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Gameboy Color Boot ROM Dumped After 10 Years

Posted by Soulskill on from the what's-a-decade-among-friends dept.

An anonymous reader writes "Costis was able to dump the elusive boot ROM from the Gameboy Color by using various voltage and clock glitching tricks. The boot ROM is what initializes the Gameboy hardware, displays the 'GAMEBOY' logo and animation, and makes the trademarked 'cling!' sound effect. Even decapping the CPU had failed previously, but now the boot image and specifics on how it was dumped (along with many photos) are available for download."

3 of 124 comments (clear)

  1. Cool by dintech · · Score: 5, Interesting

    I really love reading about the lengths enthusiasts go to when trying to do this kind of thing. For some reason I had assumed that this had been done already since there is already emulation for gameboy color, right? Can someone explain the significance of this development?

    1. Re:Cool by byuu · · Score: 5, Interesting

      It happens the same with the GBA. While you can emulate games for the GBA without the need for a BIOS file, if you have one, they'll run better \ more accurately (or in some cases, they run instead of not running).

      It really just displays the logo and validates that the Nintendo copyrighted startup logo is present in the ROM. It was a trick to try and prevent third-party publishers from making their own releases. As soon as the Game Boy cartridge is started, the boot ROM is locked out completely and no longer needed. The GBA BIOS is quite different, it has tons of functions like various decompression routines, and without it you tend to have far less accurate timing and you may miss potential edge cases. Think of it as low-level emulation with the BIOS, and high-level emulation (in the vain of N64 graphics emulation) without it.

  2. Very short summary of how ROM was dumped by noidentity · · Score: 5, Interesting

    Here's my summary of how he did it, since the linked blog posting is quite long:

    When the Game Boy Color powers up, a small internal boot ROM is enabled inside the CPU. This displays the logo, verifies that the game ROM is "genuine", then starts executing it. Just before it starts executing user code, it disables the boot ROM by writing to an I/O register. Once disabled, there is no way to re-enable it, thus user code can't easily read the ROM.

    Costis found that if he stopped the CPU clock for a few seconds, then restarted it, many of the CPU registers (including the program counter) would take on random values. So he placed NOP instructions in all external memory, along with a small dump routine, then stopped and restarted the clock just before the boot ROM wrote to the I/O location to disable itself. This caused the program counter to take on a value outside the boot ROM, and execute all the NOPs until it hit his small dump routine.