With the Electron as a test bed, start to simplify audio class groups.

Concurrency/AsyncTaskQueue.hpp

@@ -40,9 +40,12 @@ private:
 /// An implementation detail; provides a no-op implementation of time advances for TaskQueues without a Performer.
 template <> struct TaskQueueStorage<void> {
 	TaskQueueStorage() {}
+protected:
+	void update() {}
+};
 
-	protected:
-		void update() {}
+struct EnqueueDelegate {
+	virtual std::function<void(void)> prepare_enqueue() = 0;
 };
 
 /*!
@@ -67,10 +70,15 @@ template <> struct TaskQueueStorage<void> {
 template <
 	bool perform_automatically,
 	bool start_immediately = true,
+	bool use_enqueue_delegate = false,
 	typename Performer = void
 >
 class AsyncTaskQueue: public TaskQueueStorage<Performer> {
 public:
+	void set_enqueue_delegate(EnqueueDelegate *const delegate) {
+		enqueue_delegate_ = delegate;
+	}
+
 	template <typename... Args> AsyncTaskQueue(Args&&... args) :
 		TaskQueueStorage<Performer>(std::forward<Args>(args)...) {
 		if constexpr (start_immediately) {
@@ -90,6 +98,9 @@ public:
 	/// to 'now'.
 	void enqueue(const std::function<void(void)> &post_action) {
 		const std::lock_guard guard(condition_mutex_);
+		if constexpr (use_enqueue_delegate) {
+			actions_.push_back(enqueue_delegate_->prepare_enqueue());
+		}
 		actions_.push_back(post_action);
 
 		if constexpr (perform_automatically) {
@@ -206,6 +217,8 @@ private:
 		};
 	}
 
+	EnqueueDelegate *enqueue_delegate_ = nullptr;
+
 	// The list of actions waiting be performed. These will be elided,
 	// increasing their latency, if the emulation thread falls behind.
 	using ActionVector = std::vector<std::function<void(void)>>;

Machines/Acorn/Electron/Electron.cpp

@@ -15,7 +15,6 @@
 #include "ClockReceiver/ClockReceiver.hpp"
 #include "ClockReceiver/ForceInline.hpp"
 #include "Configurable/StandardOptions.hpp"
-#include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
 #include "Processors/6502/6502.hpp"
 
 #include "Storage/MassStorage/SCSI/SCSI.hpp"
@@ -27,6 +26,9 @@
 
 #include "ClockReceiver/JustInTime.hpp"
 
+#include "Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
+#include "Outputs/Speaker/SpeakerQueue.hpp"
+
 #include "Interrupts.hpp"
 #include "Keyboard.hpp"
 #include "Plus3.hpp"
@@ -58,8 +60,7 @@ public:
 			hard_drive_(scsi_bus_, 0),
 			scsi_device_(scsi_bus_.add_device()),
 			video_(ram_),
-			sound_generator_(audio_queue_),
-			speaker_(sound_generator_) {
+			audio_(SoundGenerator::clock_rate_divider) {
 		memset(key_states_, 0, sizeof(key_states_));
 		for(int c = 0; c < 16; c++)
 			memset(roms_[c], 0xff, 16384);
@@ -67,8 +68,8 @@ public:
 		tape_.set_delegate(this);
 		set_clock_rate(2000000);
 
-		speaker_.set_input_rate(2000000 / SoundGenerator::clock_rate_divider);
-		speaker_.set_high_frequency_cutoff(6000);
+		audio_.speaker.set_input_rate(2000000 / SoundGenerator::clock_rate_divider);
+		audio_.speaker.set_high_frequency_cutoff(6000);
 
 		::ROM::Request request = ::ROM::Request(::ROM::Name::AcornBASICII) && ::ROM::Request(::ROM::Name::AcornElectronMOS100);
 		if(target.has_pres_adfs) {
@@ -143,7 +144,7 @@ public:
 	}
 
 	~ConcreteMachine() {
-		audio_queue_.lock_flush();
+		audio_.stop();
 	}
 
 	void set_key_state(uint16_t key, bool isPressed) final {
@@ -234,8 +235,7 @@ public:
 		const auto [cycles, video_interrupts] = run_for_access(address);
 		signal_interrupt(video_interrupts);
 
-		cycles_since_audio_update_ += cycles;
-		if(cycles_since_audio_update_ > Cycles(16384)) update_audio();
+		audio_ += cycles;
 		tape_.run_for(cycles);
 
 		if(typer_) typer_->run_for(cycles);
@@ -278,8 +278,7 @@ public:
 						// update speaker mode
 						bool new_speaker_is_enabled = (*value & 6) == 2;
 						if(new_speaker_is_enabled != speaker_is_enabled_) {
-							update_audio();
-							sound_generator_.set_is_enabled(new_speaker_is_enabled);
+							audio_.generator.set_is_enabled(new_speaker_is_enabled);
 							speaker_is_enabled_ = new_speaker_is_enabled;
 						}
 
