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103 lines
3.4 KiB
C++
103 lines
3.4 KiB
C++
//
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// Audio.cpp
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// Clock Signal
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//
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// Created by Thomas Harte on 31/05/2019.
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// Copyright © 2019 Thomas Harte. All rights reserved.
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//
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#include "Audio.hpp"
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using namespace Apple::Macintosh;
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namespace {
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const std::size_t sample_length = 352;
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}
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Audio::Audio(Concurrency::DeferringAsyncTaskQueue &task_queue) : task_queue_(task_queue) {}
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// MARK: - Inputs
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void Audio::post_sample(uint8_t sample) {
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// Grab the read and write pointers, ensure there's room for a new sample and, if not,
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// drop this one.
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const auto write_pointer = sample_queue_.write_pointer.load();
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const auto read_pointer = sample_queue_.read_pointer.load();
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const decltype(write_pointer) next_write_pointer = (write_pointer + 1) % sample_queue_.buffer.size();
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if(next_write_pointer == read_pointer) {
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return;
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}
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sample_queue_.buffer[write_pointer] = sample;
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sample_queue_.write_pointer.store(next_write_pointer);
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}
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void Audio::set_volume(int volume) {
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// Post the volume change as a deferred event.
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task_queue_.defer([=] () {
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volume_ = volume;
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});
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}
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void Audio::set_enabled(bool on) {
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// Post the enabled mask change as a deferred event.
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task_queue_.defer([=] () {
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enabled_mask_ = on ? 1 : 0;
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});
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}
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// MARK: - Output generation
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bool Audio::is_zero_level() {
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return !volume_ || !enabled_mask_;
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}
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void Audio::set_sample_volume_range(std::int16_t range) {
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// Some underflow here doesn't really matter.
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volume_multiplier_ = range / (7 * 255);
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}
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void Audio::get_samples(std::size_t number_of_samples, int16_t *target) {
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const auto write_pointer = sample_queue_.write_pointer.load();
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auto read_pointer = sample_queue_.read_pointer.load();
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// TODO: the implementation below acts as if the hardware uses pulse-amplitude modulation;
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// in fact it uses pulse-width modulation. But the scale for pulses isn't specified, so
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// that's something to return to.
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// TODO: temporary implementation. Very inefficient. Replace.
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for(std::size_t sample = 0; sample < number_of_samples; ++sample) {
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target[sample] = volume_multiplier_ * int16_t(sample_queue_.buffer[read_pointer] * volume_ * enabled_mask_);
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++subcycle_offset_;
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if(subcycle_offset_ == sample_length) {
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// printf("%d: %d\n", sample_queue_.buffer[read_pointer], volume_multiplier_ * int16_t(sample_queue_.buffer[read_pointer]));
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subcycle_offset_ = 0;
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const unsigned int next_read_pointer = (read_pointer + 1) % sample_queue_.buffer.size();
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if(next_read_pointer != write_pointer) {
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read_pointer = next_read_pointer;
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}
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}
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}
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sample_queue_.read_pointer.store(read_pointer);
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}
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void Audio::skip_samples(std::size_t number_of_samples) {
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const auto write_pointer = sample_queue_.write_pointer.load();
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auto read_pointer = sample_queue_.read_pointer.load();
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// Number of samples that would be consumed is (number_of_samples + subcycle_offset_) / sample_length.
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const unsigned int samples_passed = static_cast<unsigned int>((number_of_samples + subcycle_offset_) / sample_length);
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subcycle_offset_ = (number_of_samples + subcycle_offset_) % sample_length;
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// Get also number of samples available.
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const unsigned int samples_available = static_cast<unsigned int>((write_pointer + sample_queue_.buffer.size() - read_pointer) % sample_queue_.buffer.size());
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// Advance by whichever of those is the lower number.
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const auto samples_to_consume = std::min(samples_available, samples_passed);
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read_pointer = (read_pointer + samples_to_consume) % sample_queue_.buffer.size();
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sample_queue_.read_pointer.store(read_pointer);
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}
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