From b2cf9a580bf9a417d955480a9c207225afc9bb75 Mon Sep 17 00:00:00 2001
From: Coen Rampen <crampen@gmail.com>
Date: Mon, 9 May 2022 15:27:36 +0200
Subject: [PATCH] AUDIO: Add AdLib MS driver callback frequency

This change allows a consumer to specify the desired timer callback frequency
for the AdLib multisource MIDI driver.
---
 audio/adlib_ms.cpp | 11 ++++++-----
 audio/adlib_ms.h   |  6 +++++-
 2 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/audio/adlib_ms.cpp b/audio/adlib_ms.cpp
index ae8c8546a08..56942d62c8c 100644
--- a/audio/adlib_ms.cpp
+++ b/audio/adlib_ms.cpp
@@ -394,7 +394,7 @@ bool MidiDriver_ADLIB_Multisource::detectOplType(OPL::Config::OplType oplType) {
 	return OPL::Config::detect(oplType) >= 0;
 }
 
-MidiDriver_ADLIB_Multisource::MidiDriver_ADLIB_Multisource(OPL::Config::OplType oplType) :
+MidiDriver_ADLIB_Multisource::MidiDriver_ADLIB_Multisource(OPL::Config::OplType oplType, int timerFrequency) :
 		_oplType(oplType),
 		_opl(nullptr),
 		_isOpen(false),
@@ -413,9 +413,11 @@ MidiDriver_ADLIB_Multisource::MidiDriver_ADLIB_Multisource(OPL::Config::OplType
 		_melodicChannels(nullptr),
 		_numMelodicChannels(0),
 		_noteCounter(1),
-		_oplFrequencyConversionFactor(pow(2, 20) / 49716.0f) {
+		_oplFrequencyConversionFactor(pow(2, 20) / 49716.0f),
+		_timerFrequency(timerFrequency) {
 	memset(_channelAllocations, 0xFF, sizeof(_channelAllocations));
 	Common::fill(_shadowRegisters, _shadowRegisters + sizeof(_shadowRegisters), 0);
+	_timerRate = 1000000 / _timerFrequency;
 }
 
 MidiDriver_ADLIB_Multisource::~MidiDriver_ADLIB_Multisource() {
@@ -463,10 +465,9 @@ int MidiDriver_ADLIB_Multisource::open() {
 	// Set default OPL register values.
 	initOpl();
 
-	_timerRate = getBaseTempo();
 	// Start the emulator / hardware interface. This will also start the timer
 	// callbacks.
-	_opl->start(new Common::Functor0Mem<void, MidiDriver_ADLIB_Multisource>(this, &MidiDriver_ADLIB_Multisource::onTimer));
+	_opl->start(new Common::Functor0Mem<void, MidiDriver_ADLIB_Multisource>(this, &MidiDriver_ADLIB_Multisource::onTimer), _timerFrequency);
 
 	return 0;
 }
@@ -533,7 +534,7 @@ uint32 MidiDriver_ADLIB_Multisource::property(int prop, uint32 param) {
 }
 
 uint32 MidiDriver_ADLIB_Multisource::getBaseTempo() {
-	return 1000000 / OPL::OPL::kDefaultCallbackFrequency;
+	return _timerRate;
 }
 
 MidiChannel *MidiDriver_ADLIB_Multisource::allocateChannel() {
diff --git a/audio/adlib_ms.h b/audio/adlib_ms.h
index 235ba8e3aa6..53231123c0a 100644
--- a/audio/adlib_ms.h
+++ b/audio/adlib_ms.h
@@ -589,8 +589,10 @@ public:
 	 * of OPL chip.
 	 * 
 	 * @param oplType The type of OPL chip that should be used.
+	 * @param timerFrequency The number of timer callbacks per second that
+	 * should be generated.
 	 */
-	MidiDriver_ADLIB_Multisource(OPL::Config::OplType oplType);
+	MidiDriver_ADLIB_Multisource(OPL::Config::OplType oplType, int timerFrequency = OPL::OPL::kDefaultCallbackFrequency);
 	~MidiDriver_ADLIB_Multisource();
 
 	/**
@@ -1118,6 +1120,8 @@ protected:
 
 	// True if the driver has been successfully opened.
 	bool _isOpen;
+	// The number of timer callbacks per second.
+	int _timerFrequency;
 	// Controls the behavior for calculating note frequency and volume.
 	AccuracyMode _accuracyMode;
 	// Controls the OPL channel allocation behavior.