call me Mr. Backend

simple blocking (no callback) PortAudio Backend

6 files changed, 2615 insertions, 0 deletions

diff --git a/libs/backends/portaudio/portaudio_backend.cc b/libs/backends/portaudio/portaudio_backend.cc
new file mode 100644
index 0000000000..f94c819b22
--- /dev/null
+++ b/libs/backends/portaudio/portaudio_backend.cc
@@ -0,0 +1,1557 @@
+/*
+ * Copyright (C) 2015-2015 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2013 Paul Davis
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <regex.h>
+
+#ifndef PLATFORM_WINDOWS
+#include <sys/mman.h>
+#include <sys/time.h>
+#endif
+
+#include <glibmm.h>
+
+#include "portaudio_backend.h"
+#include "rt_thread.h"
+
+#include "pbd/compose.h"
+#include "pbd/error.h"
+#include "pbd/file_utils.h"
+#include "ardour/filesystem_paths.h"
+#include "ardour/port_manager.h"
+#include "i18n.h"
+
+using namespace ARDOUR;
+
+static std::string s_instance_name;
+size_t PortAudioBackend::_max_buffer_size = 8192;
+std::vector<std::string> PortAudioBackend::_midi_options;
+std::vector<AudioBackend::DeviceStatus> PortAudioBackend::_audio_device_status;
+
+PortAudioBackend::PortAudioBackend (AudioEngine& e, AudioBackendInfo& info)
+	: AudioBackend (e, info)
+	, _pcmio (0)
+	, _run (false)
+	, _active (false)
+	, _freewheel (false)
+	, _measure_latency (false)
+	, _last_process_start (0)
+	, _audio_device("")
+	, _midi_driver_option(_("None"))
+	, _samplerate (48000)
+	, _samples_per_period (1024)
+	, _n_inputs (0)
+	, _n_outputs (0)
+	, _systemic_audio_input_latency (0)
+	, _systemic_audio_output_latency (0)
+	, _dsp_load (0)
+	, _processed_samples (0)
+	, _port_change_flag (false)
+{
+	_instance_name = s_instance_name;
+	pthread_mutex_init (&_port_callback_mutex, 0);
+
+	_pcmio = new PortAudioIO ();
+}
+
+PortAudioBackend::~PortAudioBackend ()
+{
+	delete _pcmio; _pcmio = 0;
+	pthread_mutex_destroy (&_port_callback_mutex);
+}
+
+/* AUDIOBACKEND API */
+
+std::string
+PortAudioBackend::name () const
+{
+	return X_("PortAudio");
+}
+
+bool
+PortAudioBackend::is_realtime () const
+{
+	return true;
+}
+
+std::vector<AudioBackend::DeviceStatus>
+PortAudioBackend::enumerate_devices () const
+{
+	_pcmio->discover();
+	_audio_device_status.clear();
+	std::map<int, std::string> devices;
+	_pcmio->device_list(devices);
+
+	for (std::map<int, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
+		if (_audio_device == "") _audio_device = i->second;
+		_audio_device_status.push_back (DeviceStatus (i->second, true));
+	}
+	return _audio_device_status;
+}
+
+std::vector<float>
+PortAudioBackend::available_sample_rates (const std::string&) const
+{
+	std::vector<float> sr;
+	_pcmio->available_sample_rates(name_to_id(_audio_device), sr);
+	return sr;
+}
+
+std::vector<uint32_t>
+PortAudioBackend::available_buffer_sizes (const std::string&) const
+{
+	std::vector<uint32_t> bs;
+	_pcmio->available_buffer_sizes(name_to_id(_audio_device), bs);
+	return bs;
+}
+
+uint32_t
+PortAudioBackend::available_input_channel_count (const std::string&) const
+{
+	return 128; // TODO query current device
+}
+
+uint32_t
+PortAudioBackend::available_output_channel_count (const std::string&) const
+{
+	return 128; // TODO query current device
+}
+
+bool
+PortAudioBackend::can_change_sample_rate_when_running () const
+{
+	return false;
+}
+
+bool
+PortAudioBackend::can_change_buffer_size_when_running () const
+{
+	return false; // TODO
+}
+
+int
+PortAudioBackend::set_device_name (const std::string& d)
+{
+	_audio_device = d;
+	return 0;
+}
+
+int
+PortAudioBackend::set_sample_rate (float sr)
+{
+	if (sr <= 0) { return -1; }
+	// TODO check if it's in the list of valid SR
+	_samplerate = sr;
+	engine.sample_rate_change (sr);
+	return 0;
+}
+
+int
+PortAudioBackend::set_buffer_size (uint32_t bs)
+{
+	if (bs <= 0 || bs >= _max_buffer_size) {
+		return -1;
+	}
+	_samples_per_period = bs;
+	engine.buffer_size_change (bs);
+	return 0;
+}
+
+int
+PortAudioBackend::set_interleaved (bool yn)
+{
+	if (!yn) { return 0; }
+	return -1;
+}
+
+int
+PortAudioBackend::set_input_channels (uint32_t cc)
+{
+	_n_inputs = cc;
+	return 0;
+}
+
+int
+PortAudioBackend::set_output_channels (uint32_t cc)
+{
+	_n_outputs = cc;
+	return 0;
+}
+
+int
+PortAudioBackend::set_systemic_input_latency (uint32_t sl)
+{
+	_systemic_audio_input_latency = sl;
+	return 0;
+}
+
+int
+PortAudioBackend::set_systemic_output_latency (uint32_t sl)
+{
+	_systemic_audio_output_latency = sl;
+	return 0;
+}
+
+/* Retrieving parameters */
+std::string
+PortAudioBackend::device_name () const
+{
+	return _audio_device;
+}
+
+float
+PortAudioBackend::sample_rate () const
+{
+	return _samplerate;
+}
+
+uint32_t
+PortAudioBackend::buffer_size () const
+{
+	return _samples_per_period;
+}
+
+bool
+PortAudioBackend::interleaved () const
+{
+	return false;
+}
+
+uint32_t
+PortAudioBackend::input_channels () const
+{
+	return _n_inputs;
+}
+
+uint32_t
+PortAudioBackend::output_channels () const
+{
+	return _n_outputs;
+}
+
+uint32_t
+PortAudioBackend::systemic_input_latency () const
+{
+	return _systemic_audio_input_latency;
+}
+
+uint32_t
+PortAudioBackend::systemic_output_latency () const
+{
+	return _systemic_audio_output_latency;
+}
+
+/* MIDI */
+
+std::vector<std::string>
+PortAudioBackend::enumerate_midi_options () const
+{
+	if (_midi_options.empty()) {
+		//_midi_options.push_back (_("PortMidi"));
+		_midi_options.push_back (_("None"));
+	}
+	return _midi_options;
+}
+
+int
+PortAudioBackend::set_midi_option (const std::string& opt)
+{
+	if (opt != _("None") /* && opt != _("PortMidi")*/) {
+		return -1;
+	}
+	_midi_driver_option = opt;
+	return 0;
+}
+
+std::string
+PortAudioBackend::midi_option () const
+{
+	return _midi_driver_option;
+}
+
+/* State Control */
+
+static void * pthread_process (void *arg)
+{
+	PortAudioBackend *d = static_cast<PortAudioBackend *>(arg);
+	d->main_process_thread ();
+	pthread_exit (0);
+	return 0;
+}
+
+int
+PortAudioBackend::_start (bool for_latency_measurement)
+{
+	if (!_active && _run) {
+		// recover from 'halted', reap threads
+		stop();
+	}
+
+	if (_active || _run) {
+		PBD::error << _("PortAudioBackend: already active.") << endmsg;
+		return -1;
+	}
+
+	if (_ports.size()) {
+		PBD::warning << _("PortAudioBackend: recovering from unclean shutdown, port registry is not empty.") << endmsg;
+		_system_inputs.clear();
+		_system_outputs.clear();
+		_system_midi_in.clear();
+		_system_midi_out.clear();
+		_ports.clear();
+	}
+
+	/* reset internal state */
+	_dsp_load = 0;
+	_freewheeling = false;
+	_freewheel = false;
+	_last_process_start = 0;
+
+	_pcmio->pcm_setup (name_to_id(_audio_device), name_to_id(_audio_device), _samplerate, _samples_per_period);
+
+	switch (_pcmio->state ()) {
+		case 0: /* OK */ break;
+		case -1: PBD::error << _("PortAudioBackend: failed to open device.") << endmsg; break;
+		default: PBD::error << _("PortAudioBackend: initialization failed.") << endmsg; break;
+	}
+	if (_pcmio->state ()) {
+		return -1;
+	}
+
+	if (_n_outputs != _pcmio->n_playback_channels ()) {
+		_n_outputs = _pcmio->n_playback_channels ();
+		PBD::info << _("PortAudioBackend: adjusted output channel count to match device.") << endmsg;
+	}
+
+	if (_n_inputs != _pcmio->n_capture_channels ()) {
+		_n_inputs = _pcmio->n_capture_channels ();
+		PBD::info << _("PortAudioBackend: adjusted input channel count to match device.") << endmsg;
+	}
+#if 0
+	if (_pcmio->samples_per_period() != _samples_per_period) {
+		_samples_per_period = _pcmio->samples_per_period();
+		PBD::warning << _("PortAudioBackend: samples per period does not match.") << endmsg;
+	}
+#endif
+
+	if (_pcmio->sample_rate() != _samplerate) {
+		_samplerate = _pcmio->sample_rate();
+		engine.sample_rate_change (_samplerate);
+		PBD::warning << _("PortAudioBackend: sample rate does not match.") << endmsg;
+	}
+
+	_measure_latency = for_latency_measurement;
+
+	_run = true;
+	_port_change_flag = false;
+
+	// TODO MIDI
+
+	if (register_system_audio_ports()) {
+		PBD::error << _("PortAudioBackend: failed to register system ports.") << endmsg;
+		_run = false;
+		return -1;
+	}
+
+	engine.sample_rate_change (_samplerate);
+	engine.buffer_size_change (_samples_per_period);
+
+	if (engine.reestablish_ports ()) {
+		PBD::error << _("PortAudioBackend: Could not re-establish ports.") << endmsg;
+		_run = false;
+		return -1;
+	}
+
+	engine.reconnect_ports ();
+	_run = true;
+	_port_change_flag = false;
+
+	if (_realtime_pthread_create (SCHED_FIFO, -20, 100000,
+				&_main_thread, pthread_process, this))
+	{
+		if (pthread_create (&_main_thread, NULL, pthread_process, this))
+		{
