fix one arg error; add delay to startup in example

adafruit_ble_midi.py

@@ -169,7 +169,7 @@ class MIDIService(Service):
                     if self._message_target_length:
                         self._pending_realtime = b
                     else:
-                        self._raw.write(b, self._header)
+                        self._raw.write(b, header=self._header)
                 else:
                     if (
                         0x80 <= data <= 0xBF or 0xE0 <= data <= 0xEF or data == 0xF2

examples/ble_midi_simpletest.py

@@ -33,6 +33,13 @@ while True:
     while not ble.connected:
         pass
     print("Connected")
+    # Sleep briefly so client can get ready and send setup
+    # writes to the MIDIService. 0.5secs was insufficient.
+    time.sleep(1.0)
+    # Send one unique NoteOn/Off at the beginning to check that the
+    # delay is sufficient.
+    midi.send(NoteOn(20, 99))
+    midi.send(NoteOff(20, 99))
     while ble.connected:
         midi.send(NoteOn(44, 120))  # G sharp 2nd octave
         time.sleep(0.25)