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alsa: implement timing callback

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This commit is contained in:
Robin Gareus 2015-03-05 01:33:13 +01:00
parent 1acbd7c488
commit 782dd70875
2 changed files with 40 additions and 1 deletions
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38
libs/backends/alsa/alsa_audiobackend.cc
View File

@ -50,6 +50,8 @@ AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
, _freewheel (false)
, _freewheeling (false)
, _measure_latency (false)
, _last_process_start (0)
, _process_speed_samples_per_ms (0)
, _audio_device("")
, _midi_driver_option(_("None"))
, _device_reservation(0)
@ -500,6 +502,13 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
_ports.clear();
}
/* reset internal state */
_dsp_load = 0;
_freewheeling = false;
_freewheel = false;
_last_process_start = 0;
_process_speed_samples_per_ms = 0;
release_device();
assert(_rmidi_in.size() == 0);
@ -696,7 +705,25 @@ AlsaAudioBackend::sample_time_at_cycle_start ()
pframes_t
AlsaAudioBackend::samples_since_cycle_start ()
{
return 0;
if (!_active || !_run || _freewheeling || _freewheel) {
return 0;
}
if (_last_process_start == 0 || _process_speed_samples_per_ms) {
return 0;
}
const int64_t elapsed_time_us = _last_process_start - g_get_monotonic_time();
const int64_t nomial_time = 1e6 * _samples_per_period / _samplerate;
assert(elapsed_time_us >=0);
/* linear extrapolation, using [low pass] filtered process-speed. */
const pframes_t processed_samples = elapsed_time_us * _process_speed_samples_per_ms * 1e-3;
if (processed_samples >= _samples_per_period) {
return _samples_per_period;
}
return processed_samples;
}
@ -1465,6 +1492,8 @@ AlsaAudioBackend::main_process_thread ()
memset ((*it)->get_buffer (_samples_per_period), 0, _samples_per_period * sizeof (Sample));
}
/* call engine process callback */
_last_process_start = g_get_monotonic_time();
if (engine.process_callback (_samples_per_period)) {
_pcmi->pcm_stop ();
_active = false;
@ -1504,6 +1533,12 @@ AlsaAudioBackend::main_process_thread ()
clock2 = g_get_monotonic_time();
const int64_t elapsed_time = clock2 - clock1;
_dsp_load = elapsed_time / (float) nomial_time;
const double ps = 1e3 * _samples_per_period / elapsed_time;
// low pass filter, The time-constant should really be
// 1.0 - e^(-2.0 * π * v / SR);
// with v = _samples_per_period / N, and SR = _samples_per_period;
_process_speed_samples_per_ms = _process_speed_samples_per_ms + .05 * (ps - _process_speed_samples_per_ms) + 1e-12;
}
if (xrun && (_pcmi->capt_xrun() > 0 || _pcmi->play_xrun() > 0)) {
@ -1539,6 +1574,7 @@ AlsaAudioBackend::main_process_thread ()
rm->sync_time (clock1);
}
_last_process_start = -1;
if (engine.process_callback (_samples_per_period)) {
_pcmi->pcm_stop ();
_active = false;

3
libs/backends/alsa/alsa_audiobackend.h
View File

@ -305,6 +305,9 @@ class AlsaAudioBackend : public AudioBackend {
bool _freewheeling;
bool _measure_latency;
uint64_t _last_process_start;
double _process_speed_samples_per_ms;
static std::vector<std::string> _midi_options;
static std::vector<AudioBackend::DeviceStatus> _audio_device_status;
static std::vector<AudioBackend::DeviceStatus> _midi_device_status;