<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def start(self):
 """Start the logging for this entry"""

        if (self.cf.link is not None):
            if (self._added is False):
                self.create()
                logger.debug('First time block is started, add block')
            else:
                logger.debug('Block already registered, starting logging'
                             ' for id=%d', self.id)
                pk = CRTPPacket()
                pk.set_header(5, CHAN_SETTINGS)
                pk.data = (CMD_START_LOGGING, self.id, self.period)
                self.cf.send_packet(pk, expected_reply=(
                    CMD_START_LOGGING, self.id))