+			PBD::error << _("PortAudioBackend: failed to create process thread.") << endmsg;
+			_run = false;
+			return -1;
+		} else {
+			PBD::warning << _("PortAudioBackend: cannot acquire realtime permissions.") << endmsg;
+		}
+	}
+
+	int timeout = 5000;
+	while (!_active && --timeout > 0) { Glib::usleep (1000); }
+
+	if (timeout == 0 || !_active) {
+		PBD::error << _("PortAudioBackend: failed to start.") << endmsg;
+		_pcmio->pcm_stop();
+		_run = false;
+		unregister_ports();
+		_active = false;
+		return -1;
+	}
+
+	return 0;
+}
+
+int
+PortAudioBackend::stop ()
+{
+	void *status;
+	if (!_run) {
+		return 0;
+	}
+
+	_run = false;
+	if (pthread_join (_main_thread, &status)) {
+		PBD::error << _("PortAudioBackend: failed to terminate.") << endmsg;
+		return -1;
+	}
+
+
+	unregister_ports();
+
+	return (_active == false) ? 0 : -1;
+}
+
+int
+PortAudioBackend::freewheel (bool onoff)
+{
+	if (onoff == _freewheeling) {
+		return 0;
+	}
+	_freewheeling = onoff;
+	return 0;
+}
+
+float
+PortAudioBackend::dsp_load () const
+{
+	return 100.f * _dsp_load;
+}
+
+size_t
+PortAudioBackend::raw_buffer_size (DataType t)
+{
+	switch (t) {
+		case DataType::AUDIO:
+			return _samples_per_period * sizeof(Sample);
+		case DataType::MIDI:
+			return _max_buffer_size; // XXX not really limited
+	}
+	return 0;
+}
+
+/* Process time */
+framepos_t
+PortAudioBackend::sample_time ()
+{
+	return _processed_samples;
+}
+
+framepos_t
+PortAudioBackend::sample_time_at_cycle_start ()
+{
+	return _processed_samples;
+}
+
+pframes_t
+PortAudioBackend::samples_since_cycle_start ()
+{
+	if (!_active || !_run || _freewheeling || _freewheel) {
+		return 0;
+	}
+	if (_last_process_start == 0) {
+		return 0;
+	}
+
+	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));
+}
+
+int
+PortAudioBackend::name_to_id(std::string device_name) const {
+	uint32_t device_id = UINT32_MAX;
+	std::map<int, std::string> devices;
+	_pcmio->device_list(devices);
+
+	for (std::map<int, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
+		if (i->second == device_name) {
+			device_id = i->first;
+			break;
+		}
+	}
+	return device_id;
+}
+
+void *
+PortAudioBackend::portaudio_process_thread (void *arg)
+{
+	ThreadData* td = reinterpret_cast<ThreadData*> (arg);
+	boost::function<void ()> f = td->f;
+	delete td;
+	f ();
+	return 0;
+}
+
+int
+PortAudioBackend::create_process_thread (boost::function<void()> func)
+{
+	pthread_t thread_id;
+	pthread_attr_t attr;
+	size_t stacksize = 100000;
+
+	ThreadData* td = new ThreadData (this, func, stacksize);
+
+	if (_realtime_pthread_create (SCHED_FIFO, -21, stacksize,
+				&thread_id, portaudio_process_thread, td)) {
+		pthread_attr_init (&attr);
+		pthread_attr_setstacksize (&attr, stacksize);
+		if (pthread_create (&thread_id, &attr, portaudio_process_thread, td)) {
+			PBD::error << _("AudioEngine: cannot create process thread.") << endmsg;
+			pthread_attr_destroy (&attr);
+			return -1;
+		}
+		pthread_attr_destroy (&attr);
+	}
+
+	_threads.push_back (thread_id);
+	return 0;
+}
+
+int
+PortAudioBackend::join_process_threads ()
+{
+	int rv = 0;
+
+	for (std::vector<pthread_t>::const_iterator i = _threads.begin (); i != _threads.end (); ++i)
+	{
+		void *status;
+		if (pthread_join (*i, &status)) {
+			PBD::error << _("AudioEngine: cannot terminate process thread.") << endmsg;
+			rv -= 1;
+		}
+	}
+	_threads.clear ();
+	return rv;
+}
+
+bool
+PortAudioBackend::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) {
+			return true;
+		}
+	}
+	return false;
+}
+
+uint32_t
+PortAudioBackend::process_thread_count ()
+{
+	return _threads.size ();
+}
+
+void
+PortAudioBackend::update_latencies ()
+{
+	// trigger latency callback in RT thread (locked graph)
+	port_connect_add_remove_callback();
+}
+
+/* PORTENGINE API */
+
+void*
+PortAudioBackend::private_handle () const
+{
+	return NULL;
+}
+
+const std::string&
+PortAudioBackend::my_name () const
+{
+	return _instance_name;
+}
+
+bool
+PortAudioBackend::available () const
+{
+	return _run && _active;
+}
+
+uint32_t
+PortAudioBackend::port_name_size () const
+{
+	return 256;
+}
+
+int
+PortAudioBackend::set_port_name (PortEngine::PortHandle port, const std::string& name)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::set_port_name: Invalid Port(s)") << endmsg;
+		return -1;
+	}
+	return static_cast<PamPort*>(port)->set_name (_instance_name + ":" + name);
+}
+
+std::string
+PortAudioBackend::get_port_name (PortEngine::PortHandle port) const
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::get_port_name: Invalid Port(s)") << endmsg;
+		return std::string ();
+	}
+	return static_cast<PamPort*>(port)->name ();
+}
+
+PortEngine::PortHandle
+PortAudioBackend::get_port_by_name (const std::string& name) const
+{
+	PortHandle port = (PortHandle) find_port (name);
+	return port;
+}
+
+int
+PortAudioBackend::get_ports (
+		const std::string& port_name_pattern,
+		DataType type, PortFlags flags,
+		std::vector<std::string>& port_names) const
+{
+	int rv = 0;
+	regex_t port_regex;
+	bool use_regexp = false;
+	if (port_name_pattern.size () > 0) {
+		if (!regcomp (&port_regex, port_name_pattern.c_str (), REG_EXTENDED|REG_NOSUB)) {
+			use_regexp = true;
+		}
+	}
+	for (size_t i = 0; i < _ports.size (); ++i) {
+		PamPort* port = _ports[i];
+		if ((port->type () == type) && (port->flags () & flags)) {
+			if (!use_regexp || !regexec (&port_regex, port->name ().c_str (), 0, NULL, 0)) {
+				port_names.push_back (port->name ());
+				++rv;
+			}
+		}
+	}
+	if (use_regexp) {
+		regfree (&port_regex);
+	}
+	return rv;
+}
+
+DataType
+PortAudioBackend::port_data_type (PortEngine::PortHandle port) const
+{
+	if (!valid_port (port)) {
+		return DataType::NIL;
+	}
+	return static_cast<PamPort*>(port)->type ();
+}
+
+PortEngine::PortHandle
+PortAudioBackend::register_port (
+		const std::string& name,
+		ARDOUR::DataType type,
+		ARDOUR::PortFlags flags)
+{
+	if (name.size () == 0) { return 0; }
+	if (flags & IsPhysical) { return 0; }
+	return add_port (_instance_name + ":" + name, type, flags);
+}
+
+PortEngine::PortHandle
+PortAudioBackend::add_port (
+		const std::string& name,
+		ARDOUR::DataType type,
+		ARDOUR::PortFlags flags)
+{
+	assert(name.size ());
+	if (find_port (name)) {
+		PBD::error << _("PortAudioBackend::register_port: Port already exists:")
+				<< " (" << name << ")" << endmsg;
+		return 0;
+	}
+	PamPort* port = NULL;
+	switch (type) {
+		case DataType::AUDIO:
+			port = new PortAudioPort (*this, name, flags);
+			break;
+		case DataType::MIDI:
+			port = new PortMidiPort (*this, name, flags);
+			break;
+		default:
+			PBD::error << _("PortAudioBackend::register_port: Invalid Data Type.") << endmsg;
+			return 0;
+	}
+
+	_ports.push_back (port);
+
+	return port;
+}
+
+void
+PortAudioBackend::unregister_port (PortEngine::PortHandle port_handle)
+{
+	if (!_run) {
+		return;
+	}
+	PamPort* port = static_cast<PamPort*>(port_handle);
+	std::vector<PamPort*>::iterator i = std::find (_ports.begin (), _ports.end (), static_cast<PamPort*>(port_handle));
+	if (i == _ports.end ()) {
+		PBD::error << _("PortAudioBackend::unregister_port: Failed to find port") << endmsg;
+		return;
+	}
+	disconnect_all(port_handle);
+	_ports.erase (i);
+	delete port;
+}
+
+int
+PortAudioBackend::register_system_audio_ports()
+{
+	LatencyRange lr;
+
+	const uint32_t a_ins = _n_inputs;
+	const uint32_t a_out = _n_outputs;
+
+	// XXX PA reported stream latencies don't match measurements
+	const uint32_t portaudio_reported_input_latency =  _samples_per_period ; //  _pcmio->capture_latency();
+	const uint32_t portaudio_reported_output_latency = /* _samples_per_period + */ _pcmio->playback_latency();
+
+	/* audio ports */
+	lr.min = lr.max = portaudio_reported_input_latency + (_measure_latency ? 0 : _systemic_audio_input_latency);
+	for (uint32_t i = 0; i < a_ins; ++i) {
+		char tmp[64];
+		snprintf(tmp, sizeof(tmp), "system:capture_%d", i+1);
+		PortHandle p = add_port(std::string(tmp), DataType::AUDIO, static_cast<PortFlags>(IsOutput | IsPhysical | IsTerminal));
+		if (!p) return -1;
+		set_latency_range (p, false, lr);
+		_system_inputs.push_back(static_cast<PortAudioPort*>(p));
+	}
+
+	lr.min = lr.max = portaudio_reported_output_latency + (_measure_latency ? 0 : _systemic_audio_output_latency);
+	for (uint32_t i = 0; i < a_out; ++i) {
+		char tmp[64];
+		snprintf(tmp, sizeof(tmp), "system:playback_%d", i+1);
+		PortHandle p = add_port(std::string(tmp), DataType::AUDIO, static_cast<PortFlags>(IsInput | IsPhysical | IsTerminal));
+		if (!p) return -1;
+		set_latency_range (p, true, lr);
