From 8bcbcd6c167e8e7169f006da459f3cbe450a4a59 Mon Sep 17 00:00:00 2001
From: Matthew Hoops
Date: Wed, 29 Apr 2015 23:45:25 -0400
Subject: AUDIO: Change callback frequency without restarting the audio stream

---
 audio/fmopl.cpp | 33 +++++++++++----------------------
 audio/fmopl.h   | 12 ++++--------
 2 files changed, 15 insertions(+), 30 deletions(-)

diff --git a/audio/fmopl.cpp b/audio/fmopl.cpp
index 638da6c224..9af7afff54 100644
--- a/audio/fmopl.cpp
+++ b/audio/fmopl.cpp
@@ -183,14 +183,6 @@ void OPL::stop() {
 	_callback.reset();
 }
 
-void OPL::setCallbackFrequency(int timerFrequency) {
-	if (!isRunning())
-		return;
-
-	stopCallbacks();
-	startCallbacks(timerFrequency);
-}
-
 bool OPL::_hasInstance = false;
 
 EmulatedOPL::EmulatedOPL() :
@@ -239,6 +231,17 @@ int EmulatedOPL::getRate() const {
 }
 
 void EmulatedOPL::startCallbacks(int timerFrequency) {
+	setCallbackFrequency(timerFrequency);
+	// TODO: Eventually start mixer playback here
+	//g_system->getMixer()->playStream(Audio::Mixer::kPlainSoundType, _handle, this, -1, Audio::Mixer::kMaxChannelVolume, 0, DisposeAfterUse::NO, true);
+}
+
+void EmulatedOPL::stopCallbacks() {
+	// TODO: Eventually stop mixer playback here
+	//g_system->getMixer()->stopHandle(*_handle);
+}
+
+void EmulatedOPL::setCallbackFrequency(int timerFrequency) {
 	_baseFreq = timerFrequency;
 	assert(_baseFreq != 0);
 
@@ -249,20 +252,6 @@ void EmulatedOPL::startCallbacks(int timerFrequency) {
 	// but less prone to arithmetic overflow.
 
 	_samplesPerTick = (d << FIXP_SHIFT) + (r << FIXP_SHIFT) / _baseFreq;
-
-	// TODO: Eventually start mixer playback here
-	//g_system->getMixer()->playStream(Audio::Mixer::kPlainSoundType, _handle, this, -1, Audio::Mixer::kMaxChannelVolume, 0, DisposeAfterUse::NO, true);
-}
-
-void EmulatedOPL::stopCallbacks() {
-	// TODO: Eventually stop mixer playback here
-	//g_system->getMixer()->stopHandle(*_handle);
-}
-
-bool EmulatedOPL::isRunning() const {
-	// TODO
-	//return g_system->getMixer()->isSoundHandleActive(*_handle);
-	return true;
 }
 
 } // End of namespace OPL
diff --git a/audio/fmopl.h b/audio/fmopl.h
index 243cd294e8..8baa9aa218 100644
--- a/audio/fmopl.h
+++ b/audio/fmopl.h
@@ -176,15 +176,10 @@ public:
 	void stop();
 
 	/**
-	 * Is the OPL running?
+	 * Change the callback frequency. This must only be called from a
+	 * timer proc.
 	 */
-	virtual bool isRunning() const = 0;
-
-	/**
-	 * Change the callback frequency. This has no effect if start()
-	 * has not already been called.
-	 */
-	void setCallbackFrequency(int timerFrequency);
+	virtual void setCallbackFrequency(int timerFrequency) = 0;
 
 	enum {
 		/**
@@ -218,6 +213,7 @@ public:
 	// OPL API
 	int readBuffer(int16 *buffer, const int numSamples);
 	bool isRunning() const;
+	void setCallbackFrequency(int timerFrequency);
 
 	int getRate() const;
 
-- 
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