code: def _hm_form_message_crc(
              self,
              thermostat_id,
              protocol,
              source,
              function,
              start,
              payload
      ):
          
          data = self._hm_form_message(
              thermostat_id, protocol, source, function, start, payload)
          crc = CRC16()
          data = data + crc.run(data)
          return data
docs: Forms a message payload, including CRC