Although I don't have much advice on clock drift, the CC2420 low power listening transmitter (micaz / tmote) should transmit a little longer than the receive check period, ensuring overlap.
In the case of the CC2420, the 5 ms is approximately how long the radio is in receive mode. The radio actually kicks on for a little longer than that because the crystal oscillator powers up - this is not included in the 5 ms measurement. 5 ms is much less than the amount of time it takes to receive a packet (especially with CSMA) because it's only detecting channel energy. Once it sees energy on the channel, it stays awake longer to receive the packet. The CC1000 radio (mica2) previously did a preamble byte check, which is much more complex than the newer implementations (BMAC) that sense channel energy. In the case of the CC1000 radio, the receive check is much less than 5 ms. -David -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Murray, Ben Sent: Wednesday, August 22, 2007 2:28 AM To: tinyos-help@Millennium.Berkeley.EDU Subject: [Tinyos-help] low power listening - actual listening time? When using low power listening, as discussed in the duty cycle help thread, I understand that the ON time is approx 5 ms. does anyone know approximately how long the radio is actually receiving during this period? I assume that some of it is due to start up time and that the receiver must be enabled for a certain length of time in order to detect a signal. The main reason I ask is because I am trying to work out just how much of a problem clock drift might be. I have read in a paper that the clock drift of a mica2 is approx 40 µs per second which amounts to 2.4 ms per minute. Is there a commonly used rule of thumb perhaps for estimating what the extra amount of time a transmitter might have to be active prior to another Motes estimated low power listening wakeup time. For example, if receive Mote is known to be on a one minute sleep period and the transmit node knows when this receive Mote was last awake, is it normal to begin transmission about 2.4 ms before you think receive Mote might wake up? **************************************************************************** *** Please consider the environment before printing this email. **************************************************************************** *** This email and any files transmitted with it are intended solely for the use of the individual or entity to whom they are addressed and may not be divulged to any third party without the express permission of the originator. Any views expressed in this message are those of the individual sender, except where the sender specifically states them to be the views of Thales Research & Technology (UK) Limited. **************************************************************************** *** _______________________________________________ Tinyos-help mailing list Tinyos-help@Millennium.Berkeley.EDU https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help _______________________________________________ Tinyos-help mailing list Tinyos-help@Millennium.Berkeley.EDU https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
