0xrsydn/gameboy-rust
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feat(audio): implement PSG pulse channel 2

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0xrsydn 2026-10-07 02:30:16 +07:00
commit aee3621513
15 changed files with 457 additions and 89 deletions
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62
crates/gba-core/src/audio.rs
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@ -1,4 +1,4 @@
//! Nominal Direct Sound and PSG pulse channel 1. No host audio output.
//! Nominal Direct Sound and PSG pulse channels 1–2. No host audio output.
mod pulse;
use pulse::Pulse;
@ -78,7 +78,7 @@ impl Fifo {
pub(crate) struct Audio {
enabled: bool,
psg: [u16; 17],
pulse: Pulse,
pulses: [Pulse; 2],
sequencer_phase: u16,
next_step: u8,
control: u16,
@ -99,10 +99,7 @@ impl Audio {
{
return Some("reserved PSG volume selection");
}
if self.enabled
&& matches!(address, 0x0400_006d | 0x0400_0075 | 0x0400_007d)
&& value & 0x80 != 0
{
if self.enabled && matches!(address, 0x0400_0075 | 0x0400_007d) && value & 0x80 != 0 {
Some("PSG channel trigger (synthesis not implemented)")
} else {
None
@ -113,9 +110,20 @@ impl Audio {
1 ^ usize::from((self.psg[8] >> 6) & 1)
}
/// Channel 2 has no sweep register. Its register gap must not alias any
/// pulse state, particularly the shared engine's sweep configuration.
fn pulse_register(address: u32) -> Option<(usize, u32)> {
match address {
SOUND_START..=0x0400_0065 => Some((0, address - SOUND_START)),
0x0400_0068..=0x0400_0069 => Some((1, address - 0x0400_0066)),
0x0400_006c..=0x0400_006d => Some((1, address - 0x0400_0068)),
_ => None,
}
}
pub(crate) fn read8(&self, address: u32) -> Option<u8> {
if (SOUND_START..=SOUND_START + 5).contains(&address) {
return Some(self.pulse.read(address - SOUND_START));
if let Some((index, offset)) = Self::pulse_register(address) {
return Some(self.pulses[index].read(offset));
}
if (WAVE_RAM..FIFO_A).contains(&address) {
return Some(self.wave[self.wave_bank()][(address - WAVE_RAM) as usize]);
@ -123,9 +131,7 @@ impl Audio {
let value = match address & !1 {
SOUND_START..=0x0400_0080 => {
let mask = match address & !1 {
0x0400_0060 => 0x007f,
0x0400_0062 | 0x0400_0068 => 0xffc0,
0x0400_0064 | 0x0400_006c | 0x0400_0074 => 0x4000,
0x0400_0074 => 0x4000,
0x0400_0070 => 0x00e0,
0x0400_0072 => 0xe000,
0x0400_0078 => 0xff00,
@ -136,7 +142,11 @@ impl Audio {
self.psg[((address - SOUND_START) / 2) as usize] & mask
}
SOUNDCNT_H => self.control,
SOUNDCNT_X => (u16::from(self.enabled) << 7) | u16::from(self.pulse.active),
SOUNDCNT_X => {
(u16::from(self.enabled) << 7)
| u16::from(self.pulses[0].active)
| (u16::from(self.pulses[1].active) << 1)
}
SOUNDBIAS => self.bias,
0x0400_0086 | 0x0400_008a => 0,
_ => return None, // FIFO is write-only; open-bus readback is not modeled.
@ -156,9 +166,10 @@ impl Audio {
self.wave[self.wave_bank()][(address - WAVE_RAM) as usize] = value;
continue;
}
if self.enabled && (SOUND_START..=SOUND_START + 5).contains(&address) {
self.pulse
.write(address - SOUND_START, value, self.next_step);
if let Some((index, offset)) = Self::pulse_register(address) {
if self.enabled {
self.pulses[index].write(offset, value, self.next_step);
}
continue;
}
let shift = (address & 1) * 8;
@ -181,7 +192,7 @@ impl Audio {
SOUNDCNT_X if address & 1 == 0 => {
if self.enabled && value & 0x80 == 0 {
self.psg = [0; 17];
self.pulse = Pulse::default();
self.pulses = [Pulse::default(); 2];
for fifo in &mut self.fifo {
fifo.reset_queue();
}
@ -207,11 +218,15 @@ impl Audio {
}
while cycles != 0 {
let count = cycles.min(SEQUENCER_PERIOD - u32::from(self.sequencer_phase));
self.pulse.advance(count);
for pulse in &mut self.pulses {
pulse.advance(count);
}
let phase = u32::from(self.sequencer_phase) + count;
if phase == SEQUENCER_PERIOD {
self.sequencer_phase = 0;
self.pulse.clock(self.next_step);
for pulse in &mut self.pulses {
pulse.clock(self.next_step);
}
self.next_step = (self.next_step + 1) & 7;
} else {
self.sequencer_phase = phase as u16;
@ -256,10 +271,15 @@ impl Audio {
let psg_control = self.psg[16];
let ratio = [1, 2, 4, 0][usize::from(self.control & 3)];
for (side, level) in sides.iter_mut().enumerate() {
if psg_control & (1 << (8 + side * 4)) != 0 {
let volume = ((psg_control >> (side * 4)) & 7) as i16 + 1;
*level += (self.pulse.sample() * volume * ratio) >> 2;
let mut psg_sample = 0;
for (index, pulse) in self.pulses.iter().enumerate() {
if psg_control & (1 << (8 + side * 4 + index)) != 0 {
psg_sample += pulse.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;
*level = (*level + (self.bias & 0x3ff) as i16).clamp(0, 1023) - 512;
}
StereoLevel {