add 'available' interface to the AudioBackendInfo
[ardour.git] / libs / backends / alsa / alsa_audiobackend.cc
index cec72418a4ce2352260037a8c5003e00ab542a8c..0f7a89eaf246aee4a08741cd6a3c783bf7b13353 100644 (file)
@@ -38,6 +38,9 @@ using namespace ARDOUR;
 
 static std::string s_instance_name;
 size_t AlsaAudioBackend::_max_buffer_size = 8192;
+std::vector<std::string> AlsaAudioBackend::_midi_options;
+std::vector<AudioBackend::DeviceStatus> AlsaAudioBackend::_audio_device_status;
+std::vector<AudioBackend::DeviceStatus> AlsaAudioBackend::_midi_device_status;
 
 AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
        : AudioBackend (e, info)
@@ -45,17 +48,18 @@ AlsaAudioBackend::AlsaAudioBackend (AudioEngine& e, AudioBackendInfo& info)
        , _run (false)
        , _active (false)
        , _freewheeling (false)
+       , _measure_latency (false)
        , _audio_device("")
-       , _midi_device("")
+       , _midi_driver_option(_("None"))
        , _device_reservation(0)
        , _samplerate (48000)
        , _samples_per_period (1024)
        , _periods_per_cycle (2)
-       , _dsp_load (0)
        , _n_inputs (0)
        , _n_outputs (0)
-       , _systemic_input_latency (0)
-       , _systemic_output_latency (0)
+       , _systemic_audio_input_latency (0)
+       , _systemic_audio_output_latency (0)
+       , _dsp_load (0)
        , _processed_samples (0)
        , _port_change_flag (false)
 {
@@ -85,13 +89,14 @@ AlsaAudioBackend::is_realtime () const
 std::vector<AudioBackend::DeviceStatus>
 AlsaAudioBackend::enumerate_devices () const
 {
-       std::vector<AudioBackend::DeviceStatus> s;
+       _audio_device_status.clear();
        std::map<std::string, std::string> devices;
        get_alsa_audio_device_names(devices);
        for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
-               s.push_back (DeviceStatus (i->first, true));
+               if (_audio_device == "") _audio_device = i->first;
+               _audio_device_status.push_back (DeviceStatus (i->first, true));
        }
-       return s;
+       return _audio_device_status;
 }
 
 void
@@ -128,7 +133,7 @@ AlsaAudioBackend::acquire_device(const char* device_name)
        _reservation_succeeded = false;
 
        std::string request_device_exe;
-       if (!PBD::find_file_in_search_path (
+       if (!PBD::find_file (
                                PBD::Searchpath(Glib::build_filename(ARDOUR::ardour_dll_directory(), "ardouralsautil")
                                        + G_SEARCHPATH_SEPARATOR_S + ARDOUR::ardour_dll_directory()),
                                "ardour-request-device", request_device_exe))
@@ -278,14 +283,32 @@ AlsaAudioBackend::set_output_channels (uint32_t cc)
 int
 AlsaAudioBackend::set_systemic_input_latency (uint32_t sl)
 {
-       _systemic_input_latency = sl;
+       _systemic_audio_input_latency = sl;
        return 0;
 }
 
 int
 AlsaAudioBackend::set_systemic_output_latency (uint32_t sl)
 {
-       _systemic_output_latency = sl;
+       _systemic_audio_output_latency = sl;
+       return 0;
+}
+
+int
+AlsaAudioBackend::set_systemic_midi_input_latency (std::string const device, uint32_t sl)
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return -1;
+       nfo->systemic_input_latency = sl;
+       return 0;
+}
+
+int
+AlsaAudioBackend::set_systemic_midi_output_latency (std::string const device, uint32_t sl)
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return -1;
+       nfo->systemic_output_latency = sl;
        return 0;
 }
 
@@ -329,44 +352,119 @@ AlsaAudioBackend::output_channels () const
 uint32_t
 AlsaAudioBackend::systemic_input_latency () const
 {
-       return _systemic_input_latency;
+       return _systemic_audio_input_latency;
 }
 
 uint32_t
 AlsaAudioBackend::systemic_output_latency () const
 {
-       return _systemic_output_latency;
+       return _systemic_audio_output_latency;
+}
+
+uint32_t
+AlsaAudioBackend::systemic_midi_input_latency (std::string const device) const
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return 0;
+       return nfo->systemic_input_latency;
+}
+
+uint32_t
+AlsaAudioBackend::systemic_midi_output_latency (std::string const device) const
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return 0;
+       return nfo->systemic_output_latency;
 }
 
