[Tinyos-help] 802.15.4

Jan Hauer hauer at tkn.tu-berlin.de
Thu Nov 18 01:46:20 PST 2010


yes - I can reproduce the problem and also believe that it is due to
wrong (beacon) timestamps. will look into it and try to fix it asap.

thanks,
jan

On Thu, Nov 18, 2010 at 10:02 AM, Aitor Hernandez <aitorhh at kth.se> wrote:
> Hi guys,
> I've seen this problem with TKN15.4. It is possible to synchronize N nodes
> with TKN15.4 the problem is that they need to start the app at the same
> time. From my experience I've realized that the problem comes from the
> cc2420_tkn154 (maybe it happens with the default cc2420 implementation as
> well).
> If we have a network with N nodes running and transmitting data between
> them, when we try to add another node we could have this problem. As far as
> we have the radio enabled for reception for a long period (Scan period), the
> cc2420 receives the beacons but data packets as well. Once it detects that
> the received packet is a beacon, it sets the timestamp, but sometimes the
> timestamp is wrong, due to the data packets, and then we lost the next
> beacons.
> Possible solutions:
>
> Check the CC2420ReceiveP.nc and the m_timestamp_queue. I guess that the
> problem should be there. I did some modifications on
> the CC2420ReceiveP.nc to solve this problem, but I haven't test it properly.
> If we lost the synchronization, scan again with MLME_SCAN.request(). It is a
> "fake" solution, because the problem is still there, but for some app it
> will work.
> Start the nodes at the same time. It is not possible in a real deployment.
>
>
> --
> Aitor Hernandez
> KTH | Automatic Control
> Research engineer
> Stockholm
> Phone:  +46 (0)704 26 87 99
>
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