Correctly flush MIDI buffers on cycle-split

libs/ardour/audioengine.cc

@@ -146,11 +146,37 @@ AudioEngine::split_cycle (pframes_t offset)
 {
 	/* caller must hold process lock */
 
+	boost::shared_ptr<Ports> p = ports.reader();
+
+	/* This is mainly for the benefit of rt-control ports (MTC, MClk)
+	 *
+	 * Normally ports are flushed by the route:
+	 *   ARDOUR::MidiPort::flush_buffers(unsigned int)
+	 *   ARDOUR::Delivery::flush_buffers(long)
+	 *   ARDOUR::Route::flush_processor_buffers_locked(long)
+	 *   ARDOUR::Route::run_route(long, long, unsigned int, bool, bool)
+	 *   ...
+	 *
+	 * This is required so that route -> route connections work during
+	 * normal processing.
+	 *
+	 * However some non-route ports may contain MIDI events
+	 * from current Port::port_offset() .. Port::port_offset() + offset.
+	 * If those events are not pushed to ports before the cycle split,
+	 * MidiPort::flush_buffers will drop them (event time is out of bounds).
+	 *
+	 * TODO: for optimized builds MidiPort::flush_buffers() could
+	 * be relaxed, ignore ev->time() checks, and simply send
+	 * all events as-is.
+	 */
+	for (Ports::iterator i = p->begin(); i != p->end(); ++i) {
+		i->second->flush_buffers (offset);
+	}
+
 	Port::increment_global_port_buffer_offset (offset);
 
 	/* tell all Ports that we're going to start a new (split) cycle */
 
-	boost::shared_ptr<Ports> p = ports.reader();
 
 	for (Ports::iterator i = p->begin(); i != p->end(); ++i) {
 		i->second->cycle_split ();

libs/ardour/midi_port.cc

@@ -308,6 +308,9 @@ MidiPort::flush_buffers (pframes_t nframes)
 			}
 #endif
 
+			// XXX consider removing this check for optimized builds
+			// and just send 'em all, at cycle_end
+			// see AudioEngine::split_cycle (), PortManager::cycle_end()
 			if (   ev.time() >= _global_port_buffer_offset
 			    && ev.time() < _global_port_buffer_offset + nframes) {
 				pframes_t tme = floor (ev.time() / _speed_ratio);

libs/ardour/port_manager.cc

@@ -845,7 +845,9 @@ PortManager::cycle_end (pframes_t nframes, Session* s)
 	}
 
 	for (Ports::iterator p = _cycle_ports->begin(); p != _cycle_ports->end(); ++p) {
-		p->second->flush_buffers (nframes);
+		/* AudioEngine::split_cycle flushes buffers until Port::port_offset.
+		 * Now only flush remaining events (after Port::port_offset) */
+		p->second->flush_buffers (nframes - Port::port_offset ());
 	}
 
 	_cycle_ports.reset ();