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Merge pull request #1449 from TomHarte/FullerAudio
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Switch to full-clock PWM audio implementation, with noise generator.
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@TomHarte
TomHarte authored Jan 9, 2025
2 parents 8219bee + e1ae65b commit 58ef91a
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Showing 2 changed files with 84 additions and 48 deletions.
120 changes: 76 additions & 44 deletions Machines/Commodore/Plus4/Audio.hpp
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Original file line number Diff line number Diff line change
Expand Up @@ -13,101 +13,133 @@

namespace Commodore::Plus4 {

// PAL: / 160 i.e. 5*32
// NTSC: / 128 i.e. 4*32

// 111860.78125 = NTSC
// 110840.46875 = PAL

class Audio: public Outputs::Speaker::BufferSource<Audio, false> {
public:
Audio(Concurrency::AsyncTaskQueue<false> &audio_queue) :
audio_queue_(audio_queue) {}

template <Outputs::Speaker::Action action>
void apply_samples(std::size_t size, Outputs::Speaker::MonoSample *const target) {
const auto count_frequency = [&](int index) {
++counts_[index];
if(counts_[index] == (frequencies_[index] ^ 1023) * frequency_multiplier_) {
states_[index] ^= 1;
counts_[index] = 0;
} else if(counts_[index] == 1024 * frequency_multiplier_) {
counts_[index] = 0;
// Divide by frequency_multiplier_ and multiply by 8 to get the "8Mhz clock".
// Each 32-window cycle of that clock is a single complete tick of the audio engine.

const auto update_channel = [&](int channel) {
if(sound_dc_ || channels_[channel].count == 0x3ff) {
channels_[channel].count = (channels_[channel].frequency + 1) & 0x3ff;
} else {
++channels_[channel].count;
if(channels_[channel].count == 0x3ff) {
channels_[channel].state ^= 1;
}
}

channels_[channel].pwm_count = 0;
};

if(sound_dc_) {
Outputs::Speaker::fill<action>(target, target + size, Outputs::Speaker::MonoSample(volume_ * 2));
} else {
// TODO: noise generation.
const auto update_noise = [&] {
noise_ <<= 1;
noise_ |= 1 ^ (noise_ >> 7) ^ (noise_ >> 5) ^ (noise_ >> 4) ^ (noise_ >> 1);
};

for(size_t c = 0; c < size; c++) {
count_frequency(0);
count_frequency(1);
for(size_t c = 0; c < size; c++) {
subcycle_ = (subcycle_ + 1) & 31;

Outputs::Speaker::apply<action>(
target[c],
Outputs::Speaker::MonoSample(
(
((states_[0] & masks_[0]) * external_volume_) +
((states_[1] & masks_[1]) * external_volume_)
) * volume_
));
if(subcycle_ == 0) update_channel(0);
if(subcycle_ == 16) {
update_channel(1);
update_noise();
}

++ channels_[0].pwm_count;
++ channels_[1].pwm_count;

if(sound_dc_) {
channels_[0].state = 0;
channels_[1].state = 0;
noise_ = 0;
}

target[c] =
external_volume_ * (
((channels_[0].pwm_count < volume_) & channels_[0].enabled & ~channels_[0].state) |
((channels_[1].pwm_count < volume_) &
(
(channels_[1].enabled & ~channels_[1].state) |
(sound2_noise_on_ & noise_ & 1)
)
)
);
}
r_ += size;
}

void set_sample_volume_range(const std::int16_t range) {
external_volume_ = range / (2 * 9); // Two channels and nine output levels.
external_volume_ = range; // / (2 * 9); // Two channels and nine output levels.
}

bool is_zero_level() const {
return !(masks_[0] || masks_[1] || sound2_noise_on_) || !volume_;
return !(channels_[0].enabled || channels_[1].enabled || sound2_noise_on_) || !volume_;
}

template <int channel> void set_frequency_low(uint8_t value) {
audio_queue_.enqueue([this, value] {
frequencies_[channel] = (frequencies_[channel] & 0xff00) | value;
channels_[channel].frequency = (channels_[channel].frequency & 0xff00) | value;
});
}

