M include/mgba/internal/gb/audio.h → include/mgba/internal/gb/audio.h

@@ -137,6 +137,9 @@ bool stop;
 	int length;
 
 	uint32_t lfsr;
+	int nSamples;
+	int samples;
+
 	int8_t sample;
 };
 

M src/gb/audio.c → src/gb/audio.c

@@ -37,6 +37,8 @@
 static void _updateSquareSample(struct GBAudioSquareChannel* ch);
 static int32_t _updateSquareChannel(struct GBAudioSquareChannel* ch);
 
+static int8_t _coalesceNoiseChannel(struct GBAudioNoiseChannel* ch);
+
 static void _updateFrame(struct mTiming* timing, void* user, uint32_t cyclesLate);
 static void _updateChannel1(struct mTiming* timing, void* user, uint32_t cyclesLate);
 static void _updateChannel2(struct mTiming* timing, void* user, uint32_t cyclesLate);
@@ -118,6 +120,7 @@ }
 	audio->ch1 = (struct GBAudioSquareChannel) { .envelope = { .dead = 2 } };
 	audio->ch2 = (struct GBAudioSquareChannel) { .envelope = { .dead = 2 } };
 	audio->ch3 = (struct GBAudioWaveChannel) { .bank = 0 };
+	audio->ch4 = (struct GBAudioNoiseChannel) { .nSamples = 0 };
 	// TODO: DMG randomness
 	audio->ch3.wavedata8[0] = 0x00;
 	audio->ch3.wavedata8[1] = 0xFF;
@@ -564,11 +567,13 @@ if (audio->playingCh4 && !audio->ch4.envelope.dead) {
 			--audio->ch4.envelope.nextStep;
 			if (audio->ch4.envelope.nextStep == 0) {
 				int8_t sample = audio->ch4.sample > 0;
+				audio->ch4.samples -= audio->ch4.sample;
 				_updateEnvelope(&audio->ch4.envelope);
 				if (audio->ch4.envelope.dead == 2) {
 					mTimingDeschedule(timing, &audio->ch4Event);
 				}
 				audio->ch4.sample = sample * audio->ch4.envelope.currentVolume;
+				audio->ch4.samples += audio->ch4.sample;
 			}
 		}
 		break;
@@ -611,12 +616,13 @@ }
 	}
 
 	if (audio->playingCh4 && !audio->forceDisableCh[3]) {
+		int8_t sample = _coalesceNoiseChannel(&audio->ch4);
 		if (audio->ch4Left) {
-			sampleLeft += audio->ch4.sample;
+			sampleLeft += sample;
 		}
 
 		if (audio->ch4Right) {
-			sampleRight += audio->ch4.sample;
+			sampleRight += sample;
 		}
 	}
 
@@ -745,6 +751,17 @@ return period * 4;
 	}
 }
 
+static int8_t _coalesceNoiseChannel(struct GBAudioNoiseChannel* ch) {
+	if (!ch->nSamples) {
+		return ch->sample;
+	}
+	// TODO keep track of timing
+	int8_t sample = ch->samples / ch->nSamples;
+	ch->nSamples = 0;
+	ch->samples = 0;
+	return sample;
+}
+
 static void _updateEnvelope(struct GBAudioEnvelope* envelope) {
 	if (envelope->direction) {
 		++envelope->currentVolume;
@@ -895,18 +912,17 @@ static void _updateChannel4(struct mTiming* timing, void* user, uint32_t cyclesLate) {
 	struct GBAudio* audio = user;
 	struct GBAudioNoiseChannel* ch = &audio->ch4;
 
-	int32_t baseCycles = ch->ratio ? 2 * ch->ratio : 1;
-	baseCycles <<= ch->frequency;
-	baseCycles *= 8 * audio->timingFactor;
-	int32_t cycles = 0;
+	int32_t cycles = ch->ratio ? 2 * ch->ratio : 1;
+	cycles <<= ch->frequency;
+	cycles *= 8 * audio->timingFactor;
+
+	int lsb = ch->lfsr & 1;
+	ch->sample = lsb * ch->envelope.currentVolume;
+	++ch->nSamples;
+	ch->samples += ch->sample;
+	ch->lfsr >>= 1;
+	ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
 
-	do {
-		int lsb = ch->lfsr & 1;
-		ch->sample = lsb * ch->envelope.currentVolume;
-		ch->lfsr >>= 1;
-		ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
-		cycles += baseCycles;
-	} while (cycles + baseCycles < audio->sampleInterval);
 	mTimingSchedule(timing, &audio->ch4Event, cycles - cyclesLate);
 }