Convert GBA multiboot game to cartridge format

mb2gba.s

@ Bootstrap for running a GBA multiboot game stored in a ROM cartridge

@ Assemble with:
@ arm-none-eabi-as -o mb2gba.o mb2gba.s
@ arm-none-eabi-objcopy -O binary mb2gba.o mb2gba.bin
@ base64 mb2gba.bin

start:
    @ Copy the game into ram
    mov r0, #0x04000000
    adr r1, rom
    str r1, [r0, #0xd4]  @ DMA3SAD
    mov r1, #0x02000000
    str r1, [r0, #0xd8]  @ DMA3DAD
    mov r1, #0x84000000  @ Transfer type = 32bit, size = 0x10000 * 4
    str r1, [r0, #0xdc]  @ DMA3CNT

    @ Set reset address to ram
    mov r0, #0x03000000
    add r0, #0x8000
    mov r1, #1
    strb r1, [r0, #-6]

    @ Reset
    swi 0

@ Pad the ROM to at least 0x140 to avoid mGBA's multiboot detection
.org 0x140 - 0xc0 - start, 0
rom:

mb2gba.sh

#!/bin/sh
# Convert a GBA multiboot binary into a GBA ROM, by including a pre-assembled bootstrap
# This can be used to play multiboot games using a flash cartridge.

# Example usage:
# ./mb2gba.sh < game.mb > game.gba

# Back up game header from the multiboot rom
header="$(dd bs=1 count=192 | base64)"

# Set the start address to 0x080000c0
echo LgAA6g== | base64 -d

# Copy the rest of the header from the multiboot rom
echo "$header" | base64 -d | dd bs=1 skip=4

# Add the bootstrap binary with padding up to 0x140
echo AQOg43QQj+LUEIDlAhSg49gQgOUhE6Dj3BCA5QMEoOMCCYDiARCg4wYQQOUAAADvAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAAA= | base64 -d

# Append the entire multiboot binary
echo "$header" | base64 -d
dd