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ALSA: fix buffer size / period size configuration #917

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ALSA: fix buffer size / period size configuration #917

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21 changes: 11 additions & 10 deletions src/host/alsa/mod.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1061,18 +1061,19 @@ fn set_hw_params_from_format(
hw_params.set_rate(config.sample_rate.0, alsa::ValueOr::Nearest)?;
hw_params.set_channels(config.channels as u32)?;

match config.buffer_size {
BufferSize::Fixed(v) => {
hw_params.set_period_size_near((v / 4) as alsa::pcm::Frames, alsa::ValueOr::Nearest)?;
hw_params.set_buffer_size(v as alsa::pcm::Frames)?;
}
let period_size = match config.buffer_size {
BufferSize::Fixed(v) => v as alsa::pcm::Frames,
BufferSize::Default => {
// These values together represent a moderate latency and wakeup interval.
// Without them, we are at the mercy of the device
hw_params.set_period_time_near(25_000, alsa::ValueOr::Nearest)?;
hw_params.set_buffer_time_near(100_000, alsa::ValueOr::Nearest)?;
// This value represent a moderate latency and wakeup interval.
Comment on lines +1065 to +1067
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Copilot AI Jul 30, 2025

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The Fixed buffer size case is treating the buffer size as period size directly, but according to the PR description and ALSA documentation, buffer size should be nperiod * period_size. For 2 periods, the period size should be v / 2, not v.

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1024 as alsa::pcm::Frames
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Copilot AI Jul 30, 2025

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[nitpick] The explicit cast as alsa::pcm::Frames is unnecessary here since 1024 can be directly assigned to the alsa::pcm::Frames type. Consider using just 1024.

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1024 as alsa::pcm::Frames
1024

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}
}
};
hw_params.set_period_size_near(period_size, alsa::ValueOr::Nearest)?;

// We shouldn't fail if the driver isn't happy here.
// `default` pcm sometimes fails here, but there no reason to as we
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Grammar error: 'there no reason' should be 'there is no reason' or 'there's no reason'.

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// `default` pcm sometimes fails here, but there no reason to as we
// `default` pcm sometimes fails here, but there's no reason to as we

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// provide a direction and 2 is strictly the minimum number of periods.
let _ = hw_params.set_periods(2, alsa::ValueOr::Greater);

pcm_handle.hw_params(&hw_params)?;

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