Expose BLE-MIDI server as a local ALSA sequencer

Author: arkq

.github/iwyu.imp

@@ -5,6 +5,7 @@
 	{ include: [ '<bsd/libutil.h>', private, '<bsd/stdlib.h>', public ] },
 	{ include: [ '<bsd/sys/time.h>', private, '<sys/time.h>', public ] },
 	{ symbol: [ 'sig_atomic_t', private, '<signal.h>', public ] },
+	{ symbol: [ 'S_IRWXU', private, '<sys/stat.h>', public ] },
 
 	{ include: [ '<alsa/conf.h>', private, '<alsa/asoundlib.h>', public ] },
 	{ include: [ '<alsa/control.h>', private, '<alsa/asoundlib.h>', public ] },
@@ -15,6 +16,10 @@
 	{ include: [ '<alsa/output.h>', private, '<alsa/asoundlib.h>', public ] },
 	{ include: [ '<alsa/pcm.h>', private, '<alsa/asoundlib.h>', public ] },
 	{ include: [ '<alsa/pcm_ioplug.h>', private, '<alsa/pcm_external.h>', public ] },
+	{ include: [ '<alsa/seq.h>', private, '<alsa/asoundlib.h>', public ] },
+	{ include: [ '<alsa/seq_event.h>', private, '<alsa/asoundlib.h>', public ] },
+	{ include: [ '<alsa/seq_midi_event.h>', private, '<alsa/asoundlib.h>', public ] },
+	{ include: [ '<alsa/seqmid.h>', private, '<alsa/asoundlib.h>', public ] },
 	{ include: [ '<alsa/version.h>', private, '<alsa/asoundlib.h>', public ] },
 
 	{ include: [ '"dbus/dbus-memory.h"', private, '<dbus/dbus.h>', public ] },

NEWS

@@ -1,6 +1,7 @@
 unreleased
 ==========
 
+- optional support for BLE MIDI 1.0 profile as a GATT server
 - command line option to set real-time priority for IO threads
 - allow to select individual extended controls in ALSA plug-in
 - codec-specific delay adjustment with ALSA control and persistency

README.md

@@ -34,7 +34,7 @@ ALSA, with only one application at a time using each Bluetooth audio stream.
 In such systems BlueALSA adds Bluetooth audio support to the existing
 ALSA sound card support. Note this means that the applications are constrained
 by the capabilities of the ALSA API, and the higher-level audio processing
-features of audio servers such as PulseAudio and Pipewire are not available.
+features of audio servers such as PulseAudio and PipeWire are not available.
 
 BlueALSA consists of the daemon `bluealsa`, ALSA plug-ins, and a number of
 utilities. The basic context is shown in this diagram:
@@ -55,8 +55,11 @@ C <--> G((bluealsa-cli))
 F <--> H([ALSA libasound])
 H <--> I((ALSA\napplications))
 C <--> J((other\nD-Bus clients))
+C <--> L((ALSA MIDI\nsequencer))
+L <--> M([ALSA libasound])
+M <--> N((ALSA MIDI\napplication))
 
