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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def start(self):
 """Initiate fetching of the TOC."""

        self._useV2 = self.cf.platform.get_protocol_version() >= 4

        logger.debug('[%d]: Using V2 protocol: %d', self.port, self._useV2)

        logger.debug('[%d]: Start fetching...', self.port)
        # Register callback in this class for the port
        self.cf.add_port_callback(self.port, self._new_packet_cb)

        # Request the TOC CRC
        self.state = GET_TOC_INFO
        pk = CRTPPacket()
        pk.set_header(self.port, TOC_CHANNEL)
        if self._useV2:
            pk.data = (CMD_TOC_INFO_V2,)
            self.cf.send_packet(pk, expected_reply=(CMD_TOC_INFO_V2,))
        else:
            pk.data = (CMD_TOC_INFO,)
            self.cf.send_packet(pk, expected_reply=(CMD_TOC_INFO,))