change esp32 example to avoid freezes over serial usage on isr

examples/ESP32UartMasterMidiClock/ESP32UartMasterMidiClock.ino

@@ -18,6 +18,8 @@
 // the blue led
 #define LED_BUILTIN    2
 
+volatile bool _midi_clk_income = false;
+
 uint8_t bpm_blink_timer = 1;
 void handle_bpm_led(uint32_t tick)
 {
@@ -37,6 +39,7 @@ void handle_bpm_led(uint32_t tick)
 void ClockOut96PPQN(uint32_t tick) {
   // Send MIDI_CLOCK to external gears
   //Serial.write(MIDI_CLOCK);
+  _midi_clk_income = true;
   handle_bpm_led(tick);
 }
 
@@ -71,5 +74,11 @@ void setup() {
 
 // Do it whatever to interface with Clock.stop(), Clock.start(), Clock.setTempo() and integrate your environment...
 void loop() {
-
+  // watch for income signal from uClock to fire the clock over midi
+  if (_midi_clk_income) {
+    Serial.write(MIDI_CLOCK);
+    noInterrupts();
+    _midi_clk_income = false;
+    interrupts();
+  }
 }