From 5d4e22ebc9f679cea041beead8269d626d7906f9 Mon Sep 17 00:00:00 2001
From: athrxx
Date: Wed, 23 Jan 2019 21:28:21 +0100
Subject: SCI: (PC-98 driver) - frequency bug workaround

The square sound channels will be out of spec when playing on the lowest octave. The result is a rather ugly noise. This bug makes a rather subtle appearance if the channel remapping is accurate, but it becomes quite obvious in the SQ4 intro with the current implementation. This commit turns off the channel when trying to play out of spec.
---
 engines/sci/sound/drivers/pc9801.cpp | 26 ++++++++++++++++++--------
 1 file changed, 18 insertions(+), 8 deletions(-)

(limited to 'engines')

diff --git a/engines/sci/sound/drivers/pc9801.cpp b/engines/sci/sound/drivers/pc9801.cpp
index 8a1521a0e2..2b99d6b2a2 100644
--- a/engines/sci/sound/drivers/pc9801.cpp
+++ b/engines/sci/sound/drivers/pc9801.cpp
@@ -111,7 +111,7 @@ protected:
 
 private:
 	virtual void programChange(uint8 program) = 0;
-	virtual void prepareFrequencyAndVolume(bool updateVolume);
+	virtual bool prepareFrequencyAndVolume(bool updateVolume);
 	virtual void sendSoundOnOff(bool noteOn) = 0;
 	virtual void sendFrequency() = 0;
 	virtual void sendVolume() = 0;	
@@ -156,7 +156,7 @@ public:
 
 private:
 	void programChange(uint8 program);
-	void prepareFrequencyAndVolume(bool updateVolume);
+	bool prepareFrequencyAndVolume(bool updateVolume);
 	void processSounds();
 	void sendSoundOnOff(bool noteOn);
 	void sendVolume();
@@ -406,7 +406,9 @@ void SoundChannel_PC9801::processNoteEvent(uint8 note, bool noteOn) {
 		_flags |= kChanVbrRestartEnv;
 	}
 
-	prepareFrequencyAndVolume(noteOn);
+	if (!prepareFrequencyAndVolume(noteOn))
+		noteOn = false;
+
 	sendSoundOnOff(noteOn);
 }
 
@@ -480,6 +482,8 @@ int SoundChannel_PC9801::recalculateFrequency(uint16 note, uint16 modifier, uint
 
 	if (_type != 2)
 		res |= (block << 11);
+	else if (block == 0)
+		return -1;
 
 	if (pb)
 		res += (((pb * pitchVbrMultiplier) & 0x0FF0) >> 8);
@@ -591,12 +595,15 @@ void SoundChannel_PC9801::writeReg(uint8 part, uint8 reg, uint8 val) {
 	_pc98a->writeReg(part, reg, val);
 }
 
-void SoundChannel_PC9801::prepareFrequencyAndVolume(bool updateVolume) {
+bool SoundChannel_PC9801::prepareFrequencyAndVolume(bool updateVolume) {
 	if (recalculateFrequency(_note, 0, &_frequencyBlock, &_frequencyCourse, &_frequencyNoteModifier) == -1)
-		return;
+		return false;
+
 	sendFrequency();
 	if (updateVolume)
 		sendVolume();
+
+	return true;
 }
 
 SoundChannel_PC9801_FM4OP::SoundChannel_PC9801_FM4OP(uint8 id, PC98AudioCore *pc98a, MidiPart_PC9801 **parts, SciVersion version, SciSpan<const uint8> instrumentData, uint8 patchSize, bool &soundOn)
@@ -736,14 +743,17 @@ void SoundChannel_PC9801_FM2OP::programChange(uint8 program) {
 		writeReg(_regPrt, i, data[pos++]);
 }
 
-void SoundChannel_PC9801_FM2OP::prepareFrequencyAndVolume(bool updateVolume) {
+bool SoundChannel_PC9801_FM2OP::prepareFrequencyAndVolume(bool updateVolume) {
 	if (recalculateFrequency(_note, _opFreqOffset[_operatorFrqIndex[0]], 0, &_frequencyCourse, &_frequencyNoteModifier) == -1)
-		return;
+		return false;
 	if (recalculateFrequency(_note, _opFreqOffset[_operatorFrqIndex[1]], 0, &_frequencyCourse2, &_frequencyNoteModifier2) == -1)
-		return;
+		return false;
+
 	sendFrequency();
 	if (updateVolume)
 		sendVolume();
+
+	return true;
 }
 
 void SoundChannel_PC9801_FM2OP::sendSoundOnOff(bool noteOn) {
-- 
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