code: def swo_num_bytes(self):
          
          res = self._dll.JLINKARM_SWO_Control(enums.JLinkSWOCommands.GET_NUM_BYTES,
                                               0)
          if res < 0:
              raise errors.JLinkException(res)
  
          return res
docs: 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