ARM programming for Gameboy Advance

Technical Resources

GBATEK - complete documentation on the GBA and NDS

ARM Hello World Series

Hello World on the GameBoy Advance - ARM Assembly Lesson H2

Hello World on the GameBoy Advance with ARM Thumb Assembly - Lesson H4 [GBA]

ARM Platform Specific Lessons

Lesson P2 - Bitmap graphics and Palette definitions on GameBoy Advance (16 bit - 32768 colors) [GBA]

Lesson P3 - Bitmap graphics and Palette definitions on GameBoy Advance (8 bit - 256 colors) [GBA]

Lesson P5 - Joypad & Pen on the GBA / NDS ... Key reading on Risc OS [NDS] [GBA] [ROS]

Lesson P6 - Sound on the Gameboy Advance [GBA]

Lesson P8 - 16 color Tilemap on the Gameboy Advance and Nintendo DS! [GBA] [NDS]

Lesson P9 - Hardware Sprites on the Gameboy Advance and Nintendo DS! [GBA] [NDS]

ARM Simple Samples

Moving a sprite on RiscOS - Simple ARM Assembly Lesson S1

Sprite moving on the GameBoy Advance - Arm Assembly Lesson S2

Lesson S4 - Sprite moving on the GameBoy Advance (Thumb) [GBA]

Screen Display

In these tutorials we're going to use mode 4 - this effectively has 2 bitmap layers of 256 colors each, they are NOT PLANAR - they are linear bitmap format.
Note, it is not possible to write in bytes to the screen, We must write in WORDS... if we write a byte, both bytes of the word will be set the same - effectively halving the horizontal resolution

In 16 bit bitmap modes the color bits are in the format %-BBBBBGGGGGRRRRR

Memory Map

Sound

Port	Name	Description	Bits	Details
0x4000060	SOUND1CNT_L	Channel 1 Sweep register	---------TTTDSSS	S=sweep shift D=direction T=Time
0x4000062	SOUND1CNT_H	Channel 1 Duty/Length/Envelope (NR11	VVVVDSSSWWLLLLLL	L=length W=wave pattern duty S=envelope Step D= env direction V=Volume
0x4000064	SOUND1CNT_X	Channel 1 Frequency/Control	IL---FFFFFFFFFFF	I=Init sound L=no loop F=Frequency
0x4000068	SOUND2CNT_L	Channel 2 Duty/Length/Envelope (NR21	VVVVDSSSWWLLLLLL	L=length W=wave pattern duty S=envelope Step D= env direction V=Volume
0x400006C	SOUND2CNT_H	Channel 2 Frequency/Control	IL---FFFFFFFFFFF	I=Init sound L=no loop F=Frequency
0x4000070	SOUND3CNT_L	Channel 3 Stop/Wave RAM select (NR30)	-------PBD-----	D=Dimension B=Bank P=Play (1=on 0=off)
0x4000072	SOUND3CNT_H	Channel 3 Length/Volume	FVV-----LLLLLLLL	L=sound Length V=volume F=Force
0x4000074	SOUND3CNT_X	Channel 3 Frequency/Control	IL---FFFFFFFFFFF	I=Init sound L=no loop F=Frequency
0x4000078	SOUND4CNT_L	Channel 4 Length/Envelope	VVVVDSSS--LLLLLL	L=length S=envelope Step D= env direction V=Volume
0x400007C	SOUND4CNT_H	Channel 4 Frequency/Control	IL------SSSSCRRR	R=dividing Ration, C=Counter S=shify clock freq L+no Loop I=Init sound
0x4000080	SOUNDCNT_L	Control Stereo/Volume/Enable	LLLLRRRR-lll-rrr	LR=Channel on lr=master vol(7=max)
0x4000082	SOUNDCNT_H	Control Mixing/DMA Control	BBBBAAAA-ba-VV
0x4000084	SOUNDCNT_X	Control Sound on/off	M---4321	M=Master ON 1234 (Read) = Sound on flag
0x4000088	BIOS SOUNDBIAS	Sound PWM Control	AA----BBBBBBBBB-	A=Amplitude B=Bios
0x4000090	WAVE_RAM	16 Bytes	1111222233334444	4 bit sample data
0x40000A0	FIFO_A	Channel A FIFO	----DDDD----DDDD	D=Wawave Data
0x40000A4	FIFO_B	Channel B FIFO	----DDDD----DDDD	D=Wawave Data

Ports

Joypad

Reading in the GBA buttons is super easy!... just read in from address  0x4000130... you'll get a word back with all the keys in the format %------LRDULRSsBA

In Tilemap mode, Sprite patterns are defined by by VRAM addresses 0x06010000+

In Bitmap mode, Sprite patterns are defined by by VRAM addresses 0x06014000+, Due to the size of the bitmap screen ram, only tile numbers 512+ are usable

Sprites use the 256 colors in the OBJ palette from address 0x05000200+

Sprites are made up of 8x8 patterns with either 16 colors (4bpp) or 256 colors (8bpp) defined by the color bit in the first parameter.

Sprite XY pos 0,0 is the top left corner of the screen.

H Byte

L Byte

VRAM Address

F

E

D

C

B

A

9

8

7

6

5

4

3

2

1

0

Details

7000000h

S

S

C

M

T

T

D

R

Y

Y

Y

Y

Y

Y

Y

Y

Y=Ypos S=Shape (Square /HRect / Vrect) C=Colors(16/256) M=Mosiac T=Transparent D=Disable/Doublesize R=Rotation

7000002h

S

S

V

H

R

R

R

X

X

X

X

X

X

X

X

X

X=Xpos S=Obj Size (8x8,16x16,32x32,64x64) VH=V/HFlip R=Rotation parameter

7000004h

C

C

C

C

P

P

T

T

T

T

T

T

T

T

T

T

T=Tile Number C=Color palette (16 color mode) P=Priority

7000006h

Unused by sprite

Rotation and Scaling

On the GBA and NDS In some modes, Layers BG2 and BG3 can be rotated and scaled. The control of this is performed by registers 4001020h-400103Ch For the mathematically challenged (Like me) I've created a spreadsheet which helps calculate the correct values for the effect you want... get it Here

NDS Example:

Learn Assembly for the Greatest Classic Processors:  Z80 - 6502 - 68000 - 8086 - ARM