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

[Omprakash Gnawali]

Don't most users of timestamp end up implementing the overflow check
on their own? If that is the case, does it make sense to make it a
32-bit timestamp?

- om_p

> 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
> > _______________________________________________
> > Tinyos-help mailing list
> > Tinyos-help at Millennium.Berkeley.EDU
> > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
> >
> >
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> >   
> 
> 
> 
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