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Format of MSXAdvance (v1) GBA images:
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???? bytes:  MSXAdvance.gba contents
(optional) 76800 bytes:  Splash screen (raw 240x160 15bit image)
----
4 bytes:  Identifier = "MSX",0x1A
4 bytes:  ROM size
2 bytes:  ROM flags
1 byte:   Branch hacks, bit 0-3: opcode, bit 4-7: length. (not yet).
1 byte:   Reserved (set to 0)
4 bytes:  Autoscroll value (a.k.a. "sprite following")
1 byte:   BIOS flag, bit0=1 for BIOS rom.
15 bytes: Reserved (set to 0)
32 bytes: ROM title (NULL terminated)
???? bytes:  ROM contents (.MSX format)
----
4 bytes:  Next ROM indentifier
etc etc...
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ROM flags:
    Bit 0: Reserved
    Bit 1: Reserved
    Bit 2: Reserved
    Bit 3: Reserved
    Bit 4: Enable CPU speed hack
           (Enables the branch hacks)
    Bit 5: 0=Autoscroll value is a sprite number
           1=Autoscroll value is a memory location
    Everything else:  Reserved (set to 0)


