Altered GBA BIOS... ?

Discussion in 'GBA - Emulation' started by Rydian, Mar 10, 2013.

  1. Rydian

    Rydian Resident Furvertâ„¢

    Feb 4, 2010
    United States
    Cave Entrance, Watching Cyan Write Letters
    So some things still need the GBA BIOS because they need access to the built-in functions. Other things made their own versions of these functions and don't need the BIOS (VBA being the prime example). Until now I thought it was an easy split (use the BIOS for things that need it, other things made thiers internal). Then I, somehow, picked up a gba_bios.bin that... was not quite right.

    I ended up putting it in a gPSP test for the PSP without knowing it was an altered file (since it had the same name and properties-size and junk), and gpSP told me on boot that it might not work right since it's been altered. I immediately thought "Oh, I corrupted this file somehow", until the intro played. And it appeared to play fine, but it did not sound normal.

    In addition, booting from that BIOS causes some minor graphics corruption in the "Press A to Continue" screen on the Mother 3 translation... though it appeared to go in-game fine. Switching back to the known-good BIOS fixed both of these differences.

    So was there some project I was never aware of to make a totally reverse-engineered BIOS that multiple systems could use (thus a separate binary instead of making it internal), and they used a different startup sound just in case or something? Or is this the standard BIOS somebody modified for giggles?

    Just in case it really is an altered Nintendo BIOS, no upload, hash instead.
    There's differences from the first byte to the last, even the non-padded size. Legit ends at 0x3F01, altered(?) ends at 0x3F5C, slightly larger.

  2. TyBlood13

    TyBlood13 Weeaboo Trash

    Jul 1, 2012
    United States
    I did like the sound it made, but why bother?
    Emulators let you skip the logo screen anyway, so why make it sound better?
  3. KingBlank

    KingBlank King of Nothing

    Sep 17, 2008
    New Zealand
    New Zealand
    That could be fun, You could try mess around with the data and see if anything else changes!
  4. FAST6191

    FAST6191 Techromancer

    pip Reporter
    Nov 21, 2005
    United Kingdom
    The only official alterations were the DS has a single byte changed (a meaningless one at that- ) and whatever they did for Chinese (ique) ones which is probably nothing for the GBA.

    I vaguely recall a few projects for BIOS function recreation back when but emulators (VBA and no$gba - forks of the former aside there was basically nothing else that mattered until handhelds got powerful enough to emulate it) ultimately did well enough with their internal emulation which rendered most of those moot.
  5. LuigiBlood

    LuigiBlood SNES and 64DD Savior

    Jun 23, 2009
    I mostly hear about that this is a Debug BIOS. Possibly old.