void setup() {
  // USB serial monitor
  Serial.begin(115200);
  delay(1000);

  Serial.println("Starting UART loopback test");

  // UART1 on Raspberry Pi Pico:
  // TX = GP8, RX = GP9
  Serial1.setTX(8);
  Serial1.setRX(9);
  Serial1.begin(9600);

  // Clear old data
  while (Serial1.available()) {
    Serial1.read();
  }

  // Send message
  Serial1.print("Hello Wokwi\n");
  Serial.println("Sent: Hello Wokwi");

  delay(500);

  // Read back looped data
  String received = "";
  while (Serial1.available()) {
    char c = Serial1.read();
    received += c;
  }

  if (received.length() > 0) {
    received.trim();
    Serial.print("Received: ");
    Serial.println(received);
  } else {
    Serial.println("No data received");
  }
}

void loop() {
}