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

[David Moss]

Ted -

Thanks for passing along your experiences and recommendations on timestamps,
these comments are very helpful.  I'm forwarding this along to -devel for
further discussion,

-David


-----Original Message-----
From: Ted Herman [mailto:ted-herman at uiowa.edu] 
Sent: Friday, November 02, 2007 7:40 AM
To: David Moss
Subject: Re: [Tinyos-help] Bug in CC2420 timestamp

David,

I vote no in having a 32-bit timestamp for the metadata. 

I have not experienced any erratic behavior (so far).

I implemented a T2 tsync protocol that I'll be checking into contrib 
pretty soon.  The right way to do this IMO is to generate the timestamps 
within RadioTimeStamping, at whatever <x,y> you think appropriate (in my 
case, I used both 32KHz and Microsec at 32 bits;  the latter is better 
on the receive side for msp430 when the queuing delay is <6.2msec, but 
for atmega, microsec is always better) -- in 
RadioTimeStamping.receivedSFD save the generated timestamps in some 
static location.  The use of the uint16_t time parameter is mainly as a 
key fetched from metadata, later during receive processing, to associate 
the message with the previously stored timestamps.  The documentation is 
pretty clear that RadioTimeStamping events are tentative.  As for 
RadioTimeStamping.transmittedSFD, that's a bit trickier because you need 
to use CC2420Transmit.modify. 

Ted.


David Moss 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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