 /* MIDI */
+struct AlsaAudioBackend::AlsaMidiDeviceInfo *
+AlsaAudioBackend::midi_device_info(std::string const name) const {
+       for (std::map<std::string, struct AlsaMidiDeviceInfo*>::const_iterator i = _midi_devices.begin (); i != _midi_devices.end(); ++i) {
+               if (i->first == name) {
+                       return (i->second);
+               }
+       }
+
+       assert(_midi_driver_option != _("None"));
+
+       std::map<std::string, std::string> devices;
+       if (_midi_driver_option == _("ALSA raw devices")) {
+               get_alsa_rawmidi_device_names(devices);
+       } else {
+               get_alsa_sequencer_names (devices);
+       }
+
+       for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
+               if (i->first == name) {
+                       _midi_devices[name] = new AlsaMidiDeviceInfo();
+                       return _midi_devices[name];
+               }
+       }
+       return 0;
+}
+
 std::vector<std::string>
 AlsaAudioBackend::enumerate_midi_options () const
 {
-       std::vector<std::string> m;
-       m.push_back (_("-None-"));
+       if (_midi_options.empty()) {
+               _midi_options.push_back (_("None"));
+               _midi_options.push_back (_("ALSA raw devices"));
+               _midi_options.push_back (_("ALSA sequencer"));
+       }
+       return _midi_options;
+}
+
+std::vector<AudioBackend::DeviceStatus>
+AlsaAudioBackend::enumerate_midi_devices () const
+{
+       _midi_device_status.clear();
        std::map<std::string, std::string> devices;
-       get_alsa_rawmidi_device_names(devices);
 
-       for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
-               m.push_back (i->first);
+       if (_midi_driver_option == _("ALSA raw devices")) {
+               get_alsa_rawmidi_device_names (devices);
        }
-       if (m.size() > 2) {
-               m.push_back (_("-All-"));
+       else if (_midi_driver_option == _("ALSA sequencer")) {
+               get_alsa_sequencer_names (devices);
+       }
+
+       for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
+               _midi_device_status.push_back (DeviceStatus (i->first, true));
        }
-       return m;
+       return _midi_device_status;
 }
 
 int
 AlsaAudioBackend::set_midi_option (const std::string& opt)
 {
-       _midi_device = opt;
+       if (opt != _("None") && opt != _("ALSA raw devices") && opt != _("ALSA sequencer")) {
+               return -1;
+       }
+       _midi_driver_option = opt;
        return 0;
 }
 
 std::string
 AlsaAudioBackend::midi_option () const
 {
-       return _midi_device;
+       return _midi_driver_option;
+}
+
+int
+AlsaAudioBackend::set_midi_device_enabled (std::string const device, bool enable)
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return -1;
+       nfo->enabled = enable;
+       return 0;
+}
+
+bool
+AlsaAudioBackend::midi_device_enabled (std::string const device) const
+{
+       struct AlsaMidiDeviceInfo * nfo = midi_device_info(device);
+       if (!nfo) return false;
+       return nfo->enabled;
 }
 
 /* State Control */
@@ -382,6 +480,11 @@ static void * pthread_process (void *arg)
 int
 AlsaAudioBackend::_start (bool for_latency_measurement)
 {
+       if (!_active && _run) {
+               // recover from 'halted', reap threads
+               stop();
+       }
+
        if (_active || _run) {
                PBD::error << _("AlsaAudioBackend: already active.") << endmsg;
                return -1;
@@ -463,10 +566,7 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
                PBD::warning << _("AlsaAudioBackend: sample rate does not match.") << endmsg;
        }
 
-       if (for_latency_measurement) {
-               _systemic_input_latency = 0;
-               _systemic_output_latency = 0;
-       }
+       _measure_latency = for_latency_measurement;
 
        register_system_midi_ports();
 
@@ -524,7 +624,7 @@ int
 AlsaAudioBackend::stop ()
 {
        void *status;
-       if (!_active) {
+       if (!_run) {
                return 0;
        }
 
