limit frequency of reading & parsing MIDI data

To improve note accuracy

main.cpp

@@ -5,6 +5,10 @@
 
 #define NUM_MOTORS 4
 
+// Minimal interval between reading two chunks of MIDI data
+// This improves frequency accuracy by throttling non-synthesizing actions
+#define MIDI_CMD_INTERVAL_MIN 15 * 1000 // 15ms
+
 using namespace midi;
 
 MotorControl motors[NUM_MOTORS] = {
@@ -73,10 +77,24 @@ int main() {
     MIDI.setHandleNoteOn(midi_note_on);
     MIDI.setHandleNoteOff(midi_note_off);
 
+    unsigned long cur_micros;
+    unsigned long last_read_micros = 0;
+
     while (true) {
-        unsigned long cur_micros = timer2.get_count() / 2ul; // The unit of get_count is 0.5us
+        cur_micros = timer2.get_count() / 2ul; // The unit of get_count is 0.5us
         handle_tick(cur_micros);
-        MIDI.read();
+
+        if (cur_micros - last_read_micros >= MIDI_CMD_INTERVAL_MIN) {
+            last_read_micros = cur_micros;
+
+            // Read all available MIDI data
+            // Note that the host is expected to send MIDI data only when
+            // it is supposed to be played; therefore we don't need
+            // to worry about the host sending data prematurely
+            while (Serial.available()) {
+                MIDI.read();
+            }
+        }
     }
 
     return 0;