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Content preview: Ok so, it won't be problematic in a network in which all nodes
are TelosB... Thank you very much for your explanations. Jonathan
-----Message
d'origine----- De : Jan Hauer [mailto:[email protected]] Envoyé : mercredi
3 février 2010 14:27 À : Jonathan ROY Cc :
[email protected]
Objet : Re: [Tinyos-help] About 802.15.4 on TelosB [...]
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--- Begin Message ---
Ok so, it won't be problematic in a network in which all nodes are TelosB...
Thank you very much for your explanations.
Jonathan
-----Message d'origine-----
De : Jan Hauer [mailto:[email protected]]
Envoyé : mercredi 3 février 2010 14:27
À : Jonathan ROY
Cc : [email protected]
Objet : Re: [Tinyos-help] About 802.15.4 on TelosB
> Hi, I'm a new TinyOS user and I would like to know more about
> the 802.15.4 implementation on TelosB. This platform lacks a hardware
clock
> with sufficient precision/accuracy, but what problems does it imply
concretely
> ? I actually have to use it for evaluating the performance of 802.15.4,
will
> it be possible using TelosB ? [...]
The IEEE 802.15.4 requires a clock with symbol granularity (16us in
2.4 GHz band), i.e. 62.500 Hz. The clock is needed, for example, to
calculate beacon periods or backoffs after a CCA failure. On telosb
there are two clock sources: the external 32.768 Hz quartz and the
MCU-internal DCO. Unfortunately the quartz has the wrong precision and
the DCO doesn't have enough accuracy (+-40 ppm is required).
What the current implementation (tos/lib/mac/tkn154) does is treat one
tick of the quartz as two symbols, which introduces a small error. One
consequence is that when you test interoperability with a 15.4 stack
that has standard-compliant timing you'll get a SYNC_LOSS
(beacon-enabled mode), because the beacon intervals don't match.
Jan
On Wed, Feb 3, 2010 at 12:55 PM, Jonathan ROY <[email protected]>
wrote:
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> Content preview: Hi, I'm a new TinyOS user and I would like to know more
about
> the 802.15.4 implementation on TelosB. This platform lacks a hardware
clock
> with sufficient precision/accuracy, but what problems does it imply
concretely
> ? I actually have to use it for evaluating the performance of 802.15.4,
will
> it be possible using TelosB ? [...]
>
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