template <int channel> void set_frequency_high(uint8_t value) {
audio_queue_.enqueue([this, value] {
frequencies_[channel] = (frequencies_[channel] & 0x00ff) | ((value&3) << 8);
channels_[channel].frequency = (channels_[channel].frequency & 0x00ff) | ((value&3) << 8);
});
}

void set_constrol(uint8_t value) {
void set_control(const uint8_t value) {
audio_queue_.enqueue([this, value] {
switch(value & 0xf) {
case 0: volume_ = 31; break;
case 1: volume_ = 30; break;
case 2: volume_ = 28; break;
case 3: volume_ = 26; break;
case 4: volume_ = 24; break;
case 5: volume_ = 22; break;
case 6: volume_ = 20; break;
case 7: volume_ = 18; break;
default: volume_ = 16; break;
}
volume_ = std::min(value & 0xf, 8); // Only nine volumes are available.
masks_[0] = (value & 0x10) ? 1 : 0;

masks_[1] = (value & 0x20) ? 1 : 0;
channels_[0].enabled = (value & 0x10) ? 1 : 0;
channels_[1].enabled = (value & 0x20) ? 1 : 0;
sound2_noise_on_ = (value & 0x40) && !(value & 0x20);

sound_dc_ = value & 0x80;
});
}

void set_divider(const uint8_t value) {
audio_queue_.enqueue([this, value] {
frequency_multiplier_ = 32 * (value & 0x40 ? 4 : 5);
});
}

private:
// Calling-thread state.
Concurrency::AsyncTaskQueue<false> &audio_queue_;

// Audio-thread state.
int16_t external_volume_ = 0;
int frequencies_[2]{};
int frequency_multiplier_ = 5;
int counts_[2]{};

int states_[2]{};
int masks_[2]{};
int subcycle_ = 0;
struct Channel {
int frequency = 0;
int count = 0;
int pwm_count = 0;
int state = 0;
int enabled = 0;
} channels_[2];
uint8_t noise_ = 0;

bool sound2_noise_on_ = false;
bool sound_dc_ = false;
int volume_ = 0;

int r_ = 0;
};

}
12 changes: 8 additions & 4 deletions Machines/Commodore/Plus4/Plus4.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -146,7 +146,7 @@ class ConcreteMachine:
const auto clock = clock_rate(false);
media_divider_ = Cycles(clock);
set_clock_rate(clock);
speaker_.set_input_rate(float(clock) / 32.0f);
speaker_.set_input_rate(float(clock));

// TODO: decide whether to attach a 1541 for real.
const bool has_c1541 = true;
Expand Down Expand Up @@ -347,7 +347,11 @@ class ConcreteMachine:
case 0xff04: timers_.write<4>(*value); break;
case 0xff05: timers_.write<5>(*value); break;
case 0xff06: video_.write<0xff06>(*value); break;
case 0xff07: video_.write<0xff07>(*value); break;
case 0xff07:
video_.write<0xff07>(*value);
update_audio();
audio_.set_divider(*value);
break;
case 0xff08:
// Observation here: the kernel posts a 0 to this
// address upon completing each keyboard scan cycle,
Expand Down Expand Up @@ -398,7 +402,7 @@ class ConcreteMachine:
case 0xff11:
ff11_ = *value;
update_audio();
audio_.set_constrol(*value);
audio_.set_control(*value);
break;
case 0xff12:
ff12_ = *value & 0x3f;
Expand Down Expand Up @@ -540,7 +544,7 @@ class ConcreteMachine:
Cycles time_since_audio_update_;
Outputs::Speaker::PullLowpass<Audio> speaker_;
void update_audio() {
speaker_.run_for(audio_queue_, time_since_audio_update_.divide(Cycles(32)));
speaker_.run_for(audio_queue_, time_since_audio_update_.flush<Cycles>());
}

// MARK: - MappedKeyboardMachine.
Expand Down

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