CLK/Machines/Acorn/Archimedes/Sound.hpp

//
//  Audio.hpp
//  Clock Signal
//
//  Created by Thomas Harte on 20/03/2024.
//  Copyright © 2024 Thomas Harte. All rights reserved.
//

#pragma once

#include <cstdint>

namespace Archimedes {

/// Models the Archimedes sound output; in a real machine this is a joint efort between the VIDC and the MEMC.
template <typename InterruptObserverT>
struct Sound {
	Sound(InterruptObserverT &observer, const uint8_t *ram) : ram_(ram), observer_(observer) {}

	void set_next_end(uint32_t value) {
		next_.end = value;
	}

	void set_next_start(uint32_t value) {
		next_.start = value;
		set_buffer_valid(true);	// My guess: this is triggered on next buffer start write.
	}

	bool interrupt() const {
		return !next_buffer_valid_;
	}

	void swap() {
		current_.start = next_.start;
		std::swap(current_.end, next_.end);
		set_buffer_valid(false);
		set_halted(false);
	}

	void set_frequency(uint8_t frequency) {
		divider_ = reload_ = frequency;
	}

	void set_stereo_image(uint8_t channel, uint8_t value) {
		if(!value) {
			positions_[channel].left =
			positions_[channel].right = 0;
			return;
		}

		positions_[channel].right = value - 1;
		positions_[channel].left = 6 - positions_[channel].right;
	}

	void tick() {
		// Do nothing if not currently outputting.
		if(halted_) {
			return;
		}

		// Apply user-programmed clock divider.
		--divider_;
		if(divider_) return;
		divider_ = reload_;

		// Grab a single byte from the FIFO.
		// TODO: and convert to a linear value, apply stereo image, output.
		++byte_;

		// If the FIFO is exhausted, consider triggering a DMA request.
		if(byte_ == 16) {
			byte_ = 0;

			current_.start += 16;
			if(current_.start == current_.end) {
				if(next_buffer_valid_) {
					swap();
				} else {
					set_halted(true);
				}
			}
		}
	}

private:
	const uint8_t *ram_ = nullptr;

	uint8_t divider_ = 0, reload_ = 0;
	int byte_ = 0;

	void set_buffer_valid(bool valid) {
		next_buffer_valid_ = valid;
		observer_.update_interrupts();
	}

	void set_halted(bool halted) {
		if(halted_ != halted && !halted) {
			byte_ = 0;
			divider_ = reload_;
		}
		halted_ = halted;
	}

	bool next_buffer_valid_ = false;
	bool halted_ = true;				// This is a bit of a guess.

	struct Buffer {
		uint32_t start = 0, end = 0;
	};
	Buffer current_, next_;

	struct StereoPosition {
		// These are maintained as sixths, i.e. a value of 6 means 100%.
		int left, right;
	} positions_[8];

	InterruptObserverT &observer_;
};

}