BLE Midi roundtrip latency info

Author: JorenSix

README.md

@@ -117,6 +117,10 @@ This application sends out a MIDI message as quickly as possible when a MIDI mes
 ![MIDI round trip latency](misc/round_trip.webp "Round_trip latency measurement")
 
 
+The roundtrip time for a midi message send over BTLE is much worse: with an ESP32 I measured  an average of 43 +-	6 milliseconds with the worst rountrip time around 60 ms. There is also a BT LE MIDI 
+
+
+
 ## Browser to OSC example
 
 One of the ways to send OSC messages from a browser to a local network is by using the MIDI out capability of browsers and - using `mot` - translating MIDI to OSC an example can be seen below.

misc/midi_roundtrip_latency_blemidi_esp32/midi_roundtrip_latency_blemidi_esp32.ino

@@ -0,0 +1,51 @@
+#define LED 2
+#include <BLEMidi.h>
+
+hw_timer_t *timer = NULL;
+
+boolean sendMidi = false;
+
+unsigned long midiMessagSendTime = 0;
+
+void ARDUINO_ISR_ATTR onTimer(){
+  // Increment the counter and set the time of ISR
+  sendMidi = true;
+  digitalWrite(LED, !digitalRead(LED));
+}
+
+void onNoteOn(uint8_t channel, uint8_t note, uint8_t velocity, uint16_t timestamp){
+  unsigned long midiMessageReceiveTime = micros();
+  unsigned long roundtripMidiMessageTime  =  midiMessageReceiveTime - midiMessagSendTime;
+  Serial.printf("Received note on : round trip time %d microsecond\n", roundtripMidiMessageTime);
+}
+
+void setup() {
+  pinMode(LED, OUTPUT);
+
+  //set timer callback function
+  timer = timerBegin(1000000);
+  // Attach onTimer function to our timer.
+  timerAttachInterrupt(timer, &onTimer);
+  // Set alarm to call onTimer function every second (value in microseconds).
+  // Repeat the alarm (third parameter) with unlimited count = 0 (fourth parameter).
+  timerAlarm(timer, 1000000, true, 0);
+
+  Serial.begin(115200);
+  Serial.println("Initializing bluetooth");
+
+  BLEMidiServer.begin("MIDI_Roundtrip"); 
+  BLEMidiServer.setNoteOnCallback(onNoteOn);
+  while( ! BLEMidiServer.isConnected() ){
+    Serial.println("Waiting for BLE MIDI connection...");
+    delay(1000);
+  }
+}
+
+void loop() {
+  if(sendMidi){
+    sendMidi = false;
+    midiMessagSendTime = micros();
+    BLEMidiServer.noteOn(0, 69, 127);
+    Serial.println("Midi Message send");
+  }
+}