CLK/Machines/Amiga/Audio.hpp

//
//  Audio.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 09/11/2021.
//  Copyright © 2021 Thomas Harte. All rights reserved.
//

#pragma once

#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, float output_rate);

	/// Idiomatic call-in for DMA scheduling; indicates that this class may
	/// perform a DMA access for the stated channel now.
	bool advance_dma(int channel);

	/// Advances output by one DMA window, which is implicitly two cycles
	/// at the output rate that was specified to the constructor.
	void output();

	/// Sets the total number of words to fetch for the given channel.
	void set_length(int channel, uint16_t);

	/// Sets the number of DMA windows between each 8-bit output,
	/// in the same time base as @c ticks_per_line.
	void set_period(int channel, uint16_t);

	/// Sets the output volume for the given channel; if bit 6 is set
	/// then output is maximal; otherwise bits 0–5 select
	/// a volume of [0–63]/64, on a logarithmic scale.
	void set_volume(int channel, uint16_t);

	/// Sets the next two samples of audio to output.
	template <bool is_external = true> void set_data(int channel, uint16_t);

	/// Provides a copy of the DMA enable flags, for the purpose of
	/// determining which channels are enabled for DMA.
	void set_channel_enables(uint16_t);

	/// Sets which channels, if any, modulate period or volume of
	/// their neighbours.
	void set_modulation_flags(uint16_t);

	/// 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
		// in the latch, which will always be 0, 1 or 2.
		uint16_t data = 0x0000;
		bool wants_data = false;
		uint16_t data_latch = 0x0000;

		// The DMA address; unlike most of the Amiga Chipset,
		// the user posts a value to feed a pointer, rather
		// than having access to the pointer itself.
		bool should_reload_address = false;
		uint32_t data_address = 0x0000'0000;

		// Number of words remaining in DMA data.
		uint16_t length = 0;
		uint16_t length_counter = 0;

		// Number of ticks between each sample, plus the
		// current counter, which counts downward.
		uint16_t period = 0;
		uint16_t period_counter = 0;

		// Modulation / attach flags.
		bool attach_period = false;
		bool attach_volume = false;

		// Output volume, [0, 64].
		uint8_t volume = 0;
		uint8_t volume_latch = 0;

		// Indicates whether DMA is enabled for this channel.
		bool dma_enabled = false;

		// Records whether this audio interrupt is pending.
		bool interrupt_pending = false;
		bool will_request_interrupt = false;

		// Replicates the Hardware Reference Manual state machine;
		// comments indicate which of the documented states each
		// label refers to.
		enum class State {
			Disabled,			// 000
			WaitingForDummyDMA,	// 001
			WaitingForDMA,		// 101
			PlayingHigh,		// 010
			PlayingLow,			// 011
		} state = State::Disabled;

		/// Dispatches to the appropriate templatised output for the current state.
		/// @param moduland The channel to modulate, if modulation is enabled.
		/// @returns @c true if an interrupt should be posted; @c false otherwise.
		bool output(Channel *moduland);

		/// Applies dynamic logic for @c state, mostly testing for potential state transitions.
		/// @param moduland The channel to modulate, if modulation is enabled.
		/// @returns @c true if an interrupt should be posted; @c false otherwise.
		template <State state> bool output(Channel *moduland);

		/// Transitions from @c begin to @c end, calling the appropriate @c begin_state
		/// and taking any steps specific to that particular transition.
		/// @param moduland The channel to modulate, if modulation is enabled.
		/// @returns @c true if an interrupt should be posted; @c false otherwise.
		template <State begin, State end> bool transit(Channel *moduland);

		/// Begins @c state, performing all fixed logic that would otherwise have to be
		/// repeated endlessly in the relevant @c output.
		/// @param moduland The channel to modulate, if modulation is enabled.
		template <State state> void begin_state(Channel *moduland);

		/// Provides the common length-decrementing logic used when transitioning
		/// between PlayingHigh and PlayingLow in either direction.
		void decrement_length();

		// Output state.
		int8_t output_level = 0;
		uint8_t output_phase = 0;
		bool output_enabled = false;

		void reset_output_phase() {
			output_phase = 0;
			output_enabled = (volume_latch > 0) && !attach_period && !attach_volume;
		}
	} channels_[4];

	// Transient output state, and its destination.
	Outputs::Speaker::PushLowpass<true> speaker_;
	Concurrency::AsyncTaskQueue<true> 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;
};

}