+		_system_outputs.push_back(static_cast<PamPort*>(p));
+	}
+	return 0;
+}
+
+void
+PortAudioBackend::unregister_ports (bool system_only)
+{
+	size_t i = 0;
+	_system_inputs.clear();
+	_system_outputs.clear();
+	_system_midi_in.clear();
+	_system_midi_out.clear();
+	while (i <  _ports.size ()) {
+		PamPort* port = _ports[i];
+		if (! system_only || (port->is_physical () && port->is_terminal ())) {
+			port->disconnect_all ();
+			delete port;
+			_ports.erase (_ports.begin() + i);
+		} else {
+			++i;
+		}
+	}
+}
+
+int
+PortAudioBackend::connect (const std::string& src, const std::string& dst)
+{
+	PamPort* src_port = find_port (src);
+	PamPort* dst_port = find_port (dst);
+
+	if (!src_port) {
+		PBD::error << _("PortAudioBackend::connect: Invalid Source port:")
+				<< " (" << src <<")" << endmsg;
+		return -1;
+	}
+	if (!dst_port) {
+		PBD::error << _("PortAudioBackend::connect: Invalid Destination port:")
+			<< " (" << dst <<")" << endmsg;
+		return -1;
+	}
+	return src_port->connect (dst_port);
+}
+
+int
+PortAudioBackend::disconnect (const std::string& src, const std::string& dst)
+{
+	PamPort* src_port = find_port (src);
+	PamPort* dst_port = find_port (dst);
+
+	if (!src_port || !dst_port) {
+		PBD::error << _("PortAudioBackend::disconnect: Invalid Port(s)") << endmsg;
+		return -1;
+	}
+	return src_port->disconnect (dst_port);
+}
+
+int
+PortAudioBackend::connect (PortEngine::PortHandle src, const std::string& dst)
+{
+	PamPort* dst_port = find_port (dst);
+	if (!valid_port (src)) {
+		PBD::error << _("PortAudioBackend::connect: Invalid Source Port Handle") << endmsg;
+		return -1;
+	}
+	if (!dst_port) {
+		PBD::error << _("PortAudioBackend::connect: Invalid Destination Port")
+			<< " (" << dst << ")" << endmsg;
+		return -1;
+	}
+	return static_cast<PamPort*>(src)->connect (dst_port);
+}
+
+int
+PortAudioBackend::disconnect (PortEngine::PortHandle src, const std::string& dst)
+{
+	PamPort* dst_port = find_port (dst);
+	if (!valid_port (src) || !dst_port) {
+		PBD::error << _("PortAudioBackend::disconnect: Invalid Port(s)") << endmsg;
+		return -1;
+	}
+	return static_cast<PamPort*>(src)->disconnect (dst_port);
+}
+
+int
+PortAudioBackend::disconnect_all (PortEngine::PortHandle port)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::disconnect_all: Invalid Port") << endmsg;
+		return -1;
+	}
+	static_cast<PamPort*>(port)->disconnect_all ();
+	return 0;
+}
+
+bool
+PortAudioBackend::connected (PortEngine::PortHandle port, bool /* process_callback_safe*/)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::disconnect_all: Invalid Port") << endmsg;
+		return false;
+	}
+	return static_cast<PamPort*>(port)->is_connected ();
+}
+
+bool
+PortAudioBackend::connected_to (PortEngine::PortHandle src, const std::string& dst, bool /*process_callback_safe*/)
+{
+	PamPort* dst_port = find_port (dst);
+	if (!valid_port (src) || !dst_port) {
+		PBD::error << _("PortAudioBackend::connected_to: Invalid Port") << endmsg;
+		return false;
+	}
+	return static_cast<PamPort*>(src)->is_connected (dst_port);
+}
+
+bool
+PortAudioBackend::physically_connected (PortEngine::PortHandle port, bool /*process_callback_safe*/)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::physically_connected: Invalid Port") << endmsg;
+		return false;
+	}
+	return static_cast<PamPort*>(port)->is_physically_connected ();
+}
+
+int
+PortAudioBackend::get_connections (PortEngine::PortHandle port, std::vector<std::string>& names, bool /*process_callback_safe*/)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PortAudioBackend::get_connections: Invalid Port") << endmsg;
+		return -1;
+	}
+
+	assert (0 == names.size ());
+
+	const std::vector<PamPort*>& connected_ports = static_cast<PamPort*>(port)->get_connections ();
+
+	for (std::vector<PamPort*>::const_iterator i = connected_ports.begin (); i != connected_ports.end (); ++i) {
+		names.push_back ((*i)->name ());
+	}
+
+	return (int)names.size ();
+}
+
+/* MIDI */
+int
+PortAudioBackend::midi_event_get (
+		pframes_t& timestamp,
+		size_t& size, uint8_t** buf, void* port_buffer,
+		uint32_t event_index)
+{
+	if (!buf || !port_buffer) return -1;
+	PortMidiBuffer& source = * static_cast<PortMidiBuffer*>(port_buffer);
+	if (event_index >= source.size ()) {
+		return -1;
+	}
+	PortMidiEvent * const event = source[event_index].get ();
+
+	timestamp = event->timestamp ();
+	size = event->size ();
+	*buf = event->data ();
+	return 0;
+}
+
+int
+PortAudioBackend::midi_event_put (
+		void* port_buffer,
+		pframes_t timestamp,
+		const uint8_t* buffer, size_t size)
+{
+	if (!buffer || !port_buffer) return -1;
+	PortMidiBuffer& dst = * static_cast<PortMidiBuffer*>(port_buffer);
+	if (dst.size () && (pframes_t)dst.back ()->timestamp () > timestamp) {
+#ifndef NDEBUG
+		// nevermind, ::get_buffer() sorts events
+		fprintf (stderr, "PortMidiBuffer: unordered event: %d > %d\n",
+				(pframes_t)dst.back ()->timestamp (), timestamp);
+#endif
+	}
+	dst.push_back (boost::shared_ptr<PortMidiEvent>(new PortMidiEvent (timestamp, buffer, size)));
+	return 0;
+}
+
+uint32_t
+PortAudioBackend::get_midi_event_count (void* port_buffer)
+{
+	if (!port_buffer) return 0;
+	return static_cast<PortMidiBuffer*>(port_buffer)->size ();
+}
+
+void
+PortAudioBackend::midi_clear (void* port_buffer)
+{
+	if (!port_buffer) return;
+	PortMidiBuffer * buf = static_cast<PortMidiBuffer*>(port_buffer);
+	assert (buf);
+	buf->clear ();
+}
+
+/* Monitoring */
+
+bool
+PortAudioBackend::can_monitor_input () const
+{
+	return false;
+}
+
+int
+PortAudioBackend::request_input_monitoring (PortEngine::PortHandle, bool)
+{
+	return -1;
+}
+
+int
+PortAudioBackend::ensure_input_monitoring (PortEngine::PortHandle, bool)
+{
+	return -1;
+}
+
+bool
+PortAudioBackend::monitoring_input (PortEngine::PortHandle)
+{
+	return false;
+}
+
+/* Latency management */
+
+void
+PortAudioBackend::set_latency_range (PortEngine::PortHandle port, bool for_playback, LatencyRange latency_range)
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PamPort::set_latency_range (): invalid port.") << endmsg;
+	}
+	static_cast<PamPort*>(port)->set_latency_range (latency_range, for_playback);
+}
+
+LatencyRange
+PortAudioBackend::get_latency_range (PortEngine::PortHandle port, bool for_playback)
+{
+	LatencyRange r;
+	if (!valid_port (port)) {
+		PBD::error << _("PamPort::get_latency_range (): invalid port.") << endmsg;
+		r.min = 0;
+		r.max = 0;
+		return r;
+	}
+	PamPort* p = static_cast<PamPort*>(port);
+	assert(p);
+
+	r = p->latency_range (for_playback);
+	// TODO MIDI
+	if (p->is_physical() && p->is_terminal() && p->type() == DataType::AUDIO) {
+		if (p->is_input() && for_playback) {
+			r.min += _samples_per_period;
+			r.max += _samples_per_period;
+		}
+		if (p->is_output() && !for_playback) {
+			r.min += _samples_per_period;
+			r.max += _samples_per_period;
+		}
+	}
+	return r;
+}
+
+/* Discovering physical ports */
+
+bool
+PortAudioBackend::port_is_physical (PortEngine::PortHandle port) const
+{
+	if (!valid_port (port)) {
+		PBD::error << _("PamPort::port_is_physical (): invalid port.") << endmsg;
+		return false;
+	}
+	return static_cast<PamPort*>(port)->is_physical ();
+}
+
+void
+PortAudioBackend::get_physical_outputs (DataType type, std::vector<std::string>& port_names)
+{
+	for (size_t i = 0; i < _ports.size (); ++i) {
+		PamPort* port = _ports[i];
+		if ((port->type () == type) && port->is_input () && port->is_physical ()) {
+			port_names.push_back (port->name ());
+		}
+	}
+}
+
+void
+PortAudioBackend::get_physical_inputs (DataType type, std::vector<std::string>& port_names)
+{
+	for (size_t i = 0; i < _ports.size (); ++i) {
+		PamPort* port = _ports[i];
+		if ((port->type () == type) && port->is_output () && port->is_physical ()) {
+			port_names.push_back (port->name ());
+		}
+	}
+}
+
+ChanCount
+PortAudioBackend::n_physical_outputs () const
+{
+	int n_midi = 0;
+	int n_audio = 0;
+	for (size_t i = 0; i < _ports.size (); ++i) {
+		PamPort* port = _ports[i];
+		if (port->is_output () && port->is_physical ()) {
+			switch (port->type ()) {
+				case DataType::AUDIO: ++n_audio; break;
+				case DataType::MIDI: ++n_midi; break;
+				default: break;
+			}
+		}
+	}
+	ChanCount cc;
+	cc.set (DataType::AUDIO, n_audio);
+	cc.set (DataType::MIDI, n_midi);
+	return cc;
+}
+
+ChanCount
+PortAudioBackend::n_physical_inputs () const
+{
+	int n_midi = 0;
+	int n_audio = 0;
+	for (size_t i = 0; i < _ports.size (); ++i) {
+		PamPort* port = _ports[i];
+		if (port->is_input () && port->is_physical ()) {
+			switch (port->type ()) {
+				case DataType::AUDIO: ++n_audio; break;
