[Tinyos-help] 802.15.4

Aitor Hernandez aitorhh at kth.se
Thu Nov 18 01:02:11 PST 2010


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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