[Tinyos-devel] RE: [Tinyos-help] Bug in CC2420 timestamp

Miklos Maroti mmaroti at math.u-szeged.hu
Tue Oct 30 08:29:01 PDT 2007


Hi David,

The problem is not that it overflows, but it contains an inccorect
value. In certain situations there are more packets in the RXFIFO and
we do not know how to pair up the timestamps made for the SFD and the
data packets. This is especially problematic if for some reason some
of those packets get lost or not even get into the RXFIFO.

We should start a discussion on the Timestamping interface. I think it
should be allowed for the radio stack to say that it could not
properly timestamp the packet (just a flag) and the time synch apps
should check for that flag.

Miklos

On 10/30/07, David Moss <dmm at rincon.com> wrote:
> I haven't done much work with the timestamps in the CC2420 apart from
> Jonathan's original implementation, nor have I used it enough to have
> experienced any type of erratic behavior.  Is the issue here that the 16-bit
> timestamp rolls over to 0 periodically?  Would a 32-bit timestamp be better?
>
> -David
>
>
> -----Original Message-----
> From: tinyos-help-bounces at Millennium.Berkeley.EDU
> [mailto:tinyos-help-bounces at Millennium.Berkeley.EDU] On Behalf Of Federico
> Fiorentin
> Sent: Tuesday, October 30, 2007 6:39 AM
> To: tinyos-help at Millennium.Berkeley.EDU
> Subject: [Tinyos-help] Bug in CC2420 timestamp
>
> I'm working on time synchronization with tmote sky motes and TinyOS2.
>
> I'm using a poller that sends a PollPacket every X milliseconds and a
> set of clients that timestamp the arrival time of the PollPacket.
> I found that the 16 timestamp in the time field of the Metadata are
> somethimes incorrect ( CC2420Packet.getMetaData(msg)->time ).
>
> This affects the 1% of the TimeStamps per mote.
> I compared the value "timestamp(n) - timestamp(n-1)" of two different motes.
>
> Is there any patch or a way to fix it?
>
> I appreciate any advice
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