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Use sample source to simplify stretching AY.

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This commit is contained in:
Thomas Harte 2024-02-13 22:38:18 -05:00
parent 7f84d5ac6f
commit 27059233b3
1 changed files with 30 additions and 64 deletions
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94
Machines/Apple/AppleII/AppleII.cpp
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@ -15,6 +15,7 @@
#include "../../../Processors/6502/6502.hpp"
#include "../../../Components/AudioToggle/AudioToggle.hpp"
#include "../../../Components/AY38910/AY38910.hpp"
#include "../../../Outputs/Speaker/Implementation/LowpassSpeaker.hpp"
#include "../../../Outputs/Log.hpp"
@ -58,79 +59,44 @@ constexpr int MockingboardSlot = 4; // Conventional Mockingboard slot.
// * ... and hence seven pixels per memory access window clock in high-res mode, 14 in double high-res, etc.
constexpr float master_clock = 14318180.0;
/// Provides an audio source with will hold an instance of @c SourceT for audio generation, repeating one of its output samples
/// after every @c PacketClocks of output.
template <typename SourceT, std::size_t PacketClocks = 456>
class StretchedAudioSource {
public:
template <typename... Args>
StretchedAudioSource(Args &&... args) : source_(std::forward<Args>(args)...) {}
/// Provides an AY that runs at the CPU rate divided by 4 given an input of the master clock divided by 2,
/// allowing for stretched CPU clock cycles.
struct StretchedAY:
public GI::AY38910::AY38910SampleSource<false>,
public Outputs::Speaker::BufferSource<StretchedAY, false> {
void get_samples(std::size_t number_of_samples, int16_t *target) {
// Possible: the sample to duplicate fell exactly at the end of the last batch.
if(!remaining_packet_) {
remaining_packet_ = PacketClocks;
if constexpr (source_.get_is_stero()) {
target[0] = carry[0];
target[1] = carry[1];
target += 2;
} else {
target[0] = carry[0];
++target;
}
--number_of_samples;
}
template <Outputs::Speaker::Action action>
void apply_samples(std::size_t number_of_samples, Outputs::Speaker::MonoSample *target) {
// Divide required input into groups of PacketClocks samples; get all of those
// from the underlying source and then duplicate the final one.
// (1) take 64 windows of 7 input cycles followed by one window of 8 input cycles;
// (2) after each four windows, advance the underlying AY.
//
// Duplicating into the current output packet won't be possible if it happens
// to line up exactly with the end of the PacketClocks, in which case hold a copy
// of the last level output in `carry` until next time.
while(number_of_samples) {
const auto target_length = std::min(number_of_samples, remaining_packet_);
source_.get_samples(target_length, target);
// i.e. advance after:
//
// * 28 cycles, {16 times, then 15 times, then 15 times, then 15 times};
// * 29 cycles, once.
//
// so:
// 16, 1; 15, 1; 15, 1; 15, 1
//
// i.e. add an extra one on the 17th, 33rd, 49th and 65th ticks in a 65-tick loop.
for(std::size_t c = 0; c < number_of_samples; c++) {
++subdivider_;
if(subdivider_ == 28) {
++phase_;
subdivider_ = (phase_ & 15) ? 0 : -1;
if(phase_ == 65) phase_ = 0;
target += target_length * (1 + source_.get_is_stero());
number_of_samples -= target_length;
remaining_packet_ -= target_length;
if(!remaining_packet_) {
if(number_of_samples) {
remaining_packet_ = PacketClocks;
if constexpr (source_.get_is_stero()) {
target[0] = target[-2];
target[1] = target[-1];
target += 2;
} else {
target[0] = target[-1];
++target;
}
} else {
if constexpr (source_.get_is_stero()) {
carry[0] = target[-2];
carry[1] = target[-1];
} else {
carry[0] = target[-1];
}
}
advance();
}
target[c] = level();
}
}
// Direct passthroughs.
void set_sample_volume_range(std::int16_t range) {
source_.set_sample_volume_range(range);
}
bool is_zero_level() const { return source_.is_zero_level(); }
static constexpr bool get_is_stereo() { return SourceT::get_is_stereo(); }
private:
SourceT source_;
std::size_t remaining_packet_ = PacketClocks;
std::array<uint16_t, 2> carry;
int phase_ = 0;
int subdivider_ = 0;
};
}