@@ -340,8 +339,7 @@ public:
 				break;
 				case 0xfe06:
 					if(!is_read(operation)) {
-						update_audio();
-						sound_generator_.set_divider(*value);
+						audio_.generator.set_divider(*value);
 						tape_.set_counter(*value);
 					}
 				break;
@@ -510,8 +508,7 @@ public:
 
 	void flush_output(int outputs) final {
 		if(outputs & Output::Audio) {
-			update_audio();
-			audio_queue_.perform();
+			audio_.perform();
 		}
 	}
 
@@ -532,7 +529,7 @@ public:
 	}
 
 	Outputs::Speaker::Speaker *get_speaker() final {
-		return &speaker_;
+		return &audio_.speaker;
 	}
 
 	void run_for(const Cycles cycles) final {
@@ -682,10 +679,6 @@ private:
 	}
 
 	// MARK: - Work deferral updates.
-	inline void update_audio() {
-		speaker_.run_for(audio_queue_, cycles_since_audio_update_.divide(Cycles(SoundGenerator::clock_rate_divider)));
-	}
-
 	inline void signal_interrupt(uint8_t interrupt) {
 		if(!interrupt) {
 			return;
@@ -732,9 +725,6 @@ private:
 	uint8_t key_states_[14];
 	Electron::KeyboardMapper keyboard_mapper_;
 
-	// Counters related to simultaneous subsystems
-	Cycles cycles_since_audio_update_ = 0;
-
 	// Tape
 	Tape tape_;
 	bool use_fast_tape_hack_ = false;
@@ -771,9 +761,10 @@ private:
 	// Outputs
 	VideoOutput video_;
 
-	Concurrency::AsyncTaskQueue<false> audio_queue_;
-	SoundGenerator sound_generator_;
-	Outputs::Speaker::PullLowpass<SoundGenerator> speaker_;
+	Outputs::Speaker::SpeakerQueue<
+		Outputs::Speaker::PullLowpass<SoundGenerator>,
+		SoundGenerator
+	> audio_;
 
 	bool speaker_is_enabled_ = false;
 

Machines/Acorn/Electron/SoundGenerator.cpp

@@ -12,7 +12,7 @@
 
 using namespace Electron;
 
-SoundGenerator::SoundGenerator(Concurrency::AsyncTaskQueue<false> &audio_queue) :
+SoundGenerator::SoundGenerator(Outputs::Speaker::TaskQueue &audio_queue) :
 	audio_queue_(audio_queue) {}
 
 void SoundGenerator::set_sample_volume_range(std::int16_t range) {
@@ -40,13 +40,13 @@ template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Mix>(std::
 template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Store>(std::size_t, Outputs::Speaker::MonoSample *);
 template void SoundGenerator::apply_samples<Outputs::Speaker::Action::Ignore>(std::size_t, Outputs::Speaker::MonoSample *);
 
-void SoundGenerator::set_divider(uint8_t divider) {
+void SoundGenerator::set_divider(const uint8_t divider) {
 	audio_queue_.enqueue([this, divider]() {
 		divider_ = divider * 32 / clock_rate_divider;
 	});
 }
 
-void SoundGenerator::set_is_enabled(bool is_enabled) {
+void SoundGenerator::set_is_enabled(const bool is_enabled) {
 	audio_queue_.enqueue([this, is_enabled]() {
 		is_enabled_ = is_enabled;
 		counter_ = 0;

Machines/Acorn/Electron/SoundGenerator.hpp

@@ -9,13 +9,13 @@
 #pragma once
 
 #include "Outputs/Speaker/Implementation/BufferSource.hpp"
-#include "Concurrency/AsyncTaskQueue.hpp"
+#include "Outputs/Speaker/SpeakerQueue.hpp"
 
 namespace Electron {
 
 class SoundGenerator: public ::Outputs::Speaker::BufferSource<SoundGenerator, false> {
 public:
-	SoundGenerator(Concurrency::AsyncTaskQueue<false> &);
+	SoundGenerator(Outputs::Speaker::TaskQueue &);
 
 	void set_divider(uint8_t);
 	void set_is_enabled(bool);
@@ -28,7 +28,7 @@ public:
 	void set_sample_volume_range(std::int16_t range);
 
 private:
-	Concurrency::AsyncTaskQueue<false> &audio_queue_;
+	Outputs::Speaker::TaskQueue &audio_queue_;
 	unsigned int counter_ = 0;
 	unsigned int divider_ = 0;
 	bool is_enabled_ = false;

OSBindings/Mac/Clock Signal.xcodeproj/project.pbxproj

@@ -2523,6 +2523,7 @@
 		4BEF6AA81D35CE9E00E73575 /* DigitalPhaseLockedLoopBridge.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = DigitalPhaseLockedLoopBridge.h; sourceTree = "<group>"; };
 		4BEF6AA91D35CE9E00E73575 /* DigitalPhaseLockedLoopBridge.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = DigitalPhaseLockedLoopBridge.mm; sourceTree = "<group>"; };
 		4BEF6AAB1D35D1C400E73575 /* DPLLTests.swift */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.swift; path = DPLLTests.swift; sourceTree = "<group>"; };
+		4BEF9CA92EC8294E00DDD0F6 /* SpeakerQueue.hpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.h; path = SpeakerQueue.hpp; sourceTree = "<group>"; };
 		4BF0BC67297108D100CCA2B5 /* MemorySlotHandler.cpp */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.cpp.cpp; path = MemorySlotHandler.cpp; sourceTree = "<group>"; };
 		4BF0BC6F2973318E00CCA2B5 /* RP5C01.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = RP5C01.cpp; sourceTree = "<group>"; };
 		4BF0BC702973318E00CCA2B5 /* RP5C01.hpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.h; path = RP5C01.hpp; sourceTree = "<group>"; };
@@ -5312,6 +5313,7 @@
 		4BD060A41FE49D3C006E14BE /* Speaker */ = {
 			isa = PBXGroup;
 			children = (
+				4BEF9CA92EC8294E00DDD0F6 /* SpeakerQueue.hpp */,
 				4BD060A51FE49D3C006E14BE /* Speaker.hpp */,
 				4B8EF6051FE5AF830076CCDD /* Implementation */,
 			);

OSBindings/Mac/Clock Signal/Machine/CSMachine.mm

@@ -39,7 +39,7 @@
 namespace {
 
 struct MachineUpdater {
-	void perform(Time::Nanos duration) {
+	void perform(const Time::Nanos duration) {
 		// Top out at 1/20th of a second; this is a safeguard against a negative
 		// feedback loop if emulation starts running slowly.
 		const auto seconds = std::min(Time::seconds(duration), 0.05);
@@ -51,7 +51,7 @@ struct MachineUpdater {
 	MachineTypes::TimedMachine *timed_machine = nullptr;
 };
 
-using Updater = Concurrency::AsyncTaskQueue<true, false, MachineUpdater>;
+using Updater = Concurrency::AsyncTaskQueue<true, false, false, MachineUpdater>;
 
 }
 

Outputs/Speaker/Implementation/BufferSource.hpp

@@ -9,6 +9,7 @@
 #pragma once
 
 #include "Outputs/Speaker/Speaker.hpp"
+#include "Concurrency/AsyncTaskQueue.hpp"
 
 #include <algorithm>
 #include <array>
@@ -26,7 +27,7 @@ enum class Action {
 	Ignore,
 };
 
-template <Action action, typename SampleT> void apply(SampleT &lhs, SampleT rhs) {
+template <Action action, typename SampleT> void apply(SampleT &lhs, const SampleT rhs) {
 	switch(action) {
 		case Action::Mix:	lhs += rhs;	break;
 		case Action::Store:	lhs = rhs;	break;
@@ -34,7 +35,8 @@ template <Action action, typename SampleT> void apply(SampleT &lhs, SampleT rhs)
 	}
 }
 
-template <Action action, typename IteratorT, typename SampleT> void fill(IteratorT begin, IteratorT end, SampleT value) {
+template <Action action, typename IteratorT, typename SampleT>
+void fill(IteratorT begin, const IteratorT end, const SampleT value) {
 	switch(action) {
 		case Action::Mix:
 			while(begin != end) {
@@ -56,45 +58,45 @@ template <Action action, typename IteratorT, typename SampleT> void fill(Iterato
 */
 template <typename SourceT, bool stereo>
 class BufferSource {
-	public:
-		/*!
-			Indicates whether this component will write stereo samples.
-		*/
-		static constexpr bool is_stereo = stereo;
+public:
+	/*!
+		Indicates whether this component will write stereo samples.
+	*/
+	static constexpr bool is_stereo = stereo;
 
-		/*!
-			Should 'apply' the next @c number_of_samples to @c target ; application means applying @c action which can be achieved either via the
-			helper functions above — @c apply and @c fill — or by semantic inspection (primarily, if an obvious quick route for @c Action::Ignore is available).
+	/*!
+		Should 'apply' the next @c number_of_samples to @c target ; application means applying @c action which can be achieved either via the
+		helper functions above — @c apply and @c fill — or by semantic inspection (primarily, if an obvious quick route for @c Action::Ignore is available).
 
