implement ALSA period/cycle setting

2 files changed, 38 insertions, 3 deletions

diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index b0997a6202..d0236327f3 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -330,6 +330,15 @@ AlsaAudioBackend::available_output_channel_count (const std::string& device) con
 	return 128;
 }
 
+std::vector<uint32_t>
+AlsaAudioBackend::available_period_sizes (const std::string& driver) const
+{
+	std::vector<uint32_t> ps;
+	ps.push_back (2);
+	ps.push_back (3);
+	return ps;
+}
+
 bool
 AlsaAudioBackend::can_change_sample_rate_when_running () const
 {
@@ -423,6 +432,19 @@ AlsaAudioBackend::set_sample_rate (float sr)
 }
 
 int
+AlsaAudioBackend::set_peridod_size (uint32_t n)
+{
+	if (n == 0 || n > 3) {
+		return -1;
+	}
+	if (_run) {
+		return -1;
+	}
+	_periods_per_cycle = n;
+	return 0;
+}
+
+int
 AlsaAudioBackend::set_buffer_size (uint32_t bs)
 {
 	if (bs <= 0 || bs >= _max_buffer_size) {
@@ -526,6 +548,12 @@ AlsaAudioBackend::buffer_size () const
 	return _samples_per_period;
 }
 
+uint32_t
+AlsaAudioBackend::period_size () const
+{
+	return _periods_per_cycle;
+}
+
 bool
 AlsaAudioBackend::interleaved () const
 {
@@ -1208,6 +1236,8 @@ AlsaAudioBackend::register_system_audio_ports()
 	const int a_ins = _n_inputs;
 	const int a_out = _n_outputs;
 
+	// TODO set latency depending on _periods_per_cycle and  _samples_per_period
+
 	/* audio ports */
 	lr.min = lr.max = (_measure_latency ? 0 : _systemic_audio_input_latency);
 	for (int i = 1; i <= a_ins; ++i) {
@@ -1282,7 +1312,7 @@ AlsaAudioBackend::register_system_midi_ports()
 				LatencyRange lr;
 				lr.min = lr.max = (_measure_latency ? 0 : nfo->systemic_output_latency);
 				set_latency_range (p, false, lr);
-				static_cast<AlsaMidiPort*>(p)->set_n_periods(2);
+				static_cast<AlsaMidiPort*>(p)->set_n_periods(_periods_per_cycle); // TODO check MIDI alignment
 				_system_midi_out.push_back(static_cast<AlsaPort*>(p));
 				_rmidi_out.push_back (mout);
 			}
diff --git a/libs/backends/alsa/alsa_audiobackend.h b/libs/backends/alsa/alsa_audiobackend.h
index c95593c349..1dca7ec149 100644
--- a/libs/backends/alsa/alsa_audiobackend.h
+++ b/libs/backends/alsa/alsa_audiobackend.h
@@ -148,10 +148,10 @@ class AlsaMidiPort : public AlsaPort {
 		const AlsaMidiBuffer * const_buffer () const { return & _buffer[_bufperiod]; }
 
 		void next_period() { if (_n_periods > 1) { get_buffer(0); _bufperiod = (_bufperiod + 1) % _n_periods; } }
-		void set_n_periods(int n) { if (n > 0 && n < 3) { _n_periods = n; } }
+		void set_n_periods(int n) { if (n > 0 && n < 4) { _n_periods = n; } }
 
 	private:
-		AlsaMidiBuffer _buffer[2];
+		AlsaMidiBuffer _buffer[3];
 		int _n_periods;
 		int _bufperiod;
 }; // class AlsaMidiPort
@@ -168,6 +168,8 @@ class AlsaAudioBackend : public AudioBackend {
 		bool is_realtime () const;
 
 		bool use_separate_input_and_output_devices () const { return true; }
+		bool can_set_period_size () const { return true; }
+
 		std::vector<DeviceStatus> enumerate_devices () const;
 		std::vector<DeviceStatus> enumerate_input_devices () const;
 		std::vector<DeviceStatus> enumerate_output_devices () const;
@@ -175,6 +177,7 @@ class AlsaAudioBackend : public AudioBackend {
 		std::vector<float> available_sample_rates2 (const std::string&, const std::string&) const;
 		std::vector<uint32_t> available_buffer_sizes (const std::string& device) const;
 		std::vector<uint32_t> available_buffer_sizes2 (const std::string&, const std::string&) const;
+		std::vector<uint32_t> available_period_sizes (const std::string& driver) const;
 		uint32_t available_input_channel_count (const std::string& device) const;
 		uint32_t available_output_channel_count (const std::string& device) const;
 
@@ -186,6 +189,7 @@ class AlsaAudioBackend : public AudioBackend {
 		int set_output_device_name (const std::string&);
 		int set_sample_rate (float);
 		int set_buffer_size (uint32_t);
+		int set_peridod_size (uint32_t);
 		int set_interleaved (bool yn);
 		int set_input_channels (uint32_t);
 		int set_output_channels (uint32_t);
@@ -202,6 +206,7 @@ class AlsaAudioBackend : public AudioBackend {
 		std::string  output_device_name () const;
 		float        sample_rate () const;
 		uint32_t     buffer_size () const;
+		uint32_t     period_size () const;
 		bool         interleaved () const;
 		uint32_t     input_channels () const;
 		uint32_t     output_channels () const;