USBSerial.ino

#ifndef ARDUINO_USB_MODE
#error This ESP32 SoC has no Native USB interface
#elif ARDUINO_USB_MODE == 1
#warning This sketch should be used when USB is in OTG mode
void setup() {}
void loop() {}
#else
#include "USB.h"

#if !ARDUINO_USB_CDC_ON_BOOT
USBCDC USBSerial;
#endif

static void usbEventCallback(void *arg, esp_event_base_t event_base, int32_t event_id, void *event_data) {
  if (event_base == ARDUINO_USB_EVENTS) {
    arduino_usb_event_data_t *data = (arduino_usb_event_data_t *)event_data;
    switch (event_id) {
      case ARDUINO_USB_STARTED_EVENT: Serial.println("USB PLUGGED"); break;
      case ARDUINO_USB_STOPPED_EVENT: Serial.println("USB UNPLUGGED"); break;
      case ARDUINO_USB_SUSPEND_EVENT: Serial.printf("USB SUSPENDED: remote_wakeup_en: %u\n", data->suspend.remote_wakeup_en); break;
      case ARDUINO_USB_RESUME_EVENT:  Serial.println("USB RESUMED"); break;

      default: break;
    }
  } else if (event_base == ARDUINO_USB_CDC_EVENTS) {
    arduino_usb_cdc_event_data_t *data = (arduino_usb_cdc_event_data_t *)event_data;
    switch (event_id) {
      case ARDUINO_USB_CDC_CONNECTED_EVENT:    Serial.println("CDC CONNECTED"); break;
      case ARDUINO_USB_CDC_DISCONNECTED_EVENT: Serial.println("CDC DISCONNECTED"); break;
      case ARDUINO_USB_CDC_LINE_STATE_EVENT:   Serial.printf("CDC LINE STATE: dtr: %u, rts: %u\n", data->line_state.dtr, data->line_state.rts); break;
      case ARDUINO_USB_CDC_LINE_CODING_EVENT:
        Serial.printf(
          "CDC LINE CODING: bit_rate: %lu, data_bits: %u, stop_bits: %u, parity: %u\n", data->line_coding.bit_rate, data->line_coding.data_bits,
          data->line_coding.stop_bits, data->line_coding.parity
        );
        break;
      case ARDUINO_USB_CDC_RX_EVENT:
        Serial.printf("CDC RX [%u]:", data->rx.len);
        {
          uint8_t buf[data->rx.len];
          size_t len = USBSerial.read(buf, data->rx.len);
          Serial.write(buf, len);
        }
        Serial.println();
        break;
      case ARDUINO_USB_CDC_RX_OVERFLOW_EVENT: Serial.printf("CDC RX Overflow of %d bytes", data->rx_overflow.dropped_bytes); break;

      default: break;
    }
  }
}

void setup() {
  Serial.begin(115200);
  Serial.setDebugOutput(true);

  USB.onEvent(usbEventCallback);
  USBSerial.onEvent(usbEventCallback);

  USBSerial.begin();
  USB.begin();
}

void loop() {
  while (Serial.available()) {
    size_t l = Serial.available();
    uint8_t b[l];
    l = Serial.read(b, l);
    USBSerial.write(b, l);
  }
}
#endif /* ARDUINO_USB_MODE */