If the time is a free running counter of a 32khz clock won't it overflow since its just a 16bit counter ?
-Avinash
On 7/20/06, Philip Levis
<[EMAIL PROTECTED]> wrote:
On Jul 20, 2006, at 2:25 PM, Avinash Sridharan wrote:
> Hi All,
> I had a question on the timestamping of the packets when the 2.x
> CSMA transmits a packet in the CC2420 stack. When going through the
> code for CC2420CsmaTransmitP.nc, I realised that when the
> CaptureSFD event is called and the state is set to S_SFD the time
> retrieved in this captured event is set into the sent packet. Now
> before sending out the packet a call is made to
> TimeStamp.transmittedSFD with the time of the CaptureSFD event. Now
> the TimeStamp.transmittedSFD code is empty implying that whatever
> was the CaptureSFD event time is actually set on the packet itself.
>
> The time in the CaptureSFD event is a 16 bit value so I am
> assuming it cannot be capturing the 32Khz clock of the MSP430 timer
> (I am using tmotes), so what does this value actually represent ?
> Does it represent the time from the point the transmit request was
> made in which case the timestamping code should add this time to
> the current time (obtained from the local clock) and put in the
> packet metadata?
Jonathan, please correct me if I'm wrong...
The SFD is when the radio actually sends the packet. The time is the
free-running counter of the 32khz clock. I believe the code is empty
because the packet metadata and their mechanisms haven't been nailed
down yet.
Phil
--
Phd Dept. of Electrical Engineering
University of Southern California
http://www-scf.usc.edu/~asridhar
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