Added information on demand-wake for the audio pipeline and fixed the wake-up sequence

Author: JohnVidler

source/MicroBitAudio.cpp

@@ -63,6 +63,16 @@ MicroBitAudio::MicroBitAudio(NRF52Pin &pin, NRF52Pin &speaker, NRF52ADC &adc, NR
     adc.setSamplePeriod( 1e6 / 22000 );
     mic->setGain(7,0);
 
+    // Implementers note: The order that the pipeline comes up here is quite senitive. If we connect up to splitters after starting to
+    // listen for events from them, we'll see channel startup events (which are valid!) that we don't want. So roughly always follow
+    // the following schema:
+    //
+    // 1. Create the splitter
+    // 2. Attach any stages to the splitter
+    // 3. Start listening for splitter events
+    //
+    // This prevents any cases where the pipeline stages cause a connect() message to be emitted, which then auto-activates the mic.
+
     //Initialialise the microphone filter
     micFilter = new LowPassFilter(mic->output, 0.1f, true);
 
@@ -72,6 +82,10 @@ MicroBitAudio::MicroBitAudio(NRF52Pin &pin, NRF52Pin &speaker, NRF52ADC &adc, NR
     //Initilise stream normalizer
     processor = new StreamNormalizer(*rawSplitter->createChannel(), 0.08f, true, DATASTREAM_FORMAT_8BIT_SIGNED, 10);
 
+    // Connect to the rawSplitter. This must come AFTER the processor, to prevent the processor's channel activation starting the microphone
+    if(EventModel::defaultEventBus)
+        EventModel::defaultEventBus->listen(rawSplitter->id, DEVICE_EVT_ANY, this, &MicroBitAudio::onSplitterEvent, MESSAGE_BUS_LISTENER_IMMEDIATE);
+
     //Initilise stream splitter
     splitter = new StreamSplitter(processor->output, DEVICE_ID_SPLITTER);
 
@@ -81,21 +95,22 @@ MicroBitAudio::MicroBitAudio(NRF52Pin &pin, NRF52Pin &speaker, NRF52ADC &adc, NR
     //Initilise level detector SPL and attach to splitter
     levelSPL = new LevelDetectorSPL(*rawSplitter->createChannel(), 85.0, 65.0, 16.0, 0, DEVICE_ID_MICROPHONE, false);
 
-    // Register listener for splitter events
-    if(EventModel::defaultEventBus){
-        EventModel::defaultEventBus->listen(rawSplitter->id, DEVICE_EVT_ANY, this, &MicroBitAudio::onSplitterEvent, MESSAGE_BUS_LISTENER_IMMEDIATE);
+    // Connect to the splitter - this COULD come after we create it, before we add any stages, as these are dynamic and will only connect on-demand, but just in case
+    // we're going to follow the schema set out above, to be 100% sure.
+    if(EventModel::defaultEventBus)
         EventModel::defaultEventBus->listen(DEVICE_ID_SPLITTER, DEVICE_EVT_ANY, this, &MicroBitAudio::onSplitterEvent, MESSAGE_BUS_LISTENER_IMMEDIATE);
-    }
 }
 
 /**
  * Handle events from splitter
  */
 void MicroBitAudio::onSplitterEvent(MicroBitEvent e){
-    if(e.value == SPLITTER_ACTIVATE_CHANNEL)
+    if( e.value == SPLITTER_CHANNEL_CONNECT )
         activateMic();
-    else if (e.value == SPLITTER_DEACTIVATE_CHANNEL)
-        if( splitter->numberChannels <= 0 && rawSplitter->numberChannels <= 0 ) // Only deactivate if we have no more channels to serve!
+    
+    // Note: The processor will always be present on the rawSplitter, hence the <= 1.
+    else if( e.value == SPLITTER_CHANNEL_DISCONNECT )
+        if( splitter->numberActiveChannels <= 0 && rawSplitter->numberActiveChannels <= 1 )
             deactivateMic();
 }