Adds a pipeline for audio output.

Machines/Amiga/Amiga.cpp

@@ -40,6 +40,7 @@ namespace Amiga {
 class ConcreteMachine:
 	public Activity::Source,
 	public CPU::MC68000::BusHandler,
+	public MachineTypes::AudioProducer,
 	public MachineTypes::JoystickMachine,
 	public MachineTypes::MappedKeyboardMachine,
 	public MachineTypes::MediaTarget,
@@ -183,10 +184,17 @@ class ConcreteMachine:
 		Chipset chipset_;
 		
 		// MARK: - Activity Source
+
 		void set_activity_observer(Activity::Observer *observer) final {
 			chipset_.set_activity_observer(observer);
 		}
 
+		// MARK: - MachineTypes::AudioProducer.
+
+		Outputs::Speaker::Speaker *get_speaker() final {
+			return chipset_.get_speaker();
+		}
+
 		// MARK: - MachineTypes::ScanProducer.
 
 		void set_scan_target(Outputs::Display::ScanTarget *scan_target) final {

Machines/Amiga/Audio.cpp

@@ -17,6 +17,17 @@
 
 using namespace Amiga;
 
+Audio::Audio(Chipset &chipset, uint16_t *ram, size_t word_size, float output_rate) :
+	DMADevice<4>(chipset, ram, word_size) {
+
+	// Mark all buffers as available.
+	for(auto &flag: buffer_available_) {
+		flag.store(true, std::memory_order::memory_order_relaxed);
+	}
+
+	speaker_.set_input_rate(output_rate);
+}
+
 bool Audio::advance_dma(int channel) {
 	switch(channels_[channel].state) {
 		case Channel::State::WaitingForDMA:
@@ -90,6 +101,28 @@ void Audio::output() {
 			posit_interrupt(interrupts[c]);
 		}
 	}
+
+	// TEMPORARY: just fill the audio buffer with silence.
+	if(!sample_pointer_) {
+		while(!buffer_available_[buffer_pointer_].load(std::memory_order::memory_order_relaxed));
+	}
+
+	buffer_[buffer_pointer_][sample_pointer_] = 0;
+	++sample_pointer_;
+
+	if(sample_pointer_ == buffer_[buffer_pointer_].size()) {
+		const auto &buffer = buffer_[buffer_pointer_];
+		auto &flag = buffer_available_[buffer_pointer_];
+
+		flag.store(false, std::memory_order::memory_order_release);
+		queue_.enqueue([this, &buffer, &flag] {
+			speaker_.push(buffer.data(), buffer.size());
+			flag.store(true, std::memory_order::memory_order_relaxed);
+		});
+
+		buffer_pointer_ = (buffer_pointer_ + 1) % BufferCount;
+		sample_pointer_ = 0;
+	}
 }
 
 /*

Machines/Amiga/Audio.hpp

@@ -9,18 +9,19 @@
 #ifndef Audio_hpp
 #define Audio_hpp
 
+#include <atomic>
+#include <cstdint>
+
 #include "DMADevice.hpp"
 #include "../../ClockReceiver/ClockReceiver.hpp"
 #include "../../Concurrency/AsyncTaskQueue.hpp"
+#include "../../Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
 
 namespace Amiga {
 
 class Audio: public DMADevice<4> {
 	public:
-		Audio(
-			Chipset &chipset, uint16_t *ram, size_t word_size,
-			[[maybe_unused]] double output_rate) :
-			DMADevice<4>(chipset, ram, word_size) {}
+		Audio(Chipset &chipset, uint16_t *ram, size_t word_size, float output_rate);
 
 		/// Idiomatic call-in for DMA scheduling; indicates that this class may
 		/// perform a DMA access for the stated channel now.
@@ -56,6 +57,11 @@ class Audio: public DMADevice<4> {
 		/// Sets which interrupt requests are currently active.
 		void set_interrupt_requests(uint16_t);
 
+		/// Obtains the output source.
+		Outputs::Speaker::Speaker *get_speaker() {
+			return &speaker_;
+		}
+
 	private:
 		struct Channel {
 			// The data latch plus a count of unused samples
@@ -98,6 +104,16 @@ class Audio: public DMADevice<4> {
 			template <State state> bool output();
 			template <State begin, State end> bool transit();
 		} channels_[4];
+
+		// Transient output state, and its destination.
+		Outputs::Speaker::PushLowpass<true> speaker_;
+		Concurrency::AsyncTaskQueue queue_;
+
+		using AudioBuffer = std::array<int16_t, 4096>;
+		static constexpr int BufferCount = 3;
+		AudioBuffer buffer_[BufferCount];
+		std::atomic<bool> buffer_available_[BufferCount];
+		size_t buffer_pointer_ = 0, sample_pointer_ = 0;
 };
 
 }

Machines/Amiga/Chipset.cpp

@@ -45,7 +45,7 @@ Chipset::Chipset(MemoryMap &map, int input_clock_rate) :
 	},
 	bitplanes_(DMA_CONSTRUCT),
 	copper_(DMA_CONSTRUCT),
-	audio_(DMA_CONSTRUCT, input_clock_rate),
+	audio_(DMA_CONSTRUCT, float(input_clock_rate / 2.0)),
 	crt_(908, 4, Outputs::Display::Type::PAL50, Outputs::Display::InputDataType::Red4Green4Blue4),
 	cia_a_handler_(map, disk_controller_, mouse_),
 	cia_b_handler_(disk_controller_),

Machines/Amiga/Chipset.hpp

@@ -115,6 +115,11 @@ class Chipset: private ClockingHint::Observer {
 		// Input for receiving collected bitplanes.
 		void post_bitplanes(const BitplaneData &data);
 
+		// Obtains the source of audio output.
+		Outputs::Speaker::Speaker *get_speaker() {
+			return audio_.get_speaker();
+		}
+
 	private:
 		friend class DMADeviceBase;