From b515214fbeed84fe5532740b10ac677d94fca2cb Mon Sep 17 00:00:00 2001
From: Jeffrey Pfau <jeffrey@endrift.com>
Date: Sat, 24 Dec 2016 18:33:45 -0800
Subject: [PATCH] GB Audio: Reoptimize channel 4

---
 src/gb/audio.c  | 24 +++++++++++++++---------
 src/gba/audio.c |  1 +
 2 files changed, 16 insertions(+), 9 deletions(-)

diff --git a/src/gb/audio.c b/src/gb/audio.c
index 547ae49da..14f501096 100644
--- a/src/gb/audio.c
+++ b/src/gb/audio.c
@@ -873,15 +873,21 @@ static void _fadeChannel3(struct mTiming* timing, void* user, uint32_t cyclesLat
 static void _updateChannel4(struct mTiming* timing, void* user, uint32_t cyclesLate) {
 	struct GBAudio* audio = user;
 	struct GBAudioNoiseChannel* ch = &audio->ch4;
-	int lsb = ch->lfsr & 1;
-	ch->sample = lsb * 0x10 - 0x8;
-	ch->sample *= ch->envelope.currentVolume;
-	ch->lfsr >>= 1;
-	ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
-	int cycles = ch->ratio ? 2 * ch->ratio : 1;
-	cycles <<= ch->frequency;
-	cycles *= 8;
-	mTimingSchedule(timing, &audio->ch4Event, audio->timingFactor * cycles - cyclesLate);
+
+	int32_t baseCycles = ch->ratio ? 2 * ch->ratio : 1;
+	baseCycles <<= ch->frequency;
+	baseCycles *= 8 * audio->timingFactor;
+	int32_t cycles = 0;
+
+	do {
+		int lsb = ch->lfsr & 1;
+		ch->sample = lsb * 0x10 - 0x8;
+		ch->sample *= ch->envelope.currentVolume;
+		ch->lfsr >>= 1;
+		ch->lfsr ^= (lsb * 0x60) << (ch->power ? 0 : 8);
+		cycles += baseCycles;
+	} while (cycles < audio->sampleInterval);
+	mTimingSchedule(timing, &audio->ch4Event, cycles - cyclesLate);
 }
 
 void GBAudioPSGSerialize(const struct GBAudio* audio, struct GBSerializedPSGState* state, uint32_t* flagsOut) {
diff --git a/src/gba/audio.c b/src/gba/audio.c
index 4194f3a78..9f01889ed 100644
--- a/src/gba/audio.c
+++ b/src/gba/audio.c
@@ -73,6 +73,7 @@ void GBAAudioReset(struct GBAAudio* audio) {
 	audio->chBTimer = false;
 	audio->enable = false;
 	audio->sampleInterval = GBA_ARM7TDMI_FREQUENCY / audio->sampleRate;
+	audio->psg.sampleInterval = audio->sampleInterval;
 
 	blip_clear(audio->psg.left);
 	blip_clear(audio->psg.right);