On Tue, 30 Sep 2008, Lawrence Stewart wrote: > On Sep 30, 2008, at 12:07 PM, Lux, James P wrote: > > On 9/30/08 8:37 AM, "Robert G. Brown" <[EMAIL PROTECTED]> wrote: > > The grottiest grungy GPS receiver can probably do 100ns on its 1pps > > tick, > > and most are in the 20ns range. There ARE receivers that have > > systematic > > errors (i.e. Some sort of sawtooth in the error) and, of course, > > there are > > countless schemes to compensate in one way or another. > So someone with some grad students and soldering irons should hook up > the 1 pps > output of a GPS to, say, the carrier detect pin on the unused RS232 > ports of all their > nodes, and write some software...
Note that you need a "component" GPS receiver, hooked up with a bunch of wires. The 1 PPS output isn't available from your typical packaged handheld receiver. Those output serial NMEA lines that