+				case DataType::MIDI: ++n_midi; break;
+				default: break;
+			}
+		}
+	}
+	ChanCount cc;
+	cc.set (DataType::AUDIO, n_audio);
+	cc.set (DataType::MIDI, n_midi);
+	return cc;
+}
+
+/* Getting access to the data buffer for a port */
+
+void*
+PortAudioBackend::get_buffer (PortEngine::PortHandle port, pframes_t nframes)
+{
+	if (!port || !valid_port (port)) return NULL;
+	return static_cast<PamPort*>(port)->get_buffer (nframes);
+}
+
+
+void *
+PortAudioBackend::main_process_thread ()
+{
+	AudioEngine::thread_init_callback (this);
+	_active = true;
+	_processed_samples = 0;
+
+	uint64_t clock1, clock2;
+	const int64_t nomial_time = 1e6 * _samples_per_period / _samplerate;
+
+	manager.registration_callback();
+	manager.graph_order_callback();
+
+	if (_pcmio->pcm_start()) {
+		_pcmio->pcm_stop ();
+		_active = false;
+		engine.halted_callback("PortAudio I/O error.");
+	}
+
+	while (_run) {
+
+		if (_freewheeling != _freewheel) {
+			_freewheel = _freewheeling;
+			engine.freewheel_callback (_freewheel);
+		}
+
+		if (!_freewheel) {
+
+			switch (_pcmio->next_cycle (_samples_per_period)) {
+				case 0: // OK
+					break;
+				case 1:
+#ifndef NDEBUG
+					printf("PortAudio: Xrun\n");
+#endif
+					engine.Xrun ();
+					break;
+				default:
+					PBD::error << _("PortAudioBackend: I/O error. Audio Process Terminated.") << endmsg;
+					break;
+			}
+
+			uint32_t i = 0;
+			clock1 = g_get_monotonic_time();
+
+			/* get audio */
+			i = 0;
+			for (std::vector<PamPort*>::const_iterator it = _system_inputs.begin (); it != _system_inputs.end (); ++it, ++i) {
+				_pcmio->get_capture_channel (i, (float*)((*it)->get_buffer(_samples_per_period)), _samples_per_period);
+			}
+
+			/* de-queue incoming midi*/
+			i=0;
+			for (std::vector<PamPort*>::const_iterator it = _system_midi_in.begin (); it != _system_midi_in.end (); ++it, ++i) {
+				PortMidiBuffer* mbuf = static_cast<PortMidiBuffer*>((*it)->get_buffer(0));
+				mbuf->clear();
+			}
+
+			/* clear output buffers */
+			for (std::vector<PamPort*>::const_iterator it = _system_outputs.begin (); it != _system_outputs.end (); ++it) {
+				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)) {
+				_pcmio->pcm_stop ();
+				_active = false;
+				return 0;
+			}
+#if 0
+			/* mixdown midi */
+			for (std::vector<PamPort*>::iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it) {
+				static_cast<PortBackendMidiPort*>(*it)->next_period();
+			}
+
+			/* queue outgoing midi */
+			i = 0;
+			for (std::vector<PamPort*>::const_iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it, ++i) {
+				// TODO
+			}
+#endif
+
+			/* write back audio */
+			i = 0;
+			for (std::vector<PamPort*>::const_iterator it = _system_outputs.begin (); it != _system_outputs.end (); ++it, ++i) {
+				_pcmio->set_playback_channel (i, (float const*)(*it)->get_buffer (_samples_per_period), _samples_per_period);
+			}
+
+			_processed_samples += _samples_per_period;
+
+			/* calculate DSP load */
+			clock2 = g_get_monotonic_time();
+			const int64_t elapsed_time = clock2 - clock1;
+			_dsp_load = elapsed_time / (float) nomial_time;
+
+		} else {
+			// Freewheelin'
+
+			// zero audio input buffers
+			for (std::vector<PamPort*>::const_iterator it = _system_inputs.begin (); it != _system_inputs.end (); ++it) {
+				memset ((*it)->get_buffer (_samples_per_period), 0, _samples_per_period * sizeof (Sample));
+			}
+
+			clock1 = g_get_monotonic_time();
+
+			// TODO clear midi or stop midi recv when entering fwheelin'
+
+			_last_process_start = 0;
+			if (engine.process_callback (_samples_per_period)) {
+				_pcmio->pcm_stop ();
+				_active = false;
+				return 0;
+			}
+
+			// drop all outgoing MIDI messages
+			for (std::vector<PamPort*>::const_iterator it = _system_midi_out.begin (); it != _system_midi_out.end (); ++it) {
+					void *bptr = (*it)->get_buffer(0);
+					midi_clear(bptr);
+			}
+
+			_dsp_load = 1.0;
+			Glib::usleep (100); // don't hog cpu
+		}
+
+		bool connections_changed = false;
+		bool ports_changed = false;
+		if (!pthread_mutex_trylock (&_port_callback_mutex)) {
+			if (_port_change_flag) {
+				ports_changed = true;
+				_port_change_flag = false;
+			}
+			if (!_port_connection_queue.empty ()) {
+				connections_changed = true;
+			}
+			while (!_port_connection_queue.empty ()) {
+				PortConnectData *c = _port_connection_queue.back ();
+				manager.connect_callback (c->a, c->b, c->c);
+				_port_connection_queue.pop_back ();
+				delete c;
+			}
+			pthread_mutex_unlock (&_port_callback_mutex);
+		}
+		if (ports_changed) {
+			manager.registration_callback();
+		}
+		if (connections_changed) {
+			manager.graph_order_callback();
+		}
+		if (connections_changed || ports_changed) {
+			engine.latency_callback(false);
+			engine.latency_callback(true);
+		}
+
+	}
+	_pcmio->pcm_stop ();
+	_active = false;
+	if (_run) {
+		engine.halted_callback("PortAudio I/O error.");
+	}
+	return 0;
+}
+
+
+/******************************************************************************/
+
+static boost::shared_ptr<PortAudioBackend> _instance;
+
+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 = {
+	"PortAudio",
+	instantiate,
+	deinstantiate,
+	backend_factory,
+	already_configured,
+	available
+};
+
+static boost::shared_ptr<AudioBackend>
+backend_factory (AudioEngine& e)
+{
+	if (!_instance) {
+		_instance.reset (new PortAudioBackend (e, _descriptor));
+	}
+	return _instance;
+}
+
+static int
+instantiate (const std::string& arg1, const std::string& /* arg2 */)
+{
+	s_instance_name = arg1;
+	return 0;
+}
+
+static int
+deinstantiate ()
+{
+	_instance.reset ();
+	return 0;
+}
+
+static bool
+already_configured ()
+{
+	return false;
+}
+
+static bool
+available ()
+{
+	return true;
+}
+
+extern "C" ARDOURBACKEND_API ARDOUR::AudioBackendInfo* descriptor ()
+{
+	return &_descriptor;
+}
+
+
+/******************************************************************************/
+PamPort::PamPort (PortAudioBackend &b, const std::string& name, PortFlags flags)
+	: _osx_backend (b)
+	, _name  (name)
+	, _flags (flags)
+{
+	_capture_latency_range.min = 0;
+	_capture_latency_range.max = 0;
+	_playback_latency_range.min = 0;
+	_playback_latency_range.max = 0;
+}
+
+PamPort::~PamPort () {
+	disconnect_all ();
+}
+
+
+int PamPort::connect (PamPort *port)
+{
+	if (!port) {
+		PBD::error << _("PamPort::connect (): invalid (null) port") << endmsg;
+		return -1;
+	}
+
+	if (type () != port->type ()) {
+		PBD::error << _("PamPort::connect (): wrong port-type") << endmsg;
+		return -1;
+	}
+
+	if (is_output () && port->is_output ()) {
+		PBD::error << _("PamPort::connect (): cannot inter-connect output ports.") << endmsg;
+		return -1;
+	}
+
+	if (is_input () && port->is_input ()) {
+		PBD::error << _("PamPort::connect (): cannot inter-connect input ports.") << endmsg;
+		return -1;
+	}
+
+	if (this == port) {
+		PBD::error << _("PamPort::connect (): cannot self-connect ports.") << endmsg;
+		return -1;
+	}
+
+	if (is_connected (port)) {
+#if 0 // don't bother to warn about this for now. just ignore it
+		PBD::error << _("PamPort::connect (): ports are already connected:")
+			<< " (" << name () << ") -> (" << port->name () << ")"
+			<< endmsg;
+#endif
+		return -1;
+	}
+
+	_connect (port, true);
+	return 0;
+}
+
+
+void PamPort::_connect (PamPort *port, bool callback)
+{
+	_connections.push_back (port);
+	if (callback) {
+		port->_connect (this, false);
+		_osx_backend.port_connect_callback (name(),  port->name(), true);
+	}
+}
+
+int PamPort::disconnect (PamPort *port)
+{
+	if (!port) {
+		PBD::error << _("PamPort::disconnect (): invalid (null) port") << endmsg;
+		return -1;
+	}
+
+	if (!is_connected (port)) {
+		PBD::error << _("PamPort::disconnect (): ports are not connected:")
+			<< " (" << name () << ") -> (" << port->name () << ")"
+			<< endmsg;
+		return -1;
+	}
+	_disconnect (port, true);
+	return 0;
+}
+
+void PamPort::_disconnect (PamPort *port, bool callback)
+{
+	std::vector<PamPort*>::iterator it = std::find (_connections.begin (), _connections.end (), port);
+
+	assert (it != _connections.end ());
+
+	_connections.erase (it);
+
+	if (callback) {
+		port->_disconnect (this, false);
+		_osx_backend.port_connect_callback (name(),  port->name(), false);
+	}
+}
+
+
+void PamPort::disconnect_all ()
+{
+	while (!_connections.empty ()) {
+		_connections.back ()->_disconnect (this, false);
+		_osx_backend.port_connect_callback (name(),  _connections.back ()->name(), false);
+		_connections.pop_back ();
+	}
+}
+
+bool
+PamPort::is_connected (const PamPort *port) const
+{
