ALSA: allow to select different I/O devices

This adds a basic support to use multiple sound-cards, currently
limited to two devices: In/Out with shared settings.

Advanced setups still have to resort to using the ARDOUR_ALSA_EXT
environment variable

2 files changed, 66 insertions, 30 deletions

diff --git a/libs/backends/alsa/alsa_audiobackend.cc b/libs/backends/alsa/alsa_audiobackend.cc
index 2efe2e8976..d8ceb7f796 100644
--- a/libs/backends/alsa/alsa_audiobackend.cc
+++ b/libs/backends/alsa/alsa_audiobackend.cc
@@ -782,10 +782,22 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 		return AudioDeviceInvalidError;
 	}
 
+	std::string slave_device;
+	AudioSlave::DuplexMode slave_duplex = AudioSlave::FullDuplex;
+
 	if (_input_audio_device != _output_audio_device) {
 		if (_input_audio_device != get_standard_device_name(DeviceNone) && _output_audio_device != get_standard_device_name(DeviceNone)) {
-			PBD::error << _("AlsaAudioBackend: Cannot use two different devices.");
-			return AudioDeviceInvalidError;
+#if 0 /* ideally we'd resample output ...*/
+			slave_device = _output_audio_device;
+			_output_audio_device = get_standard_device_name(DeviceNone);
+			slave_duplex = AudioSlave::HalfDuplexOut;
+#else
+			/*.. but input is usually a cheap USB device, and keeping
+			 * output does auto-connect master-out to the main device. */
+			slave_device = _input_audio_device;
+			_input_audio_device = get_standard_device_name(DeviceNone);
+			slave_duplex = AudioSlave::HalfDuplexIn;
+#endif
 		}
 		if (_input_audio_device != get_standard_device_name(DeviceNone)) {
 			get_alsa_audio_device_names(devices, HalfDuplexIn);
@@ -802,15 +814,14 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 		duplex = 3;
 	}
 
-	for (std::map<std::string, std::string>::const_iterator i = devices.begin (); i != devices.end(); ++i) {
-		if (i->first == audio_device) {
-			alsa_device = i->second;
-			break;
-		}
-	}
-	if (alsa_device == "") {
+	std::map<std::string, std::string>::const_iterator di = devices.find (audio_device);
+
+	if (di == devices.end ()) {
 		PBD::error << _("AlsaAudioBackend: Cannot find configured device. Is it still connected?");
 		return AudioDeviceNotAvailableError;
+	} else {
+		alsa_device = di->second;
+		assert (!alsa_device.empty());
 	}
 
 	_device_reservation.acquire_device(alsa_device.c_str());
@@ -954,26 +965,43 @@ AlsaAudioBackend::_start (bool for_latency_measurement)
 
 	_midi_device_thread_active = listen_for_midi_device_changes ();
 
+	if (!slave_device.empty () && (di = devices.find (slave_device)) != devices.end ()) {
+		std::string dev = di->second;
+		if (add_slave (dev.c_str(), _samplerate, _samples_per_period, _periods_per_cycle, slave_duplex)) {
+			PBD::info << string_compose (_("ALSA slave '%1' added"), dev) << endmsg;
+		} else {
+			PBD::error << string_compose (_("ALSA failed to add '%1' as slave"), dev) << endmsg;
+		}
+	}
+
 #if 1 // TODO: we need a GUI (and API) for this
+	/* example: ARDOUR_ALSA_EXT="hw:2@48000/512*3;hw:3@44100" */
 	if (NULL != getenv ("ARDOUR_ALSA_EXT")) {
 		boost::char_separator<char> sep (";");
-		boost::tokenizer<boost::char_separator<char> > devs (std::string(getenv ("ARDOUR_ALSA_EXT")), sep);
+		std::string ext (getenv ("ARDOUR_ALSA_EXT"));
+		boost::tokenizer<boost::char_separator<char> > devs (ext, sep);
 		BOOST_FOREACH (const std::string& tmp, devs) {
 			std::string dev (tmp);
-			std::string::size_type n = dev.find ('@');
 			unsigned int sr = _samplerate;
 			unsigned int spp = _samples_per_period;
-			unsigned int duplex = 3; // TODO parse 1: play, 2: capt, 3:both
+			unsigned int ppc = _periods_per_cycle;
+			AudioSlave::DuplexMode duplex = AudioSlave::FullDuplex;
+			std::string::size_type n = dev.find ('@');
 			if (n != std::string::npos) {
-				std::string opt (dev.substr (n + 1));
+				std::string const opt (dev.substr (n + 1));
 				sr = PBD::atoi (opt);
 				dev = dev.substr (0, n);
 				std::string::size_type n = opt.find ('/');
 				if (n != std::string::npos) {
-					spp = PBD::atoi (opt.substr (n + 1));
+					std::string const opt2 (opt.substr (n + 1));
+					spp = PBD::atoi (opt2);
+					std::string::size_type n = opt2.find ('*');
+					if (n != std::string::npos) {
+						ppc = PBD::atoi (opt2.substr (n + 1));
+					}
 				}
 			}
-			if (add_slave (dev.c_str(), sr, spp, duplex)) {
+			if (add_slave (dev.c_str(), sr, spp, ppc, duplex)) {
 				PBD::info << string_compose (_("ALSA slave '%1' added"), dev) << endmsg;
 			} else {
 				PBD::error << string_compose (_("ALSA failed to add '%1' as slave"), dev) << endmsg;
@@ -2007,11 +2035,12 @@ bool
 AlsaAudioBackend::add_slave (const char*  device,
                              unsigned int slave_rate,
                              unsigned int slave_spp,
-                             unsigned int duplex)
+                             unsigned int slave_ppc,
+                             AudioSlave::DuplexMode duplex)
 {
 	AudioSlave* s = new AudioSlave (device, duplex,
 			_samplerate, _samples_per_period,
-			slave_rate, slave_spp, 2);
+			slave_rate, slave_spp, slave_ppc);
 
