add loopback example

Author: facchinm

examples/MIDIUSB_loop/MIDIUSB_loop.ino

@@ -0,0 +1,54 @@
+/*
+ * MIDIUSB_loop.ino
+ *
+ * Created: 4/6/2015 10:47:08 AM
+ * Author: gurbrinder grewal
+ * Modified by Arduino LLC (2015)
+ */ 
+
+#include "MIDIUSB.h"
+
+// First parameter is the event type (0x09 = note on, 0x08 = note off).
+// Second parameter is note-on/note-off, combined with the channel.
+// Channel can be anything between 0-15. Typically reported to the user as 1-16.
+// Third parameter is the note number (48 = middle C).
+// Fourth parameter is the velocity (64 = normal, 127 = fastest).
+
+void noteOn(byte channel, byte pitch, byte velocity) {
+  midiEventPacket_t noteOn = {0x09, 0x90 | channel, pitch, velocity};
+  MidiUSB.sendMIDI(noteOn);
+}
+
+void noteOff(byte channel, byte pitch, byte velocity) {
+  midiEventPacket_t noteOff = {0x08, 0x80 | channel, pitch, velocity};
+  MidiUSB.sendMIDI(noteOff);
+}
+
+void setup() {
+  Serial.begin(115200);
+  pinMode(LED_BUILTIN, OUTPUT);
+}
+
+// First parameter is the event type (0x0B = control change).
+// Second parameter is the event type, combined with the channel.
+// Third parameter is the control number number (0-119).
+// Fourth parameter is the control value (0-127).
+
+void controlChange(byte channel, byte control, byte value) {
+  midiEventPacket_t event = {0x0B, 0xB0 | channel, control, value};
+  MidiUSB.sendMIDI(event);
+}
+
+void loop() {
+  //MidiUSB.accept();
+  //delayMicroseconds(1);
+  midiEventPacket_t rx;
+  do {
+    rx = MidiUSB.read();
+    if (rx.header != 0) {
+      //send back the received MIDI command
+      MidiUSB.sendMIDI(rx);
+      MidiUSB.flush();
+    }
+  } while (rx.header != 0);
+}