sketch_oct30a.ino

const unsigned int LED{17}; // define a constant for the LED pin
const char S_OK { 0xaa };
const char S_ERR { 0xff };
void setup() {
  // put your setup code here, to run once:
  pinMode(LED, OUTPUT);

    // register "on_receive" as callback for RX event
    USBSerial.onEvent(ARDUINO_HW_CDC_RX_EVENT, on_receive);
    USBSerial.begin(9600);
}
void on_receive(void* event_handler_arg, esp_event_base_t event_base, int32_t event_id, void* event_data) { 
  
  char state { USBSerial.read() };

    // guard byte is valid LED state
  if (!(state == LOW || state == HIGH)) {
      // invalid byte received
      // report error
      USBSerial.write(S_ERR);
      return;
  }

  // update LED with valid state
  digitalWrite(LED, state);
  USBSerial.write(S_OK);
}
void loop() {
  // put your main code here, to run repeatedly:
}