掌機 - Game Boy Advance - Assembly - BG Mode 3(bitmap)

參考資訊：
https://devkitpro.org/index.php
https://wii.leseratte10.de/devkitPro/
https://patater.com/gbaguy/gbaasm.htm
http://www.coranac.com/tonc/text/toc.htm
https://github.com/devkitPro/devkitarm-crtls
https://gist.github.com/JShorthouse/bfe49cdfad126e9163d9cb30fd3bf3c2

BG Mode 3支援bitmap(每一個像素點的顏色，由使用者指定)，固定使用BG2CNT


每一個像素點的顏色由2Bytes表示


像素填充的起始位址是0x6000000


BG Mode對應的解析度


main.s

    .equ DISPCNT, 0x4000000
    .equ BG2CNT,  0x400000c
    .equ VRAM,    0x6000000

    .global main
     
    .arm
    .text
main:
    ldr r0, =DISPCNT
    ldr r1, =0x403
    str r1, [r0]

    ldr r0, =BG2CNT
    ldr r1, =0x0000
    str r1, [r0]

    ldr r0, =VRAM
    ldr r1, =0x001f
    ldr r2, =(240 * 160)
1:
    strh r1, [r0], #2
    subs r2, r2, #1
    bne 1b
2:
    b 2b

完成