ALSA: fix thinko in sample time calc.

1 files changed, 3 insertions, 20 deletions

diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 8befb9219c..cc0054bd68 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -51,7 +51,6 @@ AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
 	, _freewheeling (false)
 	, _measure_latency (false)
 	, _last_process_start (0)
-	, _process_speed_samples_per_ms (0)
 	, _audio_device("")
 	, _midi_driver_option(_("None"))
 	, _device_reservation(0)
@@ -510,7 +509,6 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 	_freewheeling = false;
 	_freewheel = false;
 	_last_process_start = 0;
-	_process_speed_samples_per_ms = 0;
 
 	release_device();
 
@@ -711,21 +709,12 @@ AlsaAudioBackend::samples_since_cycle_start ()
 	if (!_active || !_run || _freewheeling || _freewheel) {
 		return 0;
 	}
-	if (_last_process_start == 0 || _process_speed_samples_per_ms) {
+	if (_last_process_start == 0) {
 		return 0;
 	}
 
-	const int64_t elapsed_time_us = _last_process_start - g_get_monotonic_time();
-
-	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;
+	const int64_t elapsed_time_us = g_get_monotonic_time() - _last_process_start;
+	return std::max((pframes_t)0, (pframes_t)rint(1e-6 * elapsed_time_us * _samplerate));
 }
 
 
@@ -1551,12 +1540,6 @@ 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)) {