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Sets up a queue to push memory writes onto the audio thread.

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This commit is contained in:
Thomas Harte 2020-11-18 21:40:56 -05:00
parent a7051e4e42
commit 4b9fe805e9
2 changed files with 79 additions and 14 deletions
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57
Machines/Apple/AppleIIgs/Sound.cpp
View File

@ -10,14 +10,25 @@
#include <cstdio>
// TODO: is it safe not to check for back-pressure in pending_stores_?
using namespace Apple::IIgs::Sound;
GLU::GLU(Concurrency::DeferringAsyncTaskQueue &audio_queue) : audio_queue_(audio_queue) {}
void GLU::set_data(uint8_t data) {
if(control_ & 0x40) {
if(local_.control & 0x40) {
// RAM access.
local_.ram_[address_] = data;
MemoryWrite write;
write.enabled = true;
write.address = address_;
write.value = data;
write.time = pending_store_write_time_;
pending_stores_[pending_store_write_].store(write, std::memory_order::memory_order_release);
pending_store_write_ = (pending_store_write_ + 1) % (StoreBufferSize - 1);
} else {
// Register access.
switch(address_ & 0xe0) {
@ -31,7 +42,7 @@ void GLU::set_data(uint8_t data) {
// printf("Register write %04x\n", address_);
}
if(control_ & 0x20) {
if(local_.control & 0x20) {
++address_;
}
}
@ -44,17 +55,34 @@ uint8_t GLU::get_data() {
void GLU::run_for(Cycles cycles) {
// Update local state, without generating audio.
local_.skip_audio(cycles.as<size_t>());
skip_audio(local_, cycles.as<size_t>());
// Update the timestamp for memory writes;
pending_store_write_time_ += cycles.as<uint32_t>();
}
void GLU::get_samples(std::size_t number_of_samples, std::int16_t *target) {
// Update remote state, generating audio.
remote_.generate_audio(number_of_samples, target, output_range_);
generate_audio(number_of_samples, target, output_range_);
}
void GLU::skip_samples(const std::size_t number_of_samples) {
// Update remote state, without generating audio.
remote_.skip_audio(number_of_samples);
skip_audio(remote_, number_of_samples);
// Apply any pending stores.
std::atomic_thread_fence(std::memory_order::memory_order_acquire);
const uint32_t final_time = pending_store_read_time_ + uint32_t(number_of_samples);
while(true) {
auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
if(!next_store.enabled) break;
if(next_store.time >= final_time) break;
remote_.ram_[next_store.address] = next_store.value;
next_store.enabled = false;
pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);
pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
}
}
void GLU::set_sample_volume_range(std::int16_t range) {
@ -92,16 +120,29 @@ uint8_t GLU::get_address_high() {
// MARK: - Update logic.
void GLU::EnsoniqState::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t range) {
void GLU::generate_audio(size_t number_of_samples, std::int16_t *target, int16_t range) {
(void)number_of_samples;
(void)target;
(void)range;
memset(target, 0, number_of_samples * sizeof(int16_t));
auto next_store = pending_stores_[pending_store_read_].load(std::memory_order::memory_order_acquire);
for(size_t c = 0; c < number_of_samples; c++) {
target[c] = 0;
// Apply any RAM writes that interleave here.
++pending_store_read_time_;
if(!next_store.enabled) continue;
if(next_store.time != pending_store_read_time_) continue;
remote_.ram_[next_store.address] = next_store.value;
next_store.enabled = false;
pending_stores_[pending_store_read_].store(next_store, std::memory_order::memory_order_relaxed);
pending_store_read_ = (pending_store_read_ + 1) & (StoreBufferSize - 1);
}
}
void GLU::EnsoniqState::skip_audio(size_t number_of_samples) {
void GLU::skip_audio(EnsoniqState &state, size_t number_of_samples) {
(void)number_of_samples;
(void)state;
// Just advance all oscillator pointers and check for interrupts.
// If a read occurs to the current-output level, generate it then.

36
Machines/Apple/AppleIIgs/Sound.hpp
View File

@ -9,6 +9,8 @@
#ifndef Apple_IIgs_Sound_hpp
#define Apple_IIgs_Sound_hpp
#include <atomic>
#include "../../../ClockReceiver/ClockReceiver.hpp"
#include "../../../Concurrency/AsyncTaskQueue.hpp"
#include "../../../Outputs/Speaker/Implementation/SampleSource.hpp"
@ -42,6 +44,26 @@ class GLU: public Outputs::Speaker::SampleSource {
uint16_t address_ = 0;
// Use a circular buffer for piping memory alterations onto the audio
// thread; it would be prohibitive to defer every write individually.
//
// Assumed: on most modern architectures, an atomic 64-bit read or
// write can be achieved locklessly.
struct MemoryWrite {
uint32_t time;
uint16_t address;
uint8_t value;
bool enabled = false;
};
static_assert(sizeof(MemoryWrite) == 8);
constexpr static int StoreBufferSize = 16384;
std::atomic<MemoryWrite> pending_stores_[StoreBufferSize];
uint32_t pending_store_read_ = 0, pending_store_read_time_ = 0;
uint32_t pending_store_write_ = 0, pending_store_write_time_ = 0;
// Maintain state both 'locally' (i.e. on the emulation thread) and
// 'remotely' (i.e. on the audio thread).
struct EnsoniqState {
uint8_t ram_[65536];
struct Oscillator {
@ -55,16 +77,18 @@ class GLU: public Outputs::Speaker::SampleSource {
uint8_t table_size;
} oscillators_[32];
// TODO: do all of these need to be on the audio thread?
uint8_t control;
void generate_audio(size_t number_of_samples, std::int16_t *target, int16_t range);
void skip_audio(size_t number_of_samples);
uint8_t interrupt_state;
uint8_t oscillator_enable;
} local_, remote_;
uint8_t interrupt_state_;
uint8_t oscillator_enable_;
uint8_t control_ = 0x00;
// Functions to update an EnsoniqState; these don't belong to the state itself
// because they also access the pending stores (inter alia).
void generate_audio(size_t number_of_samples, std::int16_t *target, int16_t range);
void skip_audio(EnsoniqState &state, size_t number_of_samples);
// Audio-thread state.
int16_t output_range_ = 0;
};