I tried to modify this ARM assembly program (see bottom of the page) to use subroutines. It should display a red screen on the GBA (and compiling the example program it actually does, so it's not a toolchain use problem), but, when I run it, the screen goes black instead. I'm using devkitARM 30
.arm
.text
.global main
main:
mov r0, #0x4000000
mov r1, #0x400
add r1, r1, #3
str r1, [r0]
mov r0, #0x6000000
stmdb sp!, {r0, r2, lr} @push registers before calling
mov r0, #0xff
mov r1, #0
mov r2, #0
bl set_rgb
mov r1, r0
ldmdb sp!, {r0, r2, lr} @restore registers
mov r2, #0x9600
loop1:
strh r1, [r0], #2
subs r2, r2, #1
bne loop1
infin:
b infin
set_rgb:
@r0: R; r1: G; r2: B; r0: RGB
@truncate everything but the least significant five bits
and r0, r0, #0x1f
and r1, r1, #0x1f
and r2, r2, #0x1f
@form the color
orr r0, r0, r1, lsl #5
orr r0, r0, r2, lsl #10
mov pc, lr @return
The question is, what's wrong in this program?