@@ -535,19 +635,19 @@ AlsaAudioBackend::stop ()
        }
 
        while (!_rmidi_out.empty ()) {
-               AlsaRawMidiIO *m = _rmidi_out.back ();
+               AlsaMidiIO *m = _rmidi_out.back ();
                m->stop();
                _rmidi_out.pop_back ();
                delete m;
        }
        while (!_rmidi_in.empty ()) {
-               AlsaRawMidiIO *m = _rmidi_in.back ();
+               AlsaMidiIO *m = _rmidi_in.back ();
                m->stop();
                _rmidi_in.pop_back ();
                delete m;
        }
 
-       unregister_system_ports();
+       unregister_ports();
        delete _pcmi; _pcmi = 0;
        release_device();
 
@@ -658,6 +758,10 @@ AlsaAudioBackend::join_process_threads ()
 bool
 AlsaAudioBackend::in_process_thread ()
 {
+       if (pthread_equal (_main_thread, pthread_self()) != 0) {
+               return true;
+       }
+
        for (std::vector<pthread_t>::const_iterator i = _threads.begin (); i != _threads.end (); ++i)
        {
                if (pthread_equal (*i, pthread_self ()) != 0) {
@@ -676,6 +780,8 @@ AlsaAudioBackend::process_thread_count ()
 void
 AlsaAudioBackend::update_latencies ()
 {
+       // trigger latency callback in RT thread (locked graph)
+       port_connect_add_remove_callback();
 }
 
 /* PORTENGINE API */
@@ -813,8 +919,8 @@ AlsaAudioBackend::add_port (
 void
 AlsaAudioBackend::unregister_port (PortEngine::PortHandle port_handle)
 {
-       if (!valid_port (port_handle)) {
-               PBD::error << _("AlsaBackend::unregister_port: Invalid Port.") << endmsg;
+       if (!_run) {
+               return;
        }
        AlsaPort* port = static_cast<AlsaPort*>(port_handle);
        std::vector<AlsaPort*>::iterator i = std::find (_ports.begin (), _ports.end (), static_cast<AlsaPort*>(port_handle));
@@ -836,7 +942,7 @@ AlsaAudioBackend::register_system_audio_ports()
        const int a_out = _n_outputs > 0 ? _n_outputs : 2;
 
        /* audio ports */
-       lr.min = lr.max = _samples_per_period * _periods_per_cycle + _systemic_input_latency;
+       lr.min = lr.max = _samples_per_period + (_measure_latency ? 0 : _systemic_audio_input_latency);
        for (int i = 1; i <= a_ins; ++i) {
                char tmp[64];
                snprintf(tmp, sizeof(tmp), "system:capture_%d", i);
@@ -846,7 +952,7 @@ AlsaAudioBackend::register_system_audio_ports()
                _system_inputs.push_back(static_cast<AlsaPort*>(p));
        }
 
-       lr.min = lr.max = _samples_per_period * _periods_per_cycle + _systemic_output_latency;
+       lr.min = lr.max = _samples_per_period + (_measure_latency ? 0 : _systemic_audio_output_latency);
        for (int i = 1; i <= a_out; ++i) {
                char tmp[64];
                snprintf(tmp, sizeof(tmp), "system:playback_%d", i);
@@ -861,35 +967,33 @@ AlsaAudioBackend::register_system_audio_ports()
 int
 AlsaAudioBackend::register_system_midi_ports()
 {
-       LatencyRange lr;
-       std::vector<std::string> devices;
+       std::map<std::string, std::string> devices;
+       int midi_ins = 0;
+       int midi_outs = 0;
 
-       if (_midi_device == _("-None-")) {
+       if (_midi_driver_option == _("None")) {
                return 0;
-       }
-       else if (_midi_device == _("-All-")) {
-               std::map<std::string, std::string> devmap;
-               get_alsa_rawmidi_device_names(devmap);
-               for (std::map<std::string, std::string>::const_iterator i = devmap.begin (); i != devmap.end(); ++i) {
-                       devices.push_back (i->second);
-               }
+       } else if (_midi_driver_option == _("ALSA raw devices")) {
+               get_alsa_rawmidi_device_names(devices);
        } else {
-               std::map<std::string, std::string> devmap;
-               get_alsa_rawmidi_device_names(devmap);
-               for (std::map<std::string, std::string>::const_iterator i = devmap.begin (); i != devmap.end(); ++i) {
-                       if (i->first == _midi_device) {
-                               devices.push_back (i->second);
-                               break;
-                       }
-               }
+               get_alsa_sequencer_names (devices);
        }
 
