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CLK/Machines/Amiga/Audio.hpp

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//
// Audio.hpp
// Clock Signal
//
// Created by Thomas Harte on 09/11/2021.
// Copyright © 2021 Thomas Harte. All rights reserved.
//
#pragma once
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#include <atomic>
#include <cstdint>
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#include "DMADevice.hpp"
#include "../../ClockReceiver/ClockReceiver.hpp"
#include "../../Concurrency/AsyncTaskQueue.hpp"
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#include "../../Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
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namespace Amiga {
class Audio: public DMADevice<4> {
public:
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Audio(Chipset &chipset, uint16_t *ram, size_t word_size, float output_rate);
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/// 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);
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/// 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 05 select
/// a volume of [063]/64, on a logarithmic scale.
void set_volume(int channel, uint16_t);
/// Sets the next two samples of audio to output.
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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);
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/// 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;
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// 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;
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// Modulation / attach flags.
bool attach_period = false;
bool attach_volume = false;
// Output volume, [0, 64].
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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;
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/// Dispatches to the appropriate templatised output for the current state.
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/// @param moduland The channel to modulate, if modulation is enabled.
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/// @returns @c true if an interrupt should be posted; @c false otherwise.
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bool output(Channel *moduland);
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/// Applies dynamic logic for @c state, mostly testing for potential state transitions.
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/// @param moduland The channel to modulate, if modulation is enabled.
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/// @returns @c true if an interrupt should be posted; @c false otherwise.
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template <State state> bool output(Channel *moduland);
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/// Transitions from @c begin to @c end, calling the appropriate @c begin_state
/// and taking any steps specific to that particular transition.
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/// @param moduland The channel to modulate, if modulation is enabled.
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/// @returns @c true if an interrupt should be posted; @c false otherwise.
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template <State begin, State end> bool transit(Channel *moduland);
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/// Begins @c state, performing all fixed logic that would otherwise have to be
/// repeated endlessly in the relevant @c output.
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/// @param moduland The channel to modulate, if modulation is enabled.
template <State state> void begin_state(Channel *moduland);
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/// Provides the common length-decrementing logic used when transitioning
/// between PlayingHigh and PlayingLow in either direction.
void decrement_length();
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// Output state.
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int8_t output_level = 0;
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uint8_t output_phase = 0;
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bool output_enabled = false;
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void reset_output_phase() {
output_phase = 0;
output_enabled = (volume_latch > 0) && !attach_period && !attach_volume;
}
} channels_[4];
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// Transient output state, and its destination.
Outputs::Speaker::PushLowpass<true> speaker_;
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Concurrency::AsyncTaskQueue<true> queue_;
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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;
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};
}