..

main.s

.arm
.align
.global initSystem
.global main

.mdata:
  @ 4bytes *8
  .word 0x4430
  .word 0x4430
  .word 0x4430
  .word 0x0800
  .align 
.music:
  .word .mdata
initSystem:
    bx lr

main:
    mov r0,#0x04000000      @ I/O space offset
    mov r1,#0x3             @ Both screens on
    mov r2,#0x00020000      @ Framebuffer mode
    mov r3,#0x80            @ VRAM bank A enabled, LCD - bit 8 on 
   
    str r1,[r0, #0x304]     @ Set POWERCNT  # couldn't find reference to this in gbatek
    str r2,[r0]             @     DISPCNT   #
    str r3,[r0, #0x240]     @     VRAMCNT_A #


    ldr r10,=0x04000410      @channel 1 sound
    mov r11,#0x00000032      @vol 50
    str r11,[r10]
    ldr r11, .music          @ address of .mdata

    ldr r12,=0x04000414      @channel 1 data source register
    str r11,[r12]
    ldr r12,=0x04000418      @channel 1 timer register
    mov r11,#0x00000200      @ dunno - data for timer value???
    str r11,[r12]
    ldr r12,=0x0400041A      @channel 1 loopstart register
    mov r11,#0x00000001      @ loop start position
    str r11,[r12]
    ldr r12,=0x0400041C      @channel 1 length register
    mov r11,#0x00000008      @ mdata length N * 4 bytes
    str r11,[r12]
    
    @Bit0-6   Master Volume       (0..127=silent..loud)
    @Bit7     Not used            (always zero)
    @Bit8-9   Left Output from    (0=Left Mixer, 1=Ch1, 2=Ch3, 3=Ch1+Ch3)
    @Bit10-11 Right Output from   (0=Right Mixer, 1=Ch1, 2=Ch3, 3=Ch1+Ch3)
    @Bit12    Output Ch1 to Mixer (0=Yes, 1=No) (both Left/Right)
    @Bit13    Output Ch3 to Mixer (0=Yes, 1=No) (both Left/Right)
    @Bit14    Not used            (always zero)
    @Bit15    Master Enable       (0=Disable, 1=Enable)
    @Bit16-31 Not used            (always zero)
    ldr r12,=0x04000500      @ sound control register

    ldr r11,=0x0000B032      @ master vol at 50 - master enable
    str r11,[r12]
    mov r11,#0x00000032      @ master vol at 50
    str r11,[r12]
   
    @Bit0-6    Volume Mul   (0..127=silent..loud)
    @Bit7      Not used     (always zero)
    @Bit8-9    Volume Div   (0=Normal, 1=Div2, 2=Div4, 3=Div16)
    @Bit10-14  Not used     (always zero)
    @Bit15     Hold         (0=Normal, 1=Hold last sample after one-shot sound)
    @Bit16-22  Panning      (0..127=left..right) (64=half volume on both speakers)
    @Bit23     Not used     (always zero)
    @Bit24-26  Wave Duty    (0..7) ;HIGH=(N+1)*12.5%, LOW=(7-N)*12.5% (PSG only)
    @Bit27-28  Repeat Mode  (0=Manual, 1=Loop Infinite, 2=One-Shot, 3=Prohibited)
    @Bit29-30  Format       (0=PCM8, 1=PCM16, 2=IMA-ADPCM, 3=PSG/Noise)
    @Bit31     Start/Status (0=Stop, 1=Start/Busy)
    
    @ vol 50 => 0x32
    
    @ desmune lcd seems to be 512 pixels across (contrary to wiki specifying 256)
    @#262144                @ color to use 18bit max
    mov r6, #32             @ Color change delay
    mov r7, #262144         @ color to start with
    mov r8, #0x16000         @ number of pixels of the screen occupied by animation
    mov r9, #0x08           @ color delta 
    mov r1, r7              @ Writing pixel

event: mov r4, #512       @ number of frames 512=0x200
    mov r2, r8              @ number of pxels for lp loop
    mov r3, r6              @ r3 is how often to change color 

nf:    
    mov r0,  #0x06800000      @ VRAM offset #reset each loop
lp: 
    strh r1, [r0], #1       @ Write r1 into in and increment r0 by 1
    subs r2, r2, #1         @ decrement number of pixels to write
    bne lp                  @ branch if not equal (is it checking the flags??)
    mov r2, r8              @ resest number of pixel counter

    @@ Delay r6 / r3
    @@ Between color change
    subs r3,   r3, #4        @ if color change delay reaches zero then change color
    bne after
next_color:
    mov r3, r6               @ reset the color change amount 
    sub r1, r1, r9           @ modify color by color change amount
after:
    subs r4, r4, #1          @ number of loops
    bne nf                   @ branch on zero back to r4
    
    b event

inf: b inf

@ blue gradient
@    mov r0, #0x06800000     @ VRAM offset
@    mov r1, #0x00          @ Writing pixel value
@    mov r2, #0x18000         @ number of pxels
@    mov r3, #0x800
@lp: strh r1, [r0], #1      @ Write a pixel in - increment r0 by #128
@    subs r3,r3, #1
@    bne next_px
@next_color: adds  r1, r1, #
@    mov r3, #0x800
@next_px   : subs r2,   r2, #1          @ decrement r2 - update flags
@    bne lp                  @ branch if not equal (is it checking the flags??)

@white lemon blue
@    mov r0, #0x06800000     @ VRAM offset
@    mov r1, #0x00          @ Writing pixel value
@    mov r2, #0x18000         @ number of pxels
@    mov r3, #0x1600
@lp: strh r1, [r0], #1      @ Write a pixel in - increment r0 by #128
@    subs r3,r3, #1
@    bne next_px
@next_color: adds  r1, r1, #0xffffffff
@    mov r3, #0x1600
@next_px   : subs r2,   r2, #1          @ decrement r2 - update flags
@    bne lp                  @ branch if not equal (is it checking the flags??)
@
@nf: b nf                    @ Sit in an infinite loop to finish