usb-device-midi: Add additional console output on TX.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

micropython/usb/examples/device/midi_example.py

@@ -14,6 +14,16 @@ import time
 
 
 class MIDIExample(MIDIInterface):
+    # Very simple example event handler functions, showing how to receive note
+    # and control change messages sent from the host to the device.
+    #
+    # If you need to send MIDI data to the host, then it's fine to instantiate
+    # MIDIInterface class directly.
+
+    def on_open(self):
+        super().on_open()
+        print("Device opened by host")
+
     def on_note_on(self, channel, pitch, vel):
         print(f"RX Note On channel {channel} pitch {pitch} velocity {vel}")
 
@@ -35,17 +45,26 @@ while not m.is_open():
 
 print("Starting MIDI loop...")
 
+# TX constants
+CHANNEL = 0
+PITCH = 60
+CONTROLLER = 64
+
 control_val = 0
-channel = 0
 
 while m.is_open():
     time.sleep(1)
-    m.note_on(channel, 60)
+    print(f"TX Note On channel {CHANNEL} pitch {PITCH}")
+    m.note_on(CHANNEL, PITCH)  # Velocity is an optional third argument
     time.sleep(0.5)
-    m.note_off(channel, 60)
+    print(f"TX Note Off channel {CHANNEL} pitch {PITCH}")
+    m.note_off(CHANNEL, PITCH)
     time.sleep(1)
-    m.control_change(channel, 64, control_val)
+    print(f"TX Control channel {CHANNEL} controller {CONTROLLER} value {control_val}")
+    m.control_change(CHANNEL, CONTROLLER, control_val)
     control_val += 1
     if control_val == 0x7F:
         control_val = 0
     time.sleep(1)
+
+print("USB host has reset device, example done.")