+	return std::find (_connections.begin (), _connections.end (), port) != _connections.end ();
+}
+
+bool PamPort::is_physically_connected () const
+{
+	for (std::vector<PamPort*>::const_iterator it = _connections.begin (); it != _connections.end (); ++it) {
+		if ((*it)->is_physical ()) {
+			return true;
+		}
+	}
+	return false;
+}
+
+/******************************************************************************/
+
+PortAudioPort::PortAudioPort (PortAudioBackend &b, const std::string& name, PortFlags flags)
+	: PamPort (b, name, flags)
+{
+	memset (_buffer, 0, sizeof (_buffer));
+#ifndef PLATFORM_WINDOWS
+	mlock(_buffer, sizeof (_buffer));
+#endif
+}
+
+PortAudioPort::~PortAudioPort () { }
+
+void* PortAudioPort::get_buffer (pframes_t n_samples)
+{
+	if (is_input ()) {
+		std::vector<PamPort*>::const_iterator it = get_connections ().begin ();
+		if (it == get_connections ().end ()) {
+			memset (_buffer, 0, n_samples * sizeof (Sample));
+		} else {
+			PortAudioPort const * source = static_cast<const PortAudioPort*>(*it);
+			assert (source && source->is_output ());
+			memcpy (_buffer, source->const_buffer (), n_samples * sizeof (Sample));
+			while (++it != get_connections ().end ()) {
+				source = static_cast<const PortAudioPort*>(*it);
+				assert (source && source->is_output ());
+				Sample* dst = buffer ();
+				const Sample* src = source->const_buffer ();
+				for (uint32_t s = 0; s < n_samples; ++s, ++dst, ++src) {
+					*dst += *src;
+				}
+			}
+		}
+	}
+	return _buffer;
+}
+
+
+PortMidiPort::PortMidiPort (PortAudioBackend &b, const std::string& name, PortFlags flags)
+	: PamPort (b, name, flags)
+	, _n_periods (1)
+	, _bufperiod (0)
+{
+	_buffer[0].clear ();
+	_buffer[1].clear ();
+}
+
+PortMidiPort::~PortMidiPort () { }
+
+struct MidiEventSorter {
+	bool operator() (const boost::shared_ptr<PortMidiEvent>& a, const boost::shared_ptr<PortMidiEvent>& b) {
+		return *a < *b;
+	}
+};
+
+void* PortMidiPort::get_buffer (pframes_t /* nframes */)
+{
+	if (is_input ()) {
+		(_buffer[_bufperiod]).clear ();
+		for (std::vector<PamPort*>::const_iterator i = get_connections ().begin ();
+				i != get_connections ().end ();
+				++i) {
+			const PortMidiBuffer * src = static_cast<const PortMidiPort*>(*i)->const_buffer ();
+			for (PortMidiBuffer::const_iterator it = src->begin (); it != src->end (); ++it) {
+				(_buffer[_bufperiod]).push_back (boost::shared_ptr<PortMidiEvent>(new PortMidiEvent (**it)));
+			}
+		}
+		std::sort ((_buffer[_bufperiod]).begin (), (_buffer[_bufperiod]).end (), MidiEventSorter());
+	}
+	return &(_buffer[_bufperiod]);
+}
+
+PortMidiEvent::PortMidiEvent (const pframes_t timestamp, const uint8_t* data, size_t size)
+	: _size (size)
+	, _timestamp (timestamp)
+	, _data (0)
+{
+	if (size > 0) {
+		_data = (uint8_t*) malloc (size);
+		memcpy (_data, data, size);
+	}
+}
+
+PortMidiEvent::PortMidiEvent (const PortMidiEvent& other)
+	: _size (other.size ())
+	, _timestamp (other.timestamp ())
+	, _data (0)
+{
+	if (other.size () && other.const_data ()) {
+		_data = (uint8_t*) malloc (other.size ());
+		memcpy (_data, other.const_data (), other.size ());
+	}
+};
+
+PortMidiEvent::~PortMidiEvent () {
+	free (_data);
+};
diff --git a/libs/backends/portaudio/portaudio_backend.h b/libs/backends/portaudio/portaudio_backend.h
new file mode 100644
index 0000000000..36aebe0f14
--- /dev/null
+++ b/libs/backends/portaudio/portaudio_backend.h
@@ -0,0 +1,413 @@
+/*
+ * Copyright (C) 2014-2015 Robin Gareus <robin@gareus.org>
+ * Copyright (C) 2013 Paul Davis
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef __libbackend_portaudio_backend_h__
+#define __libbackend_portaudio_backend_h__
+
+#include <string>
+#include <vector>
+#include <set>
+
+#include <stdint.h>
+#include <pthread.h>
+
+#include <boost/shared_ptr.hpp>
+
+#include "ardour/audio_backend.h"
+#include "ardour/types.h"
+
+#include "portaudio_io.h"
+
+namespace ARDOUR {
+
+class PortAudioBackend;
+
+class PortMidiEvent {
+	public:
+		PortMidiEvent (const pframes_t timestamp, const uint8_t* data, size_t size);
+		PortMidiEvent (const PortMidiEvent& other);
+		~PortMidiEvent ();
+		size_t size () const { return _size; };
+		pframes_t timestamp () const { return _timestamp; };
+		const unsigned char* const_data () const { return _data; };
+		unsigned char* data () { return _data; };
+		bool operator< (const PortMidiEvent &other) const { return timestamp () < other.timestamp (); };
+	private:
+		size_t _size;
+		pframes_t _timestamp;
+		uint8_t *_data;
+};
+
+typedef std::vector<boost::shared_ptr<PortMidiEvent> > PortMidiBuffer;
+
+class PamPort { // PortAudio / PortMidi Backend Port
+	protected:
+		PamPort (PortAudioBackend &b, const std::string&, PortFlags);
+	public:
+		virtual ~PamPort ();
+
+		const std::string& name () const { return _name; }
+		PortFlags flags () const { return _flags; }
+
+		int set_name (const std::string &name) { _name = name; return 0; }
+
+		virtual DataType type () const = 0;
+
+		bool is_input ()     const { return flags () & IsInput; }
+		bool is_output ()    const { return flags () & IsOutput; }
+		bool is_physical ()  const { return flags () & IsPhysical; }
+		bool is_terminal ()  const { return flags () & IsTerminal; }
+		bool is_connected () const { return _connections.size () != 0; }
+		bool is_connected (const PamPort *port) const;
+		bool is_physically_connected () const;
+
+		const std::vector<PamPort *>& get_connections () const { return _connections; }
+
+		int connect (PamPort *port);
+		int disconnect (PamPort *port);
+		void disconnect_all ();
+
+		virtual void* get_buffer (pframes_t nframes) = 0;
+
+		const LatencyRange latency_range (bool for_playback) const
+		{
+			return for_playback ? _playback_latency_range : _capture_latency_range;
+		}
+
+		void set_latency_range (const LatencyRange &latency_range, bool for_playback)
+		{
+			if (for_playback)
+			{
+				_playback_latency_range = latency_range;
+			}
+			else
+			{
+				_capture_latency_range = latency_range;
+			}
+		}
+
+	private:
+		PortAudioBackend &_osx_backend;
+		std::string _name;
+		const PortFlags _flags;
+		LatencyRange _capture_latency_range;
+		LatencyRange _playback_latency_range;
+		std::vector<PamPort*> _connections;
+
+		void _connect (PamPort* , bool);
+		void _disconnect (PamPort* , bool);
+
+}; // class PamPort
+
+class PortAudioPort : public PamPort {
+	public:
+		PortAudioPort (PortAudioBackend &b, const std::string&, PortFlags);
+		~PortAudioPort ();
+
+		DataType type () const { return DataType::AUDIO; };
+
+		Sample* buffer () { return _buffer; }
+		const Sample* const_buffer () const { return _buffer; }
+		void* get_buffer (pframes_t nframes);
+
+	private:
+		Sample _buffer[8192];
+}; // class PortAudioPort
+
+class PortMidiPort : public PamPort {
+	public:
+		PortMidiPort (PortAudioBackend &b, const std::string&, PortFlags);
+		~PortMidiPort ();
+
+		DataType type () const { return DataType::MIDI; };
+
+		void* get_buffer (pframes_t nframes);
+		const PortMidiBuffer * 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; } }
+
+	private:
+		PortMidiBuffer _buffer[2];
+		int _n_periods;
+		int _bufperiod;
+}; // class PortMidiPort
+
+class PortAudioBackend : public AudioBackend {
+	friend class PamPort;
+	public:
+		PortAudioBackend (AudioEngine& e, AudioBackendInfo& info);
+		~PortAudioBackend ();
+
+		/* AUDIOBACKEND API */
+
+		std::string name () const;
+		bool is_realtime () const;
+
+		std::vector<DeviceStatus> enumerate_devices () const;
+		std::vector<float> available_sample_rates (const std::string& device) const;
+		std::vector<uint32_t> available_buffer_sizes (const std::string& device) const;
+		uint32_t available_input_channel_count (const std::string& device) const;
+		uint32_t available_output_channel_count (const std::string& device) const;
+
+		bool can_change_sample_rate_when_running () const;
+		bool can_change_buffer_size_when_running () const;
+
+		int set_device_name (const std::string&);
+		int set_sample_rate (float);
+		int set_buffer_size (uint32_t);
+		int set_interleaved (bool yn);
+		int set_input_channels (uint32_t);
+		int set_output_channels (uint32_t);
+		int set_systemic_input_latency (uint32_t);
+		int set_systemic_output_latency (uint32_t);
+		int set_systemic_midi_input_latency (std::string const, uint32_t) { return 0; }
+		int set_systemic_midi_output_latency (std::string const, uint32_t) { return 0; }
+
+		int reset_device () { return 0; };
+
+		/* Retrieving parameters */
+		std::string  device_name () const;
+		float        sample_rate () const;
+		uint32_t     buffer_size () const;
+		bool         interleaved () const;
