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
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