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Optimize the additive DAC code, fixing performance-related hangs #21662

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Sep 25, 2023
Merged

Optimize the additive DAC code, fixing performance-related hangs #21662

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36d2f85
Optimize the additive DAC code, fixing performance-related hangs
Nebuleon Jul 31, 2023
a20c6eb
Address linter failure in the previous commit
Nebuleon Aug 1, 2023
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15 changes: 9 additions & 6 deletions platforms/chibios/drivers/audio_dac_additive.c
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Original file line number Diff line number Diff line change
Expand Up @@ -121,24 +121,27 @@ __attribute__((weak)) uint16_t dac_value_generate(void) {
/* doing additive wave synthesis over all currently playing tones = adding up
* sine-wave-samples for each frequency, scaled by the number of active tones
*/
uint16_t value = 0;
float frequency = 0.0f;
uint_fast16_t value = 0;
float frequency = 0.0f;

for (uint8_t i = 0; i < active_tones_snapshot_length; i++) {
for (size_t i = 0; i < active_tones_snapshot_length; i++) {
/* Note: a user implementation does not have to rely on the active_tones_snapshot, but
* could directly query the active frequencies through audio_get_processed_frequency */
frequency = active_tones_snapshot[i];

dac_if[i] = dac_if[i] + ((frequency * AUDIO_DAC_BUFFER_SIZE) / AUDIO_DAC_SAMPLE_RATE) * 2 / 3;
float new_dac_if = dac_if[i];
new_dac_if += frequency * ((float)AUDIO_DAC_BUFFER_SIZE / AUDIO_DAC_SAMPLE_RATE * 2.0f / 3.0f);
/*Note: the 2/3 are necessary to get the correct frequencies on the
* DAC output (as measured with an oscilloscope), since the gpt
* timer runs with 3*AUDIO_DAC_SAMPLE_RATE; and the DAC callback
* is called twice per conversion.*/

dac_if[i] = fmodf(dac_if[i], AUDIO_DAC_BUFFER_SIZE);
while (new_dac_if >= AUDIO_DAC_BUFFER_SIZE)
new_dac_if -= AUDIO_DAC_BUFFER_SIZE;
dac_if[i] = new_dac_if;

// Wavetable generation/lookup
uint16_t dac_i = (uint16_t)dac_if[i];
size_t dac_i = (size_t)new_dac_if;

#if defined(AUDIO_DAC_SAMPLE_WAVEFORM_SINE)
value += dac_buffer_sine[dac_i] / active_tones_snapshot_length;
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