warning messages that show up?
     
  4. A rom of S&K and VadaPega's S&K-compatible Gatoslip rom.
     
  5. Devon

    Devon

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    That ROM uses the Knuckles in Sonic 2 entry point exploit, which unfortunately is outside the scope of this tool, because that requires the Knuckles in Sonic 2 UPMEM ROM to be able to be toggled on and off. Even then, when you load the ROMs, there's a warning message that will show up that mentions that the ROM has a Sonic 2 serial number, and thus, requires the Knuckles in Sonic 2 UPMEM ROM. In the future, I'll probably add an option to be able to ignore the UPMEM, though.
     
  6. PsychoSk8r

    PsychoSk8r

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    I remember back in the day using “copy /b sk.bin+s3.bin s3k.bin” to lock on =P

    Doesn’t account for any intricacies though. :)
     
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  7. Overlord

    Overlord

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    Must agree, this exact command did immediately come into my head when I saw the first post =D
     
  8. Devon

    Devon

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    And that's fine for ROMs that are 2 MiB or less in size, but not so much for ROMs that are larger than that, which require a different mapping ;)