What's in the ROM header?

Discussion in 'GBA - Game Development, ROM Hacks and Translations' started by osimonbinladen, Jan 4, 2011.

  1. osimonbinladen
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    osimonbinladen Advanced Member

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    Dec 26, 2008
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    I have found this:
    http://members.iinet.net.au/~freeaxs/gbacomp/#GBA Header

    But what it doesn't explain is how the first 4 bytes work.
    It says it's a "32 bit ARM B Jump to start of ROM executable".
    Can anyone explain where it jumps to in order to boot the ROM?
     
  2. FAST6191

    FAST6191 Techromancer

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    Nov 21, 2005
    http://gbatemp.net/index.php?showtopic=39979&hl=
    From that thread
    http://img141.imageshack.us/img141/6633/id...eginninguy2.png (specifically http://gbatemp.net/t39979-trainer-making-i...st&p=513564 )

    Another link http://nocash.emubase.de/gbatek.htm#gbacartridgeheader

    It is the assembled version of a jump opcode (B is the shortened form of the Branch instruction- ARM means it uses ARM rather than THUMB). http://nocash.emubase.de/gbatek.htm#arminstructionset for more on that.

    By and large the most interesting thing you can do with it is described in the picture above. I have another version of it in the rom hacking docs proper http://www.4shared.com/file/vAdvwFZU/Copy_...m_hacking2.html if you needed one.
     
  3. osimonbinladen
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    osimonbinladen Advanced Member

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    Thanks that's awesome as.
    It was exactly what I was looking for. [​IMG]