 	if (s->state ()) {
 		// TODO parse error status
@@ -2064,18 +2093,18 @@ errout:
 
 AlsaAudioBackend::AudioSlave::AudioSlave (
 		const char*  device,
-		unsigned int duplex,
+		DuplexMode   duplex,
 		unsigned int master_rate,
 		unsigned int master_samples_per_period,
 		unsigned int slave_rate,
 		unsigned int slave_samples_per_period,
-		unsigned int periods_per_cycle)
+		unsigned int slave_periods_per_cycle)
 	: AlsaDeviceReservation (device)
 	, AlsaAudioSlave (
-			(duplex & 1) ? device : NULL /* playback */,
-			(duplex & 2) ? device : NULL /* capture */,
+			(duplex & HalfDuplexOut) ? device : NULL /* playback */,
+			(duplex & HalfDuplexIn)  ? device : NULL /* capture */,
 			master_rate, master_samples_per_period,
-			slave_rate, slave_samples_per_period, periods_per_cycle)
+			slave_rate, slave_samples_per_period, slave_periods_per_cycle)
 	, active (false)
 	, halt (false)
 	, dead (false)
diff --git a/libs/backends/alsa/alsa_audiobackend.h b/libs/backends/alsa/alsa_audiobackend.h
index 49afd7e34e..02d61c6042 100644
--- a/libs/backends/alsa/alsa_audiobackend.h
+++ b/libs/backends/alsa/alsa_audiobackend.h
@@ -130,7 +130,7 @@ class AlsaAudioBackend : public AudioBackend, public PortEngineSharedImpl
 		bool is_realtime () const;
 
 		bool use_separate_input_and_output_devices () const { return true; }
-		bool match_input_output_devices_or_none () const { return true; }
+		bool match_input_output_devices_or_none () const { return false; }
 		bool can_set_period_size () const { return true; }
 
 		std::vector<DeviceStatus> enumerate_devices () const;
@@ -399,17 +399,17 @@ class AlsaAudioBackend : public AudioBackend, public PortEngineSharedImpl
 		void update_systemic_audio_latencies ();
 		void update_systemic_midi_latencies ();
 
-		/* additional re-sampled I/O */
-		bool add_slave (const char*  slave_device,
-		                unsigned int slave_rate,
-		                unsigned int slave_spp,
-		                unsigned int duplex = 3);
-
 		class AudioSlave : public AlsaDeviceReservation, public AlsaAudioSlave {
 			public:
+				enum DuplexMode {
+					HalfDuplexIn  = 1,
+					HalfDuplexOut = 2,
+					FullDuplex    = 3
+				};
+
 				AudioSlave (
 						const char*  device,
-						unsigned int duplex,
+						DuplexMode   duplex,
 						unsigned int master_rate,
 						unsigned int master_samples_per_period,
 						unsigned int slave_rate,
@@ -436,6 +436,13 @@ class AlsaAudioBackend : public AudioBackend, public PortEngineSharedImpl
 				void halted ();
 		};
 
+		/* additional re-sampled I/O */
+		bool add_slave (const char*  slave_device,
+		                unsigned int slave_rate,
+		                unsigned int slave_spp,
+		                unsigned int slave_ppc,
+										AudioSlave::DuplexMode);
+
 		typedef std::vector<AudioSlave*> AudioSlaves;
 		AudioSlaves _slaves;