-class A,B,E,H,I,J,K external;
+class A,B,E,H,I,J,K,L,M,N external;
 class C,D,F,G bluealsa;
 ```
 
@@ -70,6 +73,10 @@ applications to use the ALSA PCM and mixer interfaces, so that existing ALSA
 applications can access Bluetooth audio devices in the same way as they use
 sound card PCMs and mixers.
 
+In case of BLE MIDI, the daemon creates a simple MIDI port directly in ALSA
+MIDI sequencer, so that ALSA MIDI application can connect to the remote BLE
+MIDI device in the same way as it would connect to a local MIDI device.
+
 BlueALSA also includes a number of utility applications. Of particular note
 are:
 
@@ -239,7 +246,7 @@ If reporting a problem as a new issue, please use the appropriate
 [bluez-alsa GitHub issue reporting template][] and complete each section of
 the template as fully as possible.
 
-[TROUBLESHOOTING]: ./TROUBLESHOOTING.md
+[TROUBLESHOOTING]: TROUBLESHOOTING.md
 [manual pages]: doc/
 [previous issues]: https://github.com/arkq/bluez-alsa/issues
 [wiki]: https://github.com/arkq/bluez-alsa/wiki

src/Makefile.am

@@ -85,7 +85,9 @@ endif
 
 if ENABLE_MIDI
 bluealsa_SOURCES += \
-	bluez-midi.c
+	ble-midi.c \
+	bluez-midi.c \
+	midi.c
 endif
 
 if ENABLE_MPEG
@@ -111,6 +113,7 @@ endif
 
 AM_CFLAGS = \
 	@AAC_CFLAGS@ \
+	@ALSA_CFLAGS@ \
 	@APTX_CFLAGS@ \
 	@APTX_HD_CFLAGS@ \
 	@BLUEZ_CFLAGS@ \
@@ -127,6 +130,7 @@ AM_CFLAGS = \
 
 LDADD = \
 	@AAC_LIBS@ \
+	@ALSA_LIBS@ \
 	@APTX_HD_LIBS@ \
 	@APTX_LIBS@ \
 	@BLUEZ_LIBS@ \

src/ba-transport.c

@@ -25,6 +25,7 @@
 #include <sys/time.h>
 #include <unistd.h>
 
+#include <alsa/asoundlib.h>
 #include <bluetooth/bluetooth.h>
 #include <bluetooth/hci.h>
 
@@ -42,6 +43,7 @@
 #include "bluez.h"
 #include "hci.h"
 #include "hfp.h"
+#include "midi.h"
 #include "sco.h"
 #include "storage.h"
 #include "shared/defs.h"
@@ -597,12 +599,13 @@ struct ba_transport *ba_transport_new_sco(
 #if ENABLE_MIDI
 
 static int transport_acquire_bt_midi(struct ba_transport *t) {
-	(void)t;
-	return 0;
+	return midi_transport_alsa_seq_create(t);
 }
 
 static int transport_release_bt_midi(struct ba_transport *t) {
 
+	midi_transport_alsa_seq_delete(t);
+
 	if (t->midi.ble_fd_write != -1) {
 		debug("Releasing BLE-MIDI write link: %d", t->midi.ble_fd_write);
 		close(t->midi.ble_fd_write);
@@ -630,10 +633,28 @@ struct ba_transport *ba_transport_new_midi(
 
 	t->profile = profile;
 
+	t->midi.seq_port = -1;
+	t->midi.ble_fd_write = -1;
+	t->midi.ble_fd_notify = -1;
+
+	int err;
+	if ((err = snd_midi_event_new(1024, &t->midi.seq_parser)) < 0) {
+		error("Couldn't create MIDI event decoder: %s", snd_strerror(err));
+		goto fail;
+	}
+
+	/* Disable MIDI running status generated by the decoder. */
+	snd_midi_event_no_status(t->midi.seq_parser, 1);
+
 	t->acquire = transport_acquire_bt_midi;
 	t->release = transport_release_bt_midi;
 
 	return t;
+
+fail:
+	ba_transport_unref(t);
+	errno = -err;
+	return NULL;
 }
 
 #endif
@@ -821,6 +842,12 @@ void ba_transport_unref(struct ba_transport *t) {
 		free(t->sco.ofono_dbus_path_modem);
 #endif
 	}
+#if ENABLE_MIDI
+	else if (t->profile & BA_TRANSPORT_PROFILE_MIDI) {
+		if (t->midi.seq_parser != NULL)
+			snd_midi_event_free(t->midi.seq_parser);
+	}
+#endif
 
 	if (t->thread_manager_pipe[0] != -1)
 		close(t->thread_manager_pipe[0]);
@@ -989,6 +1016,11 @@ void ba_transport_set_codec(
  *   errno is set to indicate the error. */
 int ba_transport_start(struct ba_transport *t) {
 
+#if ENABLE_MIDI
+	if (t->profile & BA_TRANSPORT_PROFILE_MIDI)
+		return midi_transport_start(t);
+#endif
+
 	/* For A2DP Source profile only, it is possible that BlueZ will
 	 * activate the transport following a D-Bus "Acquire" request before the
