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More Experimentation With Sonic & Knuckles Lock-On Technology

  • Hi Everyone,

    A few weeks ago I posted a support request regarding whether the Sonic & Knuckles + Sonic The Hedgehog 3 ROM could be scraped. Thanks to everyone's help on here, I got it all sorted.

    However, I was browsing around the in-game RGUI, with Genesis Plus GX as the loaded core, and found a setting in the Options menu called "Cartridge Lock-On"; one of the choices for this setting was "Sonic & Knuckles". Others were the cheat devices which were available for the Megadrive.

    I did some further research online and found that this option can be used, but that additional files are required to be placed in the BIOS folder.

    The first is sk.bin, which is apparently a copy of the Sonic & Knuckles ROM, but with a different file extension, and placed in a different folder. That one was easy to sort out.

    The other is sk2chip.bin, and that's proving difficult. I have been unable to find that file online, although it is apparently possible to create it by extracting part of the Sonic & Knuckles + Sonic The Hedgehog 2 ROM. I could only find limited information on how to do it, but one article mentioned opening the ROM in a hex editor, jumping to offset 00300000, and copying everything after that point into a new file. Apparently the resulting file should be 256kb.

    I installed a freeware tool called Hex Fiend, as I'm on a Mac. Using this tool, I was able to jump to the given offset. However, the content after that point amounted to far more than 256kb; in fact, it was over 3MB. I'm guessing that I'm doing something wrong. I have no practical knowledge of Hex, and am only exploring it at all to see if I can get the Cartridge Lock-On feature within Genesis Plus GX to work.

    None of this is strictly necessary as I already have working ROMs of the games combined. I just like exploring this type of thing, and it would be awesome to get it working.

    Does anyone have any ideas on what I might need to do, admittedly with very little information? Not sure if I'm allowed to post a screenshot showing my hex editor with the code of a dumped ROM.

    For reference, I am running RetroPie 4.4 on a Pi 3 Model B+.

    Any help appreciated.


  • Global Moderator

    @RetrOkada said in More Experimentation With Sonic & Knuckles Lock-On Technology:



    Remember: your Pi is running a standard Linux distribution, so there's really no need to do this via a graphical hex editor on your Mac.

  • Hi @psyke83, thanks for your reply, and for posting that link.

    I think I came across it before, but wasn't sure what to actually do with that series of commands. I am completely new to Linux; Raspberry Pi/RetroPie is my first exposure to it.

    My understanding is that I need to:

    1. Copy the Sonic & Knuckles + Sonic The Hedgehog 2 (World) ROM to the ROMs directory on my Pi.
    2. Connect a keyboard to my Pi and push F4 to go into the command prompt.
    3. Enter the three commands listed on the page which you linked.

    Am I on the right lines?


  • Global Moderator


    Yes... making sure that you enter the same directory that contains the ROM you transferred. Also, make sure to amend the instructions if your file is named differently.

    Depending on how you've set up your Pi (i.e. if it's connected to your home network), it may be a lot easier for you to connect to your Pi via a SSH client on your Mac to avoid the need of plugging in a keyboard and typing stuff into a terminal on your TV.

    You need to enable SSH on the Pi first. See:

    I've no recent experience with macOS, but the instructions do say that macOS includes the ssh command. I would suggest you follow those instructions.

    On a Linux-based system, you would open a terminal and invoke ssh pi@retropie and then entering the password to get you connected (assuming that you didn't change the Pi's default hostname). I am guessing that macOS's ssh client would be no different.

    Anyway, it's just a suggestion - feel free to ignore SSH and follow the steps directly.

  • Hi @psyke83,

    Thanks very much for your help with that ... worked perfectly:).

    I connected the keyboard directly to my pi and ran the commands that way.

    Really appreciate your help.


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