0xrsydn/gameboy-rust
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feat(audio): implement PSG noise channel 4

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0xrsydn 2026-10-07 02:51:46 +07:00
commit 8ae7b3cf72
14 changed files with 774 additions and 75 deletions
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26
crates/gba-core/src/audio.rs
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@ -1,7 +1,9 @@
//! Nominal Direct Sound and PSG pulse channels 1–2. No host audio output.
//! Nominal Direct Sound, PSG pulse channels 1–2, and noise channel 4. No host audio output.
mod modulation;
mod noise;
mod pulse;
use noise::Noise;
use pulse::Pulse;
const SEQUENCER_PERIOD: u32 = 32768; // 16,777,216 Hz / 512 Hz.
@ -80,6 +82,7 @@ pub(crate) struct Audio {
enabled: bool,
psg: [u16; 17],
pulses: [Pulse; 2],
noise: Noise,
sequencer_phase: u16,
next_step: u8,
control: u16,
@ -100,7 +103,7 @@ impl Audio {
{
return Some("reserved PSG volume selection");
}
if self.enabled && matches!(address, 0x0400_0075 | 0x0400_007d) && value & 0x80 != 0 {
if self.enabled && address == 0x0400_0075 && value & 0x80 != 0 {
Some("PSG channel trigger (synthesis not implemented)")
} else {
None
@ -123,6 +126,9 @@ impl Audio {
}
pub(crate) fn read8(&self, address: u32) -> Option<u8> {
if (0x0400_0078..=0x0400_007d).contains(&address) {
return Some(self.noise.read(address - 0x0400_0078));
}
if let Some((index, offset)) = Self::pulse_register(address) {
return Some(self.pulses[index].read(offset));
}
@ -135,8 +141,6 @@ impl Audio {
0x0400_0074 => 0x4000,
0x0400_0070 => 0x00e0,
0x0400_0072 => 0xe000,
0x0400_0078 => 0xff00,
0x0400_007c => 0x40ff,
0x0400_0080 => 0xff77,
_ => 0,
};
@ -147,6 +151,7 @@ impl Audio {
(u16::from(self.enabled) << 7)
| u16::from(self.pulses[0].modulation.active)
| (u16::from(self.pulses[1].modulation.active) << 1)
| (u16::from(self.noise.modulation.active) << 3)
}
SOUNDBIAS => self.bias,
0x0400_0086 | 0x0400_008a => 0,
@ -173,6 +178,13 @@ impl Audio {
}
continue;
}
if (0x0400_0078..=0x0400_007d).contains(&address) {
if self.enabled {
self.noise
.write(address - 0x0400_0078, value, self.next_step);
}
continue;
}
let shift = (address & 1) * 8;
let merge = |old: u16| (old & !(255 << shift)) | (u16::from(value) << shift);
match address & !1 {
@ -194,6 +206,7 @@ impl Audio {
if self.enabled && value & 0x80 == 0 {
self.psg = [0; 17];
self.pulses = [Pulse::default(); 2];
self.noise = Noise::default();
for fifo in &mut self.fifo {
fifo.reset_queue();
}
@ -222,12 +235,14 @@ impl Audio {
for pulse in &mut self.pulses {
pulse.advance(count);
}
self.noise.advance(count);
let phase = u32::from(self.sequencer_phase) + count;
if phase == SEQUENCER_PERIOD {
self.sequencer_phase = 0;
for pulse in &mut self.pulses {
pulse.clock(self.next_step);
}
self.noise.clock(self.next_step);
self.next_step = (self.next_step + 1) & 7;
} else {
self.sequencer_phase = phase as u16;
@ -278,6 +293,9 @@ impl Audio {
psg_sample += pulse.sample();
}
}
if psg_control & (1 << (11 + side * 4)) != 0 {
psg_sample += self.noise.sample();
}
let volume = ((psg_control >> (side * 4)) & 7) as i16 + 1;
// Sum PSG channels before scaling, so fractional bits are discarded once.
*level += (psg_sample * volume * ratio) >> 2;