-       for (std::vector<std::string>::const_iterator i = devices.begin (); i != devices.end (); ++i) {
+       for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
+               struct AlsaMidiDeviceInfo * nfo = midi_device_info(i->first);
+               if (!nfo) continue;
+               if (!nfo->enabled) continue;
+
+               AlsaMidiOut *mout;
+               if (_midi_driver_option == _("ALSA raw devices")) {
+                       mout = new AlsaRawMidiOut (i->second.c_str());
+               } else {
+                       mout = new AlsaSeqMidiOut (i->second.c_str());
+               }
 
-               AlsaRawMidiOut *mout = new AlsaRawMidiOut (i->c_str());
                if (mout->state ()) {
                        PBD::warning << string_compose (
-                                       _("AlsaRawMidiOut: failed to open midi device '%1'."), *i)
+                                       _("AlsaMidiOut: failed to open midi device '%1'."), i->second)
                                << endmsg;
                        delete mout;
                } else {
@@ -897,18 +1001,36 @@ AlsaAudioBackend::register_system_midi_ports()
                        mout->sync_time (g_get_monotonic_time());
                        if (mout->start ()) {
                                PBD::warning << string_compose (
-                                               _("AlsaRawMidiOut: failed to start midi device '%1'."), *i)
+                                               _("AlsaMidiOut: failed to start midi device '%1'."), i->second)
                                        << endmsg;
                                delete mout;
                        } else {
+                               char tmp[64];
+                               snprintf(tmp, sizeof(tmp), "system:midi_playback_%d", ++midi_ins);
+                               PortHandle p = add_port(std::string(tmp), DataType::MIDI, static_cast<PortFlags>(IsInput | IsPhysical | IsTerminal));
+                               if (!p) {
+                                       mout->stop();
+                                       delete mout;
+                               }
+                               LatencyRange lr;
+                               lr.min = lr.max = _samples_per_period + (_measure_latency ? 0 : nfo->systemic_output_latency);
+                               set_latency_range (p, false, lr);
+                               static_cast<AlsaMidiPort*>(p)->set_n_periods(2);
+                               _system_midi_out.push_back(static_cast<AlsaPort*>(p));
                                _rmidi_out.push_back (mout);
                        }
                }
 
-               AlsaRawMidiIn *midin = new AlsaRawMidiIn (i->c_str());
+               AlsaMidiIn *midin;
+               if (_midi_driver_option == _("ALSA raw devices")) {
+                       midin = new AlsaRawMidiIn (i->second.c_str());
+               } else {
+                       midin = new AlsaSeqMidiIn (i->second.c_str());
+               }
+
                if (midin->state ()) {
                        PBD::warning << string_compose (
-                                       _("AlsaRawMidiIn: failed to open midi device '%1'."), *i)
+                                       _("AlsaMidiIn: failed to open midi device '%1'."), i->second)
                                << endmsg;
                        delete midin;
                } else {
@@ -916,43 +1038,31 @@ AlsaAudioBackend::register_system_midi_ports()
                        midin->sync_time (g_get_monotonic_time());
                        if (midin->start ()) {
                                PBD::warning << string_compose (
-                                               _("AlsaRawMidiIn: failed to start midi device '%1'."), *i)
+                                               _("AlsaMidiIn: failed to start midi device '%1'."), i->second)
                                        << endmsg;
                                delete midin;
                        } else {
+                               char tmp[64];
+                               snprintf(tmp, sizeof(tmp), "system:midi_capture_%d", ++midi_outs);
+                               PortHandle p = add_port(std::string(tmp), DataType::MIDI, static_cast<PortFlags>(IsOutput | IsPhysical | IsTerminal));
+                               if (!p) {
+                                       midin->stop();
+                                       delete midin;
+                                       continue;
+                               }
+                               LatencyRange lr;
+                               lr.min = lr.max = _samples_per_period + (_measure_latency ? 0 : nfo->systemic_input_latency);
+                               set_latency_range (p, false, lr);
+                               _system_midi_in.push_back(static_cast<AlsaPort*>(p));
                                _rmidi_in.push_back (midin);
                        }
                }
        }
-
-       const int m_ins = _rmidi_in.size();
-       const int m_out = _rmidi_out.size();
-
-       lr.min = lr.max = _samples_per_period + _systemic_input_latency;
-       for (int i = 1; i <= m_ins; ++i) {
-               char tmp[64];
-               snprintf(tmp, sizeof(tmp), "system:midi_capture_%d", i);
-               PortHandle p = add_port(std::string(tmp), DataType::MIDI, static_cast<PortFlags>(IsOutput | IsPhysical | IsTerminal));
-               if (!p) return -1;
-               set_latency_range (p, false, lr);
-               _system_midi_in.push_back(static_cast<AlsaPort*>(p));
-       }
-
-       lr.min = lr.max = _samples_per_period + _systemic_output_latency;
-       for (int i = 1; i <= m_out; ++i) {
-               char tmp[64];
-               snprintf(tmp, sizeof(tmp), "system:midi_playback_%d", i);
-               PortHandle p = add_port(std::string(tmp), DataType::MIDI, static_cast<PortFlags>(IsInput | IsPhysical | IsTerminal));
-               if (!p) return -1;
-               set_latency_range (p, true, lr);
-               _system_midi_out.push_back(static_cast<AlsaPort*>(p));
-       }
-
        return 0;
 }
 