+		uint32_t     input_channels () const;
+		uint32_t     output_channels () const;
+		uint32_t     systemic_input_latency () const;
+		uint32_t     systemic_output_latency () const;
+		uint32_t     systemic_midi_input_latency (std::string const) const { return 0; }
+		uint32_t     systemic_midi_output_latency (std::string const) const { return 0; }
+
+		bool can_set_systemic_midi_latencies () const { return false; }
+
+		/* External control app */
+		std::string control_app_name () const { return std::string (); }
+		void launch_control_app () {}
+
+		/* MIDI */
+		std::vector<std::string> enumerate_midi_options () const;
+		int set_midi_option (const std::string&);
+		std::string midi_option () const;
+
+		std::vector<DeviceStatus> enumerate_midi_devices () const {
+			return std::vector<AudioBackend::DeviceStatus> ();
+		}
+		int set_midi_device_enabled (std::string const, bool) {
+			return 0;
+		}
+		bool midi_device_enabled (std::string const) const {
+			return true;
+		}
+
+	protected:
+		/* State Control */
+		int _start (bool for_latency_measurement);
+	public:
+		int stop ();
+		int freewheel (bool);
+		float dsp_load () const;
+		size_t raw_buffer_size (DataType t);
+
+		/* Process time */
+		framepos_t sample_time ();
+		framepos_t sample_time_at_cycle_start ();
+		pframes_t samples_since_cycle_start ();
+
+		int create_process_thread (boost::function<void()> func);
+		int join_process_threads ();
+		bool in_process_thread ();
+		uint32_t process_thread_count ();
+
+		void update_latencies ();
+
+		/* PORTENGINE API */
+
+		void* private_handle () const;
+		const std::string& my_name () const;
+		bool available () const;
+		uint32_t port_name_size () const;
+
+		int         set_port_name (PortHandle, const std::string&);
+		std::string get_port_name (PortHandle) const;
+		PortHandle  get_port_by_name (const std::string&) const;
+
+		int get_ports (const std::string& port_name_pattern, DataType type, PortFlags flags, std::vector<std::string>&) const;
+
+		DataType port_data_type (PortHandle) const;
+
+		PortHandle register_port (const std::string& shortname, ARDOUR::DataType, ARDOUR::PortFlags);
+		void unregister_port (PortHandle);
+
+		int  connect (const std::string& src, const std::string& dst);
+		int  disconnect (const std::string& src, const std::string& dst);
+		int  connect (PortHandle, const std::string&);
+		int  disconnect (PortHandle, const std::string&);
+		int  disconnect_all (PortHandle);
+
+		bool connected (PortHandle, bool process_callback_safe);
+		bool connected_to (PortHandle, const std::string&, bool process_callback_safe);
+		bool physically_connected (PortHandle, bool process_callback_safe);
+		int  get_connections (PortHandle, std::vector<std::string>&, bool process_callback_safe);
+
+		/* MIDI */
+		int midi_event_get (pframes_t& timestamp, size_t& size, uint8_t** buf, void* port_buffer, uint32_t event_index);
+		int midi_event_put (void* port_buffer, pframes_t timestamp, const uint8_t* buffer, size_t size);
+		uint32_t get_midi_event_count (void* port_buffer);
+		void     midi_clear (void* port_buffer);
+
+		/* Monitoring */
+
+		bool can_monitor_input () const;
+		int  request_input_monitoring (PortHandle, bool);
+		int  ensure_input_monitoring (PortHandle, bool);
+		bool monitoring_input (PortHandle);
+
+		/* Latency management */
+
+		void         set_latency_range (PortHandle, bool for_playback, LatencyRange);
+		LatencyRange get_latency_range (PortHandle, bool for_playback);
+
+		/* Discovering physical ports */
+
+		bool      port_is_physical (PortHandle) const;
+		void      get_physical_outputs (DataType type, std::vector<std::string>&);
+		void      get_physical_inputs (DataType type, std::vector<std::string>&);
+		ChanCount n_physical_outputs () const;
+		ChanCount n_physical_inputs () const;
+
+		/* Getting access to the data buffer for a port */
+
+		void* get_buffer (PortHandle, pframes_t);
+
+		void* main_process_thread ();
+
+	private:
+		std::string _instance_name;
+		PortAudioIO *_pcmio;
+
+		bool  _run; /* keep going or stop, ardour thread */
+		bool  _active; /* is running, process thread */
+		bool  _freewheel;
+		bool  _freewheeling;
+		bool  _measure_latency;
+
+		uint64_t _last_process_start;
+
+		static std::vector<std::string> _midi_options;
+		static std::vector<AudioBackend::DeviceStatus> _audio_device_status;
+		static std::vector<AudioBackend::DeviceStatus> _midi_device_status;
+
+		mutable std::string _audio_device;
+		std::string _midi_driver_option;
+
+		/* audio settings */
+		float  _samplerate;
+		size_t _samples_per_period;
+		static size_t _max_buffer_size;
+
+		uint32_t _n_inputs;
+		uint32_t _n_outputs;
+
+		uint32_t _systemic_audio_input_latency;
+		uint32_t _systemic_audio_output_latency;
+
+		/* portaudio specific  */
+		int name_to_id(std::string) const;
+
+		/* processing */
+		float  _dsp_load;
+		framecnt_t _processed_samples;
+		pthread_t _main_thread;
+
+		/* process threads */
+		static void* portaudio_process_thread (void *);
+		std::vector<pthread_t> _threads;
+
+		struct ThreadData {
+			PortAudioBackend* engine;
+			boost::function<void ()> f;
+			size_t stacksize;
+
+			ThreadData (PortAudioBackend* e, boost::function<void ()> fp, size_t stacksz)
+				: engine (e) , f (fp) , stacksize (stacksz) {}
+		};
+
+		/* port engine */
+		PortHandle add_port (const std::string& shortname, ARDOUR::DataType, ARDOUR::PortFlags);
+		int register_system_audio_ports ();
+		void unregister_ports (bool system_only = false);
+
+		std::vector<PamPort *> _ports;
+		std::vector<PamPort *> _system_inputs;
+		std::vector<PamPort *> _system_outputs;
+		std::vector<PamPort *> _system_midi_in;
+		std::vector<PamPort *> _system_midi_out;
+
+		struct PortConnectData {
+			std::string a;
+			std::string b;
+			bool c;
+
+			PortConnectData (const std::string& a, const std::string& b, bool c)
+				: a (a) , b (b) , c (c) {}
+		};
+
+		std::vector<PortConnectData *> _port_connection_queue;
+		pthread_mutex_t _port_callback_mutex;
+		bool _port_change_flag;
+
+		void port_connect_callback (const std::string& a, const std::string& b, bool conn) {
+			pthread_mutex_lock (&_port_callback_mutex);
+			_port_connection_queue.push_back(new PortConnectData(a, b, conn));
+			pthread_mutex_unlock (&_port_callback_mutex);
+		}
+
+		void port_connect_add_remove_callback () {
+			pthread_mutex_lock (&_port_callback_mutex);
+			_port_change_flag = true;
+			pthread_mutex_unlock (&_port_callback_mutex);
+		}
+
+		bool valid_port (PortHandle port) const {
+			return std::find (_ports.begin (), _ports.end (), (PamPort*)port) != _ports.end ();
+		}
+
+		PamPort * find_port (const std::string& port_name) const {
+			for (std::vector<PamPort*>::const_iterator it = _ports.begin (); it != _ports.end (); ++it) {
+				if ((*it)->name () == port_name) {
+					return *it;
+				}
+			}
+			return NULL;
+		}
+
+		PamPort * find_port_in (std::vector<PamPort *> plist, const std::string& port_name) const {
+			for (std::vector<PamPort*>::const_iterator it = plist.begin (); it != plist.end (); ++it) {
+				if ((*it)->name () == port_name) {
+					return *it;
+				}
+			}
+			return NULL;
+		}
+
+}; // class PortAudioBackend
+
+} // namespace
+
+#endif /* __libbackend_portaudio_backend_h__ */
diff --git a/libs/backends/portaudio/portaudio_io.cc b/libs/backends/portaudio/portaudio_io.cc
new file mode 100644
index 0000000000..e4e2fabbb7
--- /dev/null
+++ b/libs/backends/portaudio/portaudio_io.cc
@@ -0,0 +1,452 @@
+/*
+ * Copyright (C) 2015 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <assert.h>
+#include "portaudio_io.h"
+
+using namespace ARDOUR;
+
+PortAudioIO::PortAudioIO ()
+	: _state (-1)
+	, _initialized (false)
+	, _capture_channels (0)
+	, _playback_channels (0)
+	, _stream (0)
+	, _input_buffer (0)
+	, _output_buffer (0)
+	, _cur_sample_rate (0)
+	, _cur_input_latency (0)
+	, _cur_output_latency (0)
+{
+}
+
+PortAudioIO::~PortAudioIO ()
+{
+	if (_state == 0) {
+		pcm_stop();
+	}
+	if (_initialized) {
+		Pa_Terminate();
+	}
+
+	for (std::map<int, paDevice*>::const_iterator i = _devices.begin (); i != _devices.end(); ++i) {
+		delete i->second;
+	}
+	_devices.clear();
+
+	free (_input_buffer); _input_buffer = NULL;
+	free (_output_buffer); _output_buffer = NULL;
+}
+
+
+int
+PortAudioIO::available_sample_rates(int device_id, std::vector<float>& sampleRates)
+{
+	static const float ardourRates[] = { 8000.0, 22050.0, 24000.0, 44100.0, 48000.0, 88200.0, 96000.0, 176400.0, 192000.0};
+
+	assert(_initialized);
+
+	// TODO use  separate int device_input, int device_output ?!
