The Moteiv Boomerang code made an attempt at adjusting for skew but was somewhat sadly short in its estimate of how much drift was acceptable. I believe the Xbow XMESH code also adjusts, perhaps even on a message by message basis. I don't know about the other versions of low-power ad-hocking, but the general program is to try to time sync in order to wakeup and exchange messages at regular intervals.
It's not necessarily a centralized thing though. Each node gets messages from it's neighbors with timestamps and compares the differences over time. I don't know if anyone has examined it, but it's a nice example of synchronized oscillators which can have "regular" or "chaotic" behaviors. MS Raffaele Gravina wrote: > Well... i believe it's about time synchronization, isn't it? You need a > "trusted" source of clocking in order to correct your drift. > Am i wrong? > > raf > > 2009/7/17 Eric Decker <[email protected] <mailto:[email protected]>> > > on the telosb it is done once on boot and then not done again. > > in other words it is something you have to figure out how to > provide. Most of the pieces are in the code. > > eric > > > On Fri, Jul 17, 2009 at 4:03 PM, Raffaele Gravina > <[email protected] <mailto:[email protected]>> wrote: > > Which is the easiest way to correct it? Does TinyOS provide with > a specific api/component or is something one would do by himself? > > - Raf > > 2009/7/17 Michael Schippling <[email protected] > <mailto:[email protected]>> > > One would have to look at the specs for the crystal used > but something like .1% (or less) sticks in mind. Whatever > it is, it seems small but actually leads to significant drift > if not frequently corrected. > > MS > > Yi-Tao Wang wrote: > > Hi, > > > > Does anyone know the clock skew I can expect from a tmote > sky? > > > > Thanks, > > > > David > > _______________________________________________ > > Tinyos-help mailing list > > [email protected] > <mailto:[email protected]> > > > > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > _______________________________________________ > Tinyos-help mailing list > [email protected] > <mailto:[email protected]> > > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > <https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help> > > > _______________________________________________ > Tinyos-help mailing list > [email protected] > <mailto:[email protected]> > > https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help > > > > > -- > Eric B. Decker > Senior (over 50 :-) Researcher > Autonomous Systems Lab > Jack Baskin School of Engineering > UCSC > > > > > -- > Raffaele Gravina | Research Engineer > > Wireless Sensor Networks Lab Berkeley > 2000 Hearst Ave, suite 304 > Berkeley, CA 94709 > +1 510 666 0174 ext. 101 _______________________________________________ Tinyos-help mailing list [email protected] https://www.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
