Add message bus listener removal handler for LevelDetectorSPL instance

Author: finneyj

model/MicroBit.cpp

@@ -201,6 +201,7 @@ int MicroBit::init()
     // which saves processor time, memeory and battery life.
     messageBus.listen(DEVICE_ID_MESSAGE_BUS_LISTENER, DEVICE_EVT_ANY, this, &MicroBit::onListenerRegisteredEvent);
     messageBus.listen(DEVICE_ID_MESSAGE_BUS_LISTENER, ID_PIN_P0, this, &MicroBit::onP0ListenerRegisteredEvent, MESSAGE_BUS_LISTENER_IMMEDIATE);
+    messageBus.listen(DEVICE_ID_MESSAGE_BUS_IGNORED, DEVICE_EVT_ANY, this, &MicroBit::onListenerRemovedEvent);
 
 #if CONFIG_ENABLED(DMESG_SERIAL_DEBUG) && DEVICE_DMESG_BUFFER_SIZE > 0
     codal_dmesg_set_flush_fn(microbit_dmesg_flush);
@@ -375,6 +376,22 @@ void MicroBit::onListenerRegisteredEvent(Event evt)
     }
 }
 
+/**
+  * A listener to perform actions as a result of Message Bus reflection.
+  *
+  * This callback is triggered upon a MessageBus listneer being removed.
+  * We may wish to perform cleanup operations as a result, etc.
+  *
+  */
+void MicroBit::onListenerRemovedEvent(Event evt)
+{
+    switch(evt.value)
+    {
+        case DEVICE_ID_SYSTEM_LEVEL_DETECTOR:
+        audio.levelSPL->listenerRemoved();
+        break;
+    }
+}
 
 /**
  * Perfom scheduler idle

model/MicroBit.h

@@ -122,6 +122,11 @@ namespace codal
              */
             void onP0ListenerRegisteredEvent(Event evt);
 
+            /**
+             * A callback listener to disable default audio streaming to P0 if an event handler is registered on that pin.
+             */
+            void onListenerRemovedEvent(Event evt);
+
             // Pin ranges used for LED matrix display.
 
         public: