From cd2ab70a58df83578f10a323b06be2e36e1cee28 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Sat, 25 Apr 2020 22:21:42 -0400
Subject: [PATCH] Moves the LFSR to the LowFrequencyOscillator.

Possibly I should come up with a better name for that?
---
 .../Implementation/LowFrequencyOscillator.cpp    |  4 ++++
 .../Implementation/LowFrequencyOscillator.hpp    | 16 +++++++++++++++-
 Components/OPL2/OPL2.cpp                         |  1 +
 Components/OPL2/OPL2.hpp                         |  4 ----
 4 files changed, 20 insertions(+), 5 deletions(-)

diff --git a/Components/OPL2/Implementation/LowFrequencyOscillator.cpp b/Components/OPL2/Implementation/LowFrequencyOscillator.cpp
index 930904b0d..142f3efb0 100644
--- a/Components/OPL2/Implementation/LowFrequencyOscillator.cpp
+++ b/Components/OPL2/Implementation/LowFrequencyOscillator.cpp
@@ -26,3 +26,7 @@ void LowFrequencyOscillator::update() {
 	// Vibrato is relatively simple: it's just three bits from the counter.
 	vibrato = (counter >> 10) & 7;
 }
+
+void LowFrequencyOscillator::update_lfsr() {
+	lfsr = noise_source_.next();
+}
diff --git a/Components/OPL2/Implementation/LowFrequencyOscillator.hpp b/Components/OPL2/Implementation/LowFrequencyOscillator.hpp
index d3c71669c..96fa4265d 100644
--- a/Components/OPL2/Implementation/LowFrequencyOscillator.hpp
+++ b/Components/OPL2/Implementation/LowFrequencyOscillator.hpp
@@ -9,6 +9,8 @@
 #ifndef LowFrequencyOscillator_hpp
 #define LowFrequencyOscillator_hpp
 
+#include "../../../Numeric/LFSR.hpp"
+
 namespace Yamaha {
 namespace OPL {
 
@@ -21,14 +23,26 @@ class LowFrequencyOscillator {
 	public:
 		/// Current attenuation due to tremolo / amplitude modulation, between 0 and 26.
 		int tremolo = 0;
+
 		/// A number between 0 and 7 indicating the current vibrato offset; this should be combined by operators
 		/// with their frequency number to get the actual vibrato.
 		int vibrato = 0;
+
 		/// A counter of the number of operator update cycles (i.e. input clock / 72) since an arbitrary time.
 		int counter = 0;
 
-		/// Updates the oscillator outputs
+		/// Describes the current output of the LFSR; will be either 0 or 1.
+		int lfsr = 0;
+
+		/// Updates the oscillator outputs. Should be called at the (input clock/72) rate.
 		void update();
+
+		/// Updartes the LFSR output. Should be called at the input clock rate.
+		void update_lfsr();
+
+	private:
+		// This is the correct LSFR per forums.submarine.org.uk.
+		Numeric::LFSR<int, 0x800302> noise_source_;
 };
 
 }
diff --git a/Components/OPL2/OPL2.cpp b/Components/OPL2/OPL2.cpp
index aa376215f..e4be97f71 100644
--- a/Components/OPL2/OPL2.cpp
+++ b/Components/OPL2/OPL2.cpp
@@ -68,6 +68,7 @@ void OPLL::get_samples(std::size_t number_of_samples, std::int16_t *target) {
 
 	while(number_of_samples--) {
 		if(!audio_offset_) update_all_chanels();
+		if(!(audio_offset_&3)) oscillator_.update_lfsr();
 
 		*target = int16_t(output_levels_[audio_offset_ / channel_output_period]);
 		++target;
diff --git a/Components/OPL2/OPL2.hpp b/Components/OPL2/OPL2.hpp
index 14a8420e5..b313f2472 100644
--- a/Components/OPL2/OPL2.hpp
+++ b/Components/OPL2/OPL2.hpp
@@ -11,7 +11,6 @@
 
 #include "../../Outputs/Speaker/Implementation/SampleSource.hpp"
 #include "../../Concurrency/AsyncTaskQueue.hpp"
-#include "../../Numeric/LFSR.hpp"
 
 #include "Implementation/Channel.hpp"
 #include "Implementation/Operator.hpp"
@@ -60,9 +59,6 @@ struct OPL2: public OPLBase<OPL2> {
 		Operator operators_[18];
 		Channel channels_[9];
 
-		// This is the correct LSFR per forums.submarine.org.uk.
-		Numeric::LFSR<uint32_t, 0x800302> noise_source_;
-
 		// Synchronous properties, valid only on the emulation thread.
 		uint8_t timers_[2] = {0, 0};
 		uint8_t timer_control_ = 0;