+	if (device_id == -1) {
+		device_id = Pa_GetDefaultInputDevice();
+	}
+#ifndef NDEBUG
+	printf("PortAudio: Querying Samplerates for device %d\n", device_id);
+#endif
+
+	sampleRates.clear();
+	const PaDeviceInfo* nfo = Pa_GetDeviceInfo(device_id);
+
+        PaStreamParameters inputParam;
+        PaStreamParameters outputParam;
+
+        inputParam.device = device_id;
+        inputParam.channelCount = nfo->maxInputChannels;
+        inputParam.sampleFormat = paFloat32;
+        inputParam.suggestedLatency = 0;
+        inputParam.hostApiSpecificStreamInfo = 0;
+
+        outputParam.device = device_id;
+        outputParam.channelCount = nfo->maxOutputChannels;
+        outputParam.sampleFormat = paFloat32;
+        outputParam.suggestedLatency = 0;
+        outputParam.hostApiSpecificStreamInfo = 0;
+
+	for (uint32_t i = 0; i < sizeof(ardourRates)/sizeof(float); ++i) {
+		if (paFormatIsSupported == Pa_IsFormatSupported(
+					nfo->maxInputChannels > 0 ? &inputParam : NULL,
+					nfo->maxOutputChannels > 0 ? &outputParam : NULL,
+					ardourRates[i])) {
+			sampleRates.push_back (ardourRates[i]);
+		}
+	}
+
+	if (sampleRates.empty()) {
+		sampleRates.push_back (48000.0);
+	}
+
+	return 0;
+}
+
+int
+PortAudioIO::available_buffer_sizes(int device_id, std::vector<uint32_t>& bufferSizes)
+{
+	// TODO
+	static const uint32_t ardourSizes[] = { 64, 128, 256, 512, 1024, 2048, 4096 };
+	for(uint32_t i = 0; i < sizeof(ardourSizes)/sizeof(uint32_t); ++i) {
+		bufferSizes.push_back (ardourSizes[i]);
+	}
+	return 0;
+}
+
+void
+PortAudioIO::device_list (std::map<int, std::string> &devices) const {
+	devices.clear();
+	for (std::map<int, paDevice*>::const_iterator i = _devices.begin (); i != _devices.end(); ++i) {
+		devices.insert (std::pair<int, std::string> (i->first, i->second->name));
+	}
+}
+
+void
+PortAudioIO::discover()
+{
+	for (std::map<int, paDevice*>::const_iterator i = _devices.begin (); i != _devices.end(); ++i) {
+		delete i->second;
+	}
+	_devices.clear();
+	
+	PaError err = paNoError;
+
+	if (!_initialized) {
+		err = Pa_Initialize();
+	}
+	if (err != paNoError) {
+		return;
+	}
+
+	_initialized = true;
+
+	{
+		const PaDeviceInfo* nfo_i = Pa_GetDeviceInfo(Pa_GetDefaultInputDevice());
+		const PaDeviceInfo* nfo_o = Pa_GetDeviceInfo(Pa_GetDefaultOutputDevice());
+		if (nfo_i && nfo_o) {
+			_devices.insert (std::pair<int, paDevice*> (-1,
+						new paDevice("Default",
+							nfo_i->maxInputChannels,
+							nfo_o->maxOutputChannels
+							)));
+		}
+	}
+
+	int n_devices = Pa_GetDeviceCount();
+#ifndef NDEBUG
+	printf("PortAudio %d devices found:\n", n_devices);
+#endif
+
+	for (int i = 0 ; i < n_devices; ++i) {
+		const PaDeviceInfo* nfo = Pa_GetDeviceInfo(i);
+		if (!nfo) continue;
+#ifndef NDEBUG
+		printf(" (%d) '%s' in: %d (lat: %.1f .. %.1f) out: %d (lat: %.1f .. %.1f) sr:%.2f\n",
+				i, nfo->name,
+				nfo->maxInputChannels,
+				nfo->defaultLowInputLatency * 1e3,
+				nfo->defaultHighInputLatency * 1e3,
+				nfo->maxOutputChannels,
+				nfo->defaultLowOutputLatency * 1e3,
+				nfo->defaultHighOutputLatency * 1e3,
+				nfo->defaultSampleRate);
+#endif
+		if ( nfo->maxInputChannels == 0 && nfo->maxOutputChannels == 0) {
+			continue;
+		}
+		_devices.insert (std::pair<int, paDevice*> (i, new paDevice(
+						nfo->name,
+						nfo->maxInputChannels,
+						nfo->maxOutputChannels
+						)));
+	}
+}
+
+void
+PortAudioIO::pcm_stop ()
+{
+	if (_stream) {
+		Pa_CloseStream (_stream);
+	}
+	_stream = NULL;
+
+	_capture_channels = 0;
+	_playback_channels = 0;
+	_cur_sample_rate = 0;
+	_cur_input_latency = 0;
+	_cur_output_latency = 0;
+
+	free (_input_buffer); _input_buffer = NULL;
+	free (_output_buffer); _output_buffer = NULL;
+	_state = -1;
+}
+
+int
+PortAudioIO::pcm_start()
+{
+	PaError err = Pa_StartStream (_stream);
+
+	if (err != paNoError) {
+		_state = -1;
+		return -1;
+	}
+	return 0;
+}
+
+#ifdef __APPLE__
+static uint32_t lower_power_of_two (uint32_t v) {
+	v--;
+	v |= v >> 1;
+	v |= v >> 2;
+	v |= v >> 4;
+	v |= v >> 8;
+	v |= v >> 16;
+	v++;
+	return v >> 1;
+}
+#endif
+
+int
+PortAudioIO::pcm_setup (
+		int device_input, int device_output,
+		double sample_rate, uint32_t samples_per_period)
+{
+	_state = -2;
+
+	// TODO error reporting sans fprintf()
+
+	PaError err = paNoError;
+	const PaDeviceInfo *nfo_in;
+	const PaDeviceInfo *nfo_out;
+	const PaStreamInfo *nfo_s;
+		
+	if (!_initialized) {
+		err = Pa_Initialize();
+	}
+	if (err != paNoError) {
+		fprintf(stderr, "PortAudio Initialization Failed\n");
+		goto error;
+	}
+	_initialized = true;
+
+
+	if (device_input == -1) {
+		device_input = Pa_GetDefaultInputDevice();
+	}
+	if (device_output == -1) {
+		device_output = Pa_GetDefaultOutputDevice();
+	}
+
+	_capture_channels = 0;
+	_playback_channels = 0;
+	_cur_sample_rate = 0;
+	_cur_input_latency = 0;
+	_cur_output_latency = 0;
+
+#ifndef NDEBUG
+	printf("PortAudio Device IDs: i:%d o:%d\n", device_input, device_output);
+#endif
+
+	nfo_in = Pa_GetDeviceInfo(device_input);
+	nfo_out = Pa_GetDeviceInfo(device_output);
+
+	if (!nfo_in && ! nfo_out) {
+		fprintf(stderr, "PortAudio Cannot Query Device Info\n");
+		goto error;
+	}
+
+	if (nfo_in) {
+		_capture_channels = nfo_in->maxInputChannels;
+	}
+	if (nfo_out) {
+		_playback_channels = nfo_out->maxOutputChannels;
+	}
+
+	if(_capture_channels == 0 && _playback_channels == 0) {
+		fprintf(stderr, "PortAudio no Input and no output channels.\n");
+		goto error;
+	}
+
+
+#ifdef __APPLE__
+	// pa_mac_core_blocking.c pa_stable_v19_20140130
+	// BUG: ringbuffer alloc requires power-of-two chn count.
+	if ((_capture_channels & (_capture_channels - 1)) != 0) {
+		printf("Adjusted capture channes to power of two (portaudio rb bug)\n");
+		_capture_channels = lower_power_of_two (_capture_channels);
+	}
+
+	if ((_playback_channels & (_playback_channels - 1)) != 0) {
+		printf("Adjusted capture channes to power of two (portaudio rb bug)\n");
+		_playback_channels = lower_power_of_two (_playback_channels);
+	}
+#endif
+	
+#ifndef NDEBUG
+	printf("PortAudio Channels: in:%d out:%d\n",
+			_capture_channels, _playback_channels);
+#endif
+
+	PaStreamParameters inputParam;
+	PaStreamParameters outputParam;
+
+	if (nfo_in) {
+		inputParam.device = device_input;
+		inputParam.channelCount = _capture_channels;
+		inputParam.sampleFormat = paFloat32;
+		inputParam.suggestedLatency = nfo_in->defaultLowInputLatency;
+		inputParam.hostApiSpecificStreamInfo = NULL;
+	}
+
+	if (nfo_out) {
+		outputParam.device = device_output;
+		outputParam.channelCount = _playback_channels;
+		outputParam.sampleFormat = paFloat32;
+		outputParam.suggestedLatency = nfo_out->defaultLowOutputLatency;
+		outputParam.hostApiSpecificStreamInfo = NULL;
+	}
+
+	// XXX re-consider using callback API, testing needed.