 void
-AlsaAudioBackend::unregister_system_ports()
+AlsaAudioBackend::unregister_ports (bool system_only)
 {
        size_t i = 0;
        _system_inputs.clear();
@@ -961,8 +1071,9 @@ AlsaAudioBackend::unregister_system_ports()
        _system_midi_out.clear();
        while (i <  _ports.size ()) {
                AlsaPort* port = _ports[i];
-               if (port->is_physical () && port->is_terminal ()) {
+               if (! system_only || (port->is_physical () && port->is_terminal ())) {
                        port->disconnect_all ();
+                       delete port;
                        _ports.erase (_ports.begin() + i);
                } else {
                        ++i;
@@ -1291,6 +1402,8 @@ AlsaAudioBackend::main_process_thread ()
        clock1 = g_get_monotonic_time();
        _pcmi->pcm_start ();
        int no_proc_errors = 0;
+       const int bailout = 2 * _samplerate / _samples_per_period;
+       const int64_t nomial_time = 1e6 * _samples_per_period / _samplerate;
 
        manager.registration_callback();
        manager.graph_order_callback();
@@ -1305,7 +1418,7 @@ AlsaAudioBackend::main_process_thread ()
                                ++no_proc_errors;
                                xrun = true;
                        }
-                       if (_pcmi->state () < 0 || no_proc_errors > 50) {
+                       if (_pcmi->state () < 0 || no_proc_errors > bailout) {
                                PBD::error << _("AlsaAudioBackend: I/O error. Audio Process Terminated.") << endmsg;
                                break;
                        }
@@ -1324,10 +1437,10 @@ AlsaAudioBackend::main_process_thread ()
                                i = 0;
                                for (std::vector<AlsaPort*>::const_iterator it = _system_midi_in.begin (); it != _system_midi_in.end (); ++it, ++i) {
                                        assert (_rmidi_in.size() > i);
-                                       AlsaRawMidiIn *rm = static_cast<AlsaRawMidiIn*>(_rmidi_in.at(i));
+                                       AlsaMidiIn *rm = _rmidi_in.at(i);
                                        void *bptr = (*it)->get_buffer(0);
                                        pframes_t time;
-                                       uint8_t data[64]; // match MaxAlsaRawEventSize in alsa_rawmidi.cc
+                                       uint8_t data[64]; // match MaxAlsaEventSize in alsa_rawmidi.cc
                                        size_t size = sizeof(data);
                                        midi_clear(bptr);
                                        while (rm->recv_event (time, data, size)) {
@@ -1347,14 +1460,19 @@ AlsaAudioBackend::main_process_thread ()
                                        return 0;
                                }
 