-			No default implementation is provided.
-		*/
-		template <Action action>
-		void apply_samples(std::size_t number_of_samples, typename SampleT<stereo>::type *target);
+		No default implementation is provided.
+	*/
+	template <Action action>
+	void apply_samples(std::size_t number_of_samples, typename SampleT<stereo>::type *);
 
-		/*!
-			@returns @c true if it is trivially true that a call to get_samples would just
-				fill the target with zeroes; @c false if a call might return all zeroes or
-				might not.
-		*/
-//		bool is_zero_level() const						{	return false;	}
+	/*!
+		@returns @c true if it is trivially true that a call to get_samples would just
+			fill the target with zeroes; @c false if a call might return all zeroes or
+			might not.
+	*/
+//	bool is_zero_level() const						{	return false;	}
 
-		/*!
-			Sets the proper output range for this sample source; it should write values
-			between 0 and volume.
-		*/
-//		void set_sample_volume_range(std::int16_t volume);
+	/*!
+		Sets the proper output range for this sample source; it should write values
+		between 0 and volume.
+	*/
+//	void set_sample_volume_range(std::int16_t volume);
 
-		/*!
-			Permits a sample source to declare that, averaged over time, it will use only
-			a certain proportion of the allocated volume range. This commonly happens
-			in sample sources that use a time-multiplexed sound output — for example, if
-			one were to output only every other sample then it would return 0.5.
+	/*!
+		Permits a sample source to declare that, averaged over time, it will use only
+		a certain proportion of the allocated volume range. This commonly happens
+		in sample sources that use a time-multiplexed sound output — for example, if
+		one were to output only every other sample then it would return 0.5.
 
-			This is permitted to vary over time but there is no contract as to when it will be
-			used by a speaker. If it varies, it should do so very infrequently and only to
-			represent changes in hardware configuration.
-		*/
-		double average_output_peak() const { return 1.0; }
+		This is permitted to vary over time but there is no contract as to when it will be
+		used by a speaker. If it varies, it should do so very infrequently and only to
+		represent changes in hardware configuration.
+	*/
+	double average_output_peak() const { return 1.0; }
 };
 
 ///
@@ -140,7 +142,7 @@ public:
 
 	// TODO: use a concept here, when C++20 filters through.
 	//
-	// Until then: sample sources should implement this.
+	// Until then: sample sources can implement this rather than apply_samples.
 //	typename SampleT<stereo>::type level() const;
 //	void advance();
 

Outputs/Speaker/Implementation/LowpassSpeaker.hpp

@@ -10,6 +10,7 @@
 
 #include "BufferSource.hpp"
 #include "Outputs/Speaker/Speaker.hpp"
+#include "Outputs/Speaker/SpeakerQueue.hpp"
 #include "SignalProcessing/FIRFilter.hpp"
 #include "ClockReceiver/ClockReceiver.hpp"
 #include "Concurrency/AsyncTaskQueue.hpp"
@@ -375,10 +376,13 @@ public:
 		if(cycles == Cycles(0)) {
 			return;
 		}
+		queue.enqueue(update_for(cycles));
+	}
 
-		queue.enqueue([this, cycles] {
+	std::function<void(void)> update_for(const Cycles cycles) {
+		return [this, cycles] {
 			run_for(cycles);
-		});
+		};
 	}
 
 private:

Outputs/Speaker/SpeakerQueue.hpp

@@ -0,0 +1,52 @@
+//
+//  SpeakerQueue.hpp
+//  Clock Signal
+//
+//  Created by Thomas Harte on 14/11/2025.
+//  Copyright © 2025 Thomas Harte. All rights reserved.
+//
+
+#pragma once
+
+#include "Concurrency/AsyncTaskQueue.hpp"
+#include "ClockReceiver/ClockReceiver.hpp"
+
+namespace Outputs::Speaker {
+using TaskQueue = Concurrency::AsyncTaskQueue<false, true, true>;
+
+template <typename SpeakerT, typename GeneratorT>
+struct SpeakerQueue: private Concurrency::EnqueueDelegate {
+private:
+	TaskQueue queue_;
+
+public:
+	SpeakerQueue(const Cycles divider) : generator(queue_), speaker(generator), divider_(divider) {
+		queue_.set_enqueue_delegate(this);
+	}
+
+	GeneratorT generator;
+	SpeakerT speaker;
+
+	void operator += (const Cycles &duration) {
+		cycles_since_update_ += duration;
+	}
+
+	void stop() {
+		queue_.stop();
+	}
+
+	void perform() {
+		// TODO: is there a way to avoid the empty lambda?
+		queue_.enqueue([]() {});
+		queue_.perform();
+	}
+
+private:
+	Cycles divider_;
+	Cycles cycles_since_update_;
+
+	std::function<void(void)> prepare_enqueue() {
+		return speaker.update_for(cycles_since_update_.divide(divider_));
+	}
+};
+}