From d01e1f3bb13a7ac0b017cdc591bb9683b4422b05 Mon Sep 17 00:00:00 2001
From: Thomas Harte <thomas.harte@gmail.com>
Date: Thu, 13 Nov 2025 17:34:57 -0500
Subject: [PATCH] Block and synchronise threads for voice 3 readback.

---
 Components/SID/SID.cpp | 19 ++++++++++++++++---
 Components/SID/SID.hpp | 11 +++--------
 2 files changed, 19 insertions(+), 11 deletions(-)

diff --git a/Components/SID/SID.cpp b/Components/SID/SID.cpp
index 3cb5f85da..390654f38 100644
--- a/Components/SID/SID.cpp
+++ b/Components/SID/SID.cpp
@@ -133,8 +133,18 @@ void SID::update_filter() {
 }
 
 uint8_t SID::read(const Numeric::SizedInt<5> address) {
-	(void)address;
-	return last_write_;
+	switch(address.get()) {
+		default:	return last_write_;
+
+		case 0x19:	return 0x00;	// TODO: potentometer x.
+		case 0x1a:	return 0x00;	// TODO: potentometer y.
+
+		case 0x1b:
+		case 0x1c:
+			// Ensure all channels are entirely up to date.
+			audio_queue_.flush();
+			return (address == 0x1c) ? voices_[2].adsr.envelope : uint8_t(voices_[2].output(voices_[1]) >> 4);
+	}
 }
 
 // MARK: - Oscillators.
@@ -160,7 +170,7 @@ uint16_t Voice::Oscillator::sawtooth_output() const {
 
 uint16_t Voice::NoiseGenerator::output() const {
 	// Uses bits: 20, 18, 14, 11, 9, 5, 2 and 0, plus four more zero bits.
-	return
+	const uint16_t output =
 		((noise >> 9) & 0b1000'0000'0000) |		// b20 -> b11
 		((noise >> 8) & 0b0100'0000'0000) |		// b18 -> b10
 		((noise >> 5) & 0b0010'0000'0000) |		// b14 -> b9
@@ -169,6 +179,9 @@ uint16_t Voice::NoiseGenerator::output() const {
 		((noise << 1) & 0b0000'0100'0000) |		// b5 -> b6
 		((noise << 3) & 0b0000'0010'0000) |		// b2 -> b5
 		((noise << 4) & 0b0000'0001'0000);		// b0 -> b4
+
+	assert(output <= Voice::MaxWaveformValue);
+	return output;
 }
 
 void Voice::NoiseGenerator::update(const bool test) {
diff --git a/Components/SID/SID.hpp b/Components/SID/SID.hpp
index c3d9f6499..79a0b3ee6 100644
--- a/Components/SID/SID.hpp
+++ b/Components/SID/SID.hpp
@@ -17,6 +17,8 @@
 namespace MOS::SID {
 
 struct Voice {
+	static constexpr uint16_t MaxWaveformValue = (1 << 12) - 1;
+
 	struct Oscillator {
 		// Programmer inputs.
 		uint32_t pitch = 0;
@@ -84,8 +86,6 @@ private:
 	bool sync() const;
 	bool gate() const;
 
-	static constexpr uint16_t MaxWaveformValue = (1 << 12) - 1;
-
 	uint16_t pulse_output() const;
 	uint16_t triangle_output(const Voice &prior) const;
 };
@@ -99,17 +99,12 @@ public:
 
 	// Outputs::Speaker::BufferSource.
 	template <Outputs::Speaker::Action action>
-		void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target);
+		void apply_samples(std::size_t, Outputs::Speaker::MonoSample *);
 	bool is_zero_level() const;
 	void set_sample_volume_range(std::int16_t);
 
 private:
 	Concurrency::AsyncTaskQueue<false> &audio_queue_;
-
-	// TODO: an emulator thread copy of voices needs to be kept too, to do the digital stuff, as
-	// the current output of voice 3 can be read. Probably best if the audio thread posts its most
-	// recent copy atomically and the emulator thread just catches up from whatever it has? I don't
-	// think that spinning on voice 3 is common.
 	Voice voices_[3];
 
 	uint8_t last_write_;