 	 * client thread has completed the acquisition procedure by initializing
@@ -1033,6 +1065,11 @@ int ba_transport_start(struct ba_transport *t) {
  * to call it from IO thread itself - it will cause deadlock! */
 int ba_transport_stop(struct ba_transport *t) {
 
+#if ENABLE_MIDI
+	if (t->profile & BA_TRANSPORT_PROFILE_MIDI)
+		return midi_transport_stop(t);
+#endif
+
 	if (t->profile & BA_TRANSPORT_PROFILE_MASK_A2DP) {
 		if (ba_transport_pcm_state_check_terminated(&t->a2dp.pcm) &&
 				ba_transport_pcm_state_check_terminated(&t->a2dp.pcm_bc))
@@ -1110,6 +1147,11 @@ int ba_transport_stop_if_no_clients(struct ba_transport *t) {
 
 int ba_transport_acquire(struct ba_transport *t) {
 
+#if ENABLE_MIDI
+	if (t->profile & BA_TRANSPORT_PROFILE_MIDI)
+		return t->acquire(t);
+#endif
+
 	bool acquired = false;
 	int fd = -1;
 
@@ -1165,6 +1207,11 @@ int ba_transport_acquire(struct ba_transport *t) {
 
 int ba_transport_release(struct ba_transport *t) {
 
+#if ENABLE_MIDI
+	if (t->profile & BA_TRANSPORT_PROFILE_MIDI)
+		return t->release(t);
+#endif
+
 	int ret = 0;
 
 	pthread_mutex_lock(&t->bt_fd_mtx);

src/ba-transport.h

@@ -22,9 +22,13 @@
 #include <stdint.h>
 #include <time.h>
 
+#include <alsa/asoundlib.h>
+#include <glib.h>
+
 #include "a2dp.h"
 #include "ba-device.h"
 #include "ba-transport-pcm.h"
+#include "ble-midi.h"
 #include "bluez.h"
 #include "shared/a2dp-codecs.h"
 
@@ -172,11 +176,29 @@ struct ba_transport {
 #if ENABLE_MIDI
 		struct {
 
+			/* ALSA sequencer. */
+			snd_seq_t *seq;
+			/* Associated sequencer port. */
+			int seq_port;
+
+			/* ALSA MIDI event parser. */
+			snd_midi_event_t *seq_parser;
+
 			/* BLE-MIDI input link */
 			int ble_fd_write;
 			/* BLE-MIDI output (notification) link */
 			int ble_fd_notify;
 
+			/* BLE-MIDI parser for the incoming data. */
+			struct ble_midi_dec ble_decoder;
+			/* BLE-MIDI parser for the outgoing data. */
+			struct ble_midi_enc ble_encoder;
+
+			/* Watch associated with the BLE-MIDI link. */
+			GSource *watch_ble;
+			/* Watch associated with ALSA sequencer. */
+			GSource *watch_seq;
+
 		} midi;
 #endif
 

src/bluez-midi.c

@@ -35,9 +35,11 @@
 #include "ba-adapter.h"
 #include "ba-device.h"
 #include "ba-transport.h"
+#include "ble-midi.h"
 #include "bluealsa-config.h"
 #include "bluez-iface.h"
 #include "dbus.h"
+#include "midi.h"
 #include "utils.h"
 #include "shared/bluetooth.h"
 #include "shared/defs.h"
@@ -208,6 +210,8 @@ static void bluez_midi_characteristic_acquire_write(
 
 	/* TODO: Find a way to detect "device" disconnection condition. */
 
+	midi_transport_start_watch_ble_midi(t);
+
 	GUnixFDList *fd_list = g_unix_fd_list_new_from_array(&fds[1], 1);
 	g_dbus_method_invocation_return_value_with_unix_fd_list(inv,
 			g_variant_new("(hq)", 0, mtu), fd_list);
@@ -262,6 +266,7 @@ static void bluez_midi_characteristic_acquire_notify(
 	debug("New BLE-MIDI notify link (MTU: %u): %d", mtu, fds[0]);
 	app->notify_acquired = true;
 	t->midi.ble_fd_notify = fds[0];
+	ble_midi_encode_set_mtu(&t->midi.ble_encoder, mtu);
 	t->mtu_write = mtu;
 
 	/* Setup IO watch for checking HUP condition on the socket. HUP means
@@ -384,6 +389,8 @@ GDBusObjectManagerServer *bluez_midi_app_new(
 		error("Couldn't create local MIDI transport: %s", strerror(errno));
 	else if (ba_transport_acquire(t) == -1)
 		error("Couldn't acquire local MIDI transport: %s", strerror(errno));
+	else if (ba_transport_start(t) == -1)
+		error("Couldn't start local MIDI transport: %s", strerror(errno));
 	app->t = t;
 
 	GDBusObjectManagerServer *manager = g_dbus_object_manager_server_new(path);