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record_play_mixer: smoothen time-window allocation

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This patch modifies the mixer's time window allocation by modelling the
drift of the period length over time. This yields a much better
stability of the detected sample rates in the presence of jitter.

Issue #5132
This commit is contained in:
Norman Feske 2024-03-01 15:07:17 +01:00 committed by Christian Helmuth
parent 6407f8667f
commit 913196e2dc
2 changed files with 54 additions and 21 deletions
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2
repos/gems/run/waveform_player.run
View File

@ -104,7 +104,7 @@ install_config {
<resource name="RAM" quantum="2M"/>
<binary name="record_play_mixer"/>
<provides> <service name="Record"/> <service name="Play"/> </provides>
<config jitter_ms="} [jitter_ms] {">
<config jitter_ms="} [jitter_ms] {" record_period_ms="} [record_period_ms] {">
<mix name="left"> <play label_suffix="left"/> </mix>
<mix name="right"> <play label_suffix="right"/> </mix>

73
repos/os/src/server/record_play_mixer/time_window_scheduler.h
View File

@ -44,7 +44,6 @@ class Mixer::Time_window_scheduler
{
unsigned rate_hz;
unsigned median_period_us;
unsigned predicted_now_us;
unsigned jitter_us;
bool valid() const { return median_period_us > 0u; }
@ -53,7 +52,6 @@ class Mixer::Time_window_scheduler
{
Genode::print(out, "rate_hz=", rate_hz,
" median_period_us=", median_period_us,
" predicted_now_us=", predicted_now_us,
" jitter_us=", jitter_us);
}
};
@ -67,7 +65,8 @@ class Mixer::Time_window_scheduler
unsigned _curr_index = 0;
unsigned _num_entries = 0;
unsigned _learned_jitter_us = 5000;
unsigned _learned_jitter_us = 0;
unsigned _learned_period_us = 0;
void _with_nth_entry(unsigned n, auto const &fn) const
{
@ -89,8 +88,7 @@ class Mixer::Time_window_scheduler
unsigned sum_period_us = 0,
num_periods = 0;
unsigned long sum_ages_us = 0, /* relative to latest */
sum_samples = 0;
unsigned long sum_samples = 0;
Entry latest { };
_with_nth_entry(0, [&] (Entry const e) { latest = e; });
@ -104,7 +102,6 @@ class Mixer::Time_window_scheduler
median_period_us.capture(period_us);
num_periods++;
sum_ages_us += latest.time.us_since(prev.time);
sum_period_us += period_us;
sum_samples += prev.num_samples;
});
@ -112,29 +109,35 @@ class Mixer::Time_window_scheduler
if (num_periods == 0)
return { };
unsigned const avg_age_us = unsigned(sum_ages_us/num_periods);
return {
.rate_hz = (sum_period_us == 0) ? 0
: unsigned((sum_samples*1000*1000)/sum_period_us),
.median_period_us = median_period_us.median(),
.predicted_now_us = latest.time.before_us(avg_age_us)
.after_us(sum_period_us/2).us(),
.jitter_us = median_period_us.jitter(),
};
}
void _learn_jitter(Stats const &stats)
void _learn_jitter(Stats const &stats, Config const &config)
{
if (_learned_jitter_us == 0)
_learned_jitter_us = config.jitter_us;
_learned_jitter_us = (99*_learned_jitter_us)/100;
if (stats.jitter_us > _learned_jitter_us)
_learned_jitter_us = stats.jitter_us;
}
void _learn_period(Stats const &stats, Config const &config)
{
if (_learned_period_us == 0)
_learned_period_us = config.period_us;
_learned_period_us = (99*_learned_period_us + stats.median_period_us)/100;
}
/*
* Compute delay on account to the (pre-)fetching the four probe
* values. Noticeable with extremely low sample rates and large
@ -150,6 +153,25 @@ class Mixer::Time_window_scheduler
return (4*sample_distance_ns)/1000;
}
/**
* Return clock value between expected and measured, skewed towards expected
*/
static Clock _counter_drifted(Clock const expected, Clock const measured)
{
auto diff_us = [&] (Clock const &a, Clock const &b)
{
return a.later_than(b) ? a.us_since(b) : b.us_since(a);
};
unsigned const drift_us = diff_us(expected, measured);
unsigned const counter_drift_us = drift_us/20;
if (expected.later_than(measured))
return expected.before_us(counter_drift_us);
else
return expected.after_us(counter_drift_us);
}
public:
Time_window_scheduler() { }
@ -192,13 +214,19 @@ class Mixer::Time_window_scheduler
Stats const stats = _calc_stats();
_learn_jitter(stats);
_learn_jitter(stats, config);
_learn_period(stats, config);
Entry const now = _entries[_curr_index];
unsigned const jitter_us = max(_learned_jitter_us, config.jitter_us);
unsigned const delay_us = jitter_us + _prefetch_us(stats.rate_hz);
Clock const start { previous.end },
end { stats.predicted_now_us + stats.median_period_us + delay_us };
Clock const start { previous.end };
Clock const real_end { now.time.us() + _learned_period_us + delay_us };
Clock const ideal_end { previous.end + _learned_period_us };
Clock const end = _counter_drifted(ideal_end, real_end);
if (Clock::range_valid(start, end))
return Play::Time_window { start.us(), end.us() };
@ -226,12 +254,18 @@ class Mixer::Time_window_scheduler
Stats const stats = _calc_stats();
_learn_jitter(stats);
_learn_jitter(stats, config);
_learn_period(stats, config);
Entry const now = _entries[_curr_index];
unsigned const jitter_us = max(_learned_jitter_us, config.jitter_us);
Clock const start { previous.end },
end { Clock{stats.predicted_now_us}.before_us(jitter_us).us() };
Clock const start { previous.end };
Clock const real_end { now.time.before_us(jitter_us).us() };
Clock const ideal_end { previous.end + _learned_period_us };
Clock const end = _counter_drifted(ideal_end, real_end);
if (Clock::range_valid(start, end))
return Record::Time_window { start.us(), end.us() };
@ -244,8 +278,7 @@ class Mixer::Time_window_scheduler
Stats const stats = _calc_stats();
Genode::print(out, "now=", _entries[_curr_index].time.us()/1000,
" (predicted ", stats.predicted_now_us/1000, ")"
" period=", float(stats.median_period_us)/1000.0f,
" (period=", float(stats.median_period_us)/1000.0f,
" jitter=", float(stats.jitter_us)/1000.0f,
" (learned ", float(_learned_jitter_us)/1000.0f, ")",
" prefetch=", float(_prefetch_us(stats.rate_hz))/1000.0f);