Retrives the number of bytes in the SWO buffer.

        Args:
          self (JLink): the ``JLink`` instance

        Returns:
          Number of bytes in the SWO buffer.

        Raises:
          JLinkException: on error

def swo_num_bytes(self):
        """Retrives the number of bytes in the SWO buffer.

        Args:
          self (JLink): the ``JLink`` instance

        Returns:
          Number of bytes in the SWO buffer.

        Raises:
          JLinkException: on error
        """
        res = self._dll.JLINKARM_SWO_Control(enums.JLinkSWOCommands.GET_NUM_BYTES,
                                             0)
        if res < 0:
            raise errors.JLinkException(res)

        return res