+	err = Pa_OpenStream (
+			&_stream,
+			_capture_channels > 0 ? &inputParam: NULL,
+			_playback_channels > 0 ? &outputParam: NULL,
+			sample_rate,
+			samples_per_period,
+			paClipOff | paDitherOff,
+			NULL, NULL);
+
+	if (err != paNoError) {
+		fprintf(stderr, "PortAudio failed to start stream.\n");
+		goto error;
+	}
+
+	nfo_s = Pa_GetStreamInfo (_stream);
+	if (!nfo_s) {
+		fprintf(stderr, "PortAudio failed to query stream information.\n");
+		pcm_stop();
+		goto error;
+	}
+
+	_cur_sample_rate = nfo_s->sampleRate;
+	_cur_input_latency = nfo_s->inputLatency * _cur_sample_rate;
+	_cur_output_latency = nfo_s->outputLatency * _cur_sample_rate;
+
+#ifndef NDEBUG
+	printf("PA Sample Rate  %.1f SPS\n", _cur_sample_rate);
+	printf("PA Input Latency  %.1fms  %d spl\n", 1e3 * nfo_s->inputLatency, _cur_input_latency);
+	printf("PA Output Latency %.1fms  %d spl\n", 1e3 * nfo_s->outputLatency, _cur_output_latency);
+#endif
+
+	_state = 0;
+
+	if (_capture_channels > 0) {
+		_input_buffer = (float*) malloc (samples_per_period * _capture_channels * sizeof(float));
+		if (!_input_buffer) {
+			fprintf(stderr, "PortAudio failed to allocate input buffer.\n");
+			pcm_stop();
+			goto error;
+		}
+	}
+
+	if (_playback_channels > 0) {
+		_output_buffer = (float*) calloc (samples_per_period * _playback_channels, sizeof(float));
+		if (!_output_buffer) {
+			fprintf(stderr, "PortAudio failed to allocate output buffer.\n");
+			pcm_stop();
+			goto error;
+		}
+	}
+
+	return 0;
+
+error:
+	_capture_channels = 0;
+	_playback_channels = 0;
+	free (_input_buffer); _input_buffer = NULL;
+	free (_output_buffer); _output_buffer = NULL;
+	Pa_Terminate();
+	return -1;
+}
+
+int
+PortAudioIO::next_cycle (uint32_t n_samples)
+{
+	bool xrun = false;
+	PaError err;
+	err = Pa_IsStreamActive (_stream);
+	if (err != 1) {
+		//   0: inactive / aborted
+		// < 0: error
+		return -1;
+	}
+
+	// TODO, check drift..  process part with larger capacity first.
+	// Pa_GetStreamReadAvailable(_stream) < Pa_GetStreamWriteAvailable(_stream)
+
+	if (_playback_channels > 0) {
+		err = Pa_WriteStream (_stream, _output_buffer, n_samples);
+		if (err) xrun = true;
+	}
+
+	if (_capture_channels > 0) {
+		err = Pa_ReadStream (_stream, _input_buffer, n_samples);
+		if (err) {
+			memset (_input_buffer, 0, sizeof(float) * n_samples * _capture_channels);
+			xrun = true;
+		}
+	}
+
+
+	return xrun ? 1 : 0;
+}
+
+int
+PortAudioIO::get_capture_channel (uint32_t chn, float *input, uint32_t n_samples)
+{
+	assert(chn < _capture_channels);
+	const uint32_t stride = _capture_channels;
+	float *ptr = _input_buffer + chn;
+	while (n_samples-- > 0) {
+		*input++ = *ptr;
+		ptr += stride;
+	}
+	return 0;
+}
+
+int
+PortAudioIO::set_playback_channel (uint32_t chn, const float *output, uint32_t n_samples)
+{
+	assert(chn < _playback_channels);
+	const uint32_t stride = _playback_channels;
+	float *ptr = _output_buffer + chn;
+	while (n_samples-- > 0) {
+		*ptr = *output++;
+		ptr += stride;
+	}
+	return 0;
+}
diff --git a/libs/backends/portaudio/portaudio_io.h b/libs/backends/portaudio/portaudio_io.h
new file mode 100644
index 0000000000..532dc66df6
--- /dev/null
+++ b/libs/backends/portaudio/portaudio_io.h
@@ -0,0 +1,103 @@
+/*
+ * Copyright (C) 2015 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef __libbackend_portaudio_pcmio_h__
+#define __libbackend_portaudio_pcmio_h__
+
+#include <map>
+#include <vector>
+#include <string>
+#include <boost/shared_ptr.hpp>
+
+#include <stdint.h>
+
+#include <portaudio.h>
+
+namespace ARDOUR {
+
+class PortAudioIO {
+public:
+	PortAudioIO (void);
+	~PortAudioIO (void);
+
+	int      state (void) const { return _state; }
+
+	void     discover();
+	void     device_list (std::map<int, std::string> &devices) const;
+
+	int      available_sample_rates (int device_id, std::vector<float>& sampleRates);
+	int      available_buffer_sizes (int device_id, std::vector<uint32_t>& sampleRates);
+
+
+	void     pcm_stop (void);
+	int      pcm_start (void);
+
+	int      pcm_setup (
+			int device_input,
+			int device_output,
+			double   sample_rate,
+			uint32_t samples_per_period
+			);
+
+	uint32_t n_playback_channels (void) const { return _playback_channels; }
+	uint32_t n_capture_channels (void) const { return _capture_channels; }
+
+	double   sample_rate (void) const { return _cur_sample_rate; }
+	uint32_t capture_latency (void) const { return _cur_input_latency; }
+	uint32_t playback_latency (void) const { return _cur_output_latency; }
+	double   stream_time(void) const { if (_stream) return Pa_GetStreamTime (_stream); return 0; }
+
+	int      next_cycle(uint32_t n_samples);
+	int      get_capture_channel (uint32_t chn, float *input, uint32_t n_samples);
+	int      set_playback_channel (uint32_t chn, const float *input, uint32_t n_samples);
+
+private:
+	int  _state;
+	bool _initialized;
+
+	uint32_t _capture_channels;
+	uint32_t _playback_channels;
+
+	PaStream *_stream;
+
+	float *_input_buffer;
+	float *_output_buffer;
+
+	double _cur_sample_rate;
+	uint32_t _cur_input_latency;
+	uint32_t _cur_output_latency;
+
+
+	struct paDevice {
+		std::string name;
+		uint32_t n_inputs;
+		uint32_t n_outputs;
+
+		paDevice (std::string n, uint32_t i, uint32_t o)
+			: name (n)
+			, n_inputs (i)
+			, n_outputs (o)
+		{}
+	};
+
+	std::map<int, paDevice *> _devices;
+};
+
+} // namespace
+
+#endif /* __libbackend_portaudio_pcmio_h__ */
diff --git a/libs/backends/portaudio/rt_thread.h b/libs/backends/portaudio/rt_thread.h
new file mode 100644
index 0000000000..0535602bf2
--- /dev/null
+++ b/libs/backends/portaudio/rt_thread.h
@@ -0,0 +1,55 @@
+/*
+ * Copyright (C) 2014 Robin Gareus <robin@gareus.org>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
+ */
+
+#ifndef __libbackend_portaudio_rthread_h__
+#define __libbackend_portaudio_rthread_h__
+
+#include <pthread.h>
+#include <sched.h>
+
+static int
+_realtime_pthread_create (
+		const int policy, int priority, const size_t stacksize,
+		pthread_t *thread,
+		void *(*start_routine) (void *),
+		void *arg)
+{
+	int rv;
+
+	pthread_attr_t attr;
+	struct sched_param parm;
+
+	const int p_min = sched_get_priority_min (policy);
+	const int p_max = sched_get_priority_max (policy);
+	priority += p_max;
+	if (priority > p_max) priority = p_max;
+	if (priority < p_min) priority = p_min;
+	parm.sched_priority = priority;
+
+	pthread_attr_init (&attr);
+	pthread_attr_setschedpolicy (&attr, policy);
+	pthread_attr_setschedparam (&attr, &parm);
+	pthread_attr_setscope (&attr, PTHREAD_SCOPE_SYSTEM);
+	pthread_attr_setinheritsched (&attr, PTHREAD_EXPLICIT_SCHED);
+	pthread_attr_setstacksize (&attr, stacksize);
+	rv = pthread_create (thread, &attr, start_routine, arg);
+	pthread_attr_destroy (&attr);
+	return rv;
+}
+
+#endif
diff --git a/libs/backends/portaudio/wscript b/libs/backends/portaudio/wscript
new file mode 100644
index 0000000000..4b77f9670b
--- /dev/null
+++ b/libs/backends/portaudio/wscript
@@ -0,0 +1,35 @@
+#!/usr/bin/env python
+from waflib.extras import autowaf as autowaf
+from waflib import Options
+import os
+import sys
+import re
+
+I18N_PACKAGE = 'portaudio-backend'
+
+# Mandatory variables
+top = '.'
+out = 'build'
+
+def options(opt):
+    autowaf.set_options(opt)
+
+def configure(conf):
+    autowaf.configure(conf)
+    autowaf.check_pkg(conf, 'portaudio-2.0', uselib_store='PORTAUDIO', atleast_version='19')
+
+def build(bld):
+    obj = bld(features = 'cxx cxxshlib')
+    obj.source = [ 'portaudio_backend.cc',
+                   'portaudio_io.cc',
+#                  'portmidi_io.cc'
+                 ]
+    obj.includes = ['.']
+    obj.name     = 'portaudio_backend'
+    obj.target   = 'portaudio_backend'
+    obj.use      = 'libardour libpbd'
+    obj.uselib   = ['PORTAUDIO']
+    obj.install_path  = os.path.join(bld.env['LIBDIR'], 'backends')
+    obj.defines = ['PACKAGE="' + I18N_PACKAGE + '"',
+                   'ARDOURBACKEND_DLL_EXPORTS'
+                  ]