-                               /* queue midi*/
+                               i = 0;
+                               for (std::vector<AlsaPort*>::iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it, ++i) {
+                                       static_cast<AlsaMidiPort*>(*it)->next_period();
+                               }
+
+                               /* queue midi */
                                i = 0;
                                for (std::vector<AlsaPort*>::const_iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it, ++i) {
                                        assert (_rmidi_out.size() > i);
-                                       AlsaRawMidiOut *rm = static_cast<AlsaRawMidiOut*>(_rmidi_out.at(i));
-                                       const AlsaMidiBuffer *src = static_cast<const AlsaMidiBuffer*>((*it)->get_buffer(0));
-                                       rm->sync_time (clock1); // ?? use clock pre DSP load?
-                                       for (AlsaMidiBuffer::const_iterator mit = src->begin (); mit != src->end (); ++mit) {
+                                       const AlsaMidiBuffer src = static_cast<const AlsaMidiPort*>(*it)->const_buffer();
+                                       AlsaMidiOut *rm = _rmidi_out.at(i);
+                                       rm->sync_time (clock1);
+                                       for (AlsaMidiBuffer::const_iterator mit = src.begin (); mit != src.end (); ++mit) {
                                                rm->send_event ((*mit)->timestamp(), (*mit)->data(), (*mit)->size());
                                        }
                                }
@@ -1375,7 +1493,6 @@ AlsaAudioBackend::main_process_thread ()
                                /* calculate DSP load */
                                clock2 = g_get_monotonic_time();
                                const int64_t elapsed_time = clock2 - clock1;
-                               const int64_t nomial_time = 1e6 * _samples_per_period / _samplerate;
                                _dsp_load = elapsed_time / (float) nomial_time;
                        }
 
@@ -1427,6 +1544,10 @@ AlsaAudioBackend::main_process_thread ()
                if (connections_changed) {
                        manager.graph_order_callback();
                }
+               if (connections_changed || ports_changed) {
+                       engine.latency_callback(false);
+                       engine.latency_callback(true);
+               }
 
        }
        _pcmi->pcm_stop ();
@@ -1446,13 +1567,15 @@ static boost::shared_ptr<AudioBackend> backend_factory (AudioEngine& e);
 static int instantiate (const std::string& arg1, const std::string& /* arg2 */);
 static int deinstantiate ();
 static bool already_configured ();
+static bool available ();
 
 static ARDOUR::AudioBackendInfo _descriptor = {
-       "Alsa",
+       "ALSA",
        instantiate,
        deinstantiate,
        backend_factory,
        already_configured,
+       available
 };
 
 static boost::shared_ptr<AudioBackend>
@@ -1484,6 +1607,12 @@ already_configured ()
        return false;
 }
 
+static bool
+available ()
+{
+       return true;
+}
+
 extern "C" ARDOURBACKEND_API ARDOUR::AudioBackendInfo* descriptor ()
 {
        return &_descriptor;
@@ -1652,8 +1781,11 @@ void* AlsaAudioPort::get_buffer (pframes_t n_samples)
 
 AlsaMidiPort::AlsaMidiPort (AlsaAudioBackend &b, const std::string& name, PortFlags flags)
        : AlsaPort (b, name, flags)
+       , _n_periods (1)
+       , _bufperiod (0)
 {
-       _buffer.clear ();
+       _buffer[0].clear ();
+       _buffer[1].clear ();
 }
 
 AlsaMidiPort::~AlsaMidiPort () { }
@@ -1667,18 +1799,18 @@ struct MidiEventSorter {
 void* AlsaMidiPort::get_buffer (pframes_t /* nframes */)
 {
        if (is_input ()) {
-               _buffer.clear ();
+               (_buffer[_bufperiod]).clear ();
                for (std::vector<AlsaPort*>::const_iterator i = get_connections ().begin ();
                                i != get_connections ().end ();
                                ++i) {
                        const AlsaMidiBuffer src = static_cast<const AlsaMidiPort*>(*i)->const_buffer ();
                        for (AlsaMidiBuffer::const_iterator it = src.begin (); it != src.end (); ++it) {
-                               _buffer.push_back (boost::shared_ptr<AlsaMidiEvent>(new AlsaMidiEvent (**it)));
+                               (_buffer[_bufperiod]).push_back (boost::shared_ptr<AlsaMidiEvent>(new AlsaMidiEvent (**it)));
                        }
                }
-               std::sort (_buffer.begin (), _buffer.end (), MidiEventSorter());
+               std::sort ((_buffer[_bufperiod]).begin (), (_buffer[_bufperiod]).end (), MidiEventSorter());
        }
-       return &_buffer;
+       return &(_buffer[_bufperiod]);
 }
 
 AlsaMidiEvent::AlsaMidiEvent (const pframes_t timestamp, const uint8_t* data, size_t size)