spsr_usrsys.asm

format binary as 'gba'

gba_header:
        ; Branch to 0x080000C0 (4 bytes)
        dw      0xEA00002E

        ; Nintendo logo (156 bytes)
        db      0x24,0xFF,0xAE,0x51,0x69,0x9A,0xA2,0x21,0x3D,0x84
        db      0x82,0x0A,0x84,0xE4,0x09,0xAD,0x11,0x24,0x8B,0x98
        db      0xC0,0x81,0x7F,0x21,0xA3,0x52,0xBE,0x19,0x93,0x09
        db      0xCE,0x20,0x10,0x46,0x4A,0x4A,0xF8,0x27,0x31,0xEC
        db      0x58,0xC7,0xE8,0x33,0x82,0xE3,0xCE,0xBF,0x85,0xF4
        db      0xDF,0x94,0xCE,0x4B,0x09,0xC1,0x94,0x56,0x8A,0xC0
        db      0x13,0x72,0xA7,0xFC,0x9F,0x84,0x4D,0x73,0xA3,0xCA
        db      0x9A,0x61,0x58,0x97,0xA3,0x27,0xFC,0x03,0x98,0x76
        db      0x23,0x1D,0xC7,0x61,0x03,0x04,0xAE,0x56,0xBF,0x38
        db      0x84,0x00,0x40,0xA7,0x0E,0xFD,0xFF,0x52,0xFE,0x03
        db      0x6F,0x95,0x30,0xF1,0x97,0xFB,0xC0,0x85,0x60,0xD6
        db      0x80,0x25,0xA9,0x63,0xBE,0x03,0x01,0x4E,0x38,0xE2
        db      0xF9,0xA2,0x34,0xFF,0xBB,0x3E,0x03,0x44,0x78,0x00
        db      0x90,0xCB,0x88,0x11,0x3A,0x94,0x65,0xC0,0x7C,0x63
        db      0x87,0xF0,0x3C,0xAF,0xD6,0x25,0xE4,0x8B,0x38,0x0A
        db      0xAC,0x72,0x21,0xD4,0xF8,0x07

        db      'spsr_usrsys', 0   ; Game title (12 bytes)
        db      '0000'             ; Game code (4 bytes)
        db      'AN'               ; Make code (2 bytes)
        db      0x96               ; Fixed (1 byte)
        db      0x00               ; Unit code (1 byte)
        db      0x80               ; Device type (1 byte)
        db      0,0,0,0,0,0,0      ; Unused (7 bytes)
        db      0x00               ; Game version (1 byte)
        db      0xa2               ; Complement (1 byte)
        db      0,0                ; Reserved (2 bytes)

_start:
    ; Reset r2
    mov r2, 0

    ; Setup DISPCNT
    mov r0, 0x00000400
    orr r0, 0x00000004
    mov r1, 0x04000000
    strh r0, [r1]

test1:
    ; Here, CPSR should be equal to 0x4000001f
    ; Copy a value to SPSR
    mov r0, 0xb0000000
    orr r0, 0x00000010
    msr spsr, r0

    ; Compare the value in SPSR with the value in CPSR
    mrs r1, cpsr
    teq r0, r1
    bne test2

    ; The value written to SPSR was (also?) written in CPSR.
    orr r2, 0x001f

test2:
    ; Copy a value to CPSR
    mov r0, 0x70000000
    orr r0, 0x0000001f
    msr cpsr, r0

    ; Check the value in SPSR
    mrs r1, spsr
    teq r0, r1
    bne test3

    ; The value written to CPSR was also written in SPSR.
    orr r2, 0x03e0

test3:
    ; Copy a value to SPSR
    mov r0, 0xc0000000
    orr r0, 0x0000001f
    msr spsr, r0

    ; Go to user mode
    mrs r1, cpsr
    mov r3, 0x80000000
    mov r3, r3, asr 24
    and r1, r3
    orr r1, 0x00000010
    msr cpsr, r1

    ; Load SPSR in user mode
    mrs r1, spsr
    teq r0, r1
    bne displayResult

    ; The SPSR is the same
    orr r2, 0x7c00

displayResult:
    mov r0, 0x05000000
    strh r2, [r0]

halt:
    b halt