Introduction

The Gameboy Advance (GBA) sound system may seem to many as black magic because of the availability of information on this specific part of the machine is near inexistent. Moreover, finding relevant or accurate specs for the older Gameboy was and is still problematic. The result is that many will take little or no advantages of sound in their projects. This site will attempt to fill this gap, by providing an *Unofficial*, comprehensive and (well, as much as possible in the circumstances) accurate specification of the GBA sound system (GBAS). It is assumed that the reader will have some knowledge of the other basic functionalities of the GBA and knows how to program in C.

The GBAS is a big step forward its older brothers because it now includes two Pulse Width Modulators (PWM) that act as digital-to-analog converters. This adds to the 4 sound channels present on the previous Gameboys. One important improvement to the sound system is that channel 3 's wave ram is now banked, allowing for distortion-free dynamic wave ram reloading.

The GBA BIOS also contains many sound-related functions, for converting MIDI notes and playing music. BIOS may be covered in the future.

 The registers

Sound registers, as for all other registers in the GBA, are memory mapped and they span from 0x0400060 to 0x40000A6.

Address Name Function
0x04000060 REG_SOUND1CNT_L Sound 1 Sweep control
0x04000062 REG_SOUND1CNT_H Sound 1 Lenght, wave duty and envelope control
0x04000064 REG_SOUND1CNT_X Sound 1 Frequency, reset and loop control
0x04000068 REG_SOUND2CNT_L Sound 2 Lenght, wave duty and envelope control
0x0400006C REG_SOUND2CNT_H Sound 2 Frequency, reset and loop control
0x04000070 REG_SOUND3CNT_L Sound 3 Enable and wave ram bank control
0x04000072 REG_SOUND3CNT_H Sound 3 Sound lenght and output level control
0x04000074 REG_SOUND3CNT_X Sound 3 Frequency, reset and loop control
0x04000078 REG_SOUND4CNT_L Sound 4 Lenght, output level and envelope control
0x0400007C REG_SOUND4CNT_H Sound 4 Noise parameters, reset and loop control
0x04000080 REG_SOUNDCNT_L Sound 1-4 Output level and Stereo control
0x04000082 REG_SOUNDCNT_H Direct Sound control and Sound 1-4 output ratio
0x04000084 REG_SOUNDCNT_X Master sound enable and Sound 1-4 play status
0x04000088 REG_SOUNDBIAS Sound bias and Amplitude resolution control
0x04000090 REG_WAVE_RAM0_L Sound 3 samples 0-3
0x04000092 REG_WAVE_RAM0_H Sound 3 samples 4-7
0x04000094 REG_WAVE_RAM1_L Sound 3 samples 8-11
0x04000096 REG_WAVE_RAM1_H Sound 3 samples 12-15
0x04000098 REG_WAVE_RAM2_L Sound 3 samples 16-19
0x0400009A REG_WAVE_RAM2_H Sound 3 samples 20-23
0x0400009C REG_WAVE_RAM3_L Sound 3 samples 23-27
0x0400009E REG_WAVE_RAM3_H Sound 3 samples 28-31
0x040000A0 REG_FIFO_A_L Direct Sound channel A samples 0-1
0x040000A2 REG_FIFO_A_H Direct Sound channel A samples 2-3
0x040000A4 REG_FIFO_B_L Direct Sound channel B samples 0-1
0x040000A6 REG_FIFO_B_H Direct Sound channel B samples 2-3

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