docs: def __sendCommand(self, cmd):
          """send specific command to reference unit over serial port
  
          Args:
              cmd: OpenThread CLI string
  
          Returns:
              Done: successfully send the command to reference unit and parse it
              Value: successfully retrieve the desired value from reference unit
              Error: some errors occur, indicates by the followed specific error number
          """
          logging.info('%s: sendCommand[%s]', self.port, cmd)
          if self.logThreadStatus == self.logStatus['running']:
              self.logThreadStatus = self.logStatus['pauseReq']
              while self.logThreadStatus != self.logStatus['paused'] and self.logThreadStatus != self.logStatus['stop']:
                  pass
  
          try:
              # command retransmit times
              retry_times = 3
              while retry_times > 0:
                  retry_times -= 1
                  try:
                      self._sendline(cmd)
                      self._expect(cmd)
                  except Exception as e:
                      logging.exception('%s: failed to send command[%s]: %s', self.port, cmd, str(e))
                      if retry_times == 0:
                          raise
                  else:
                      break
  
              line = None
              response = []
              retry_times = 10
              while retry_times > 0:
                  line = self._readline()
                  logging.info('%s: the read line is[%s]', self.port, line)
                  if line:
                      response.append(line)
                      if line == 'Done':
                          break
                  else:
                      retry_times -= 1
                      time.sleep(0.2)
              if line != 'Done':
                  raise Exception('%s: failed to find end of response' % self.port)
              logging.info('%s: send command[%s] done!', self.port, cmd)
              return response
          except Exception, e:
              ModuleHelper.WriteIntoDebugLogger("sendCommand() Error: " + str(e))
              raise