Connects to the J-Link emulator (over SEGGER tunnel).

        Args:
          self (JLink): the ``JLink`` instance
          serial_no (int): serial number of the J-Link
          port (int): optional port number (default to 19020).

        Returns:
          ``None``

def open_tunnel(self, serial_no, port=19020):
        """Connects to the J-Link emulator (over SEGGER tunnel).

        Args:
          self (JLink): the ``JLink`` instance
          serial_no (int): serial number of the J-Link
          port (int): optional port number (default to 19020).

        Returns:
          ``None``
        """
        return self.open(ip_addr='tunnel:' + str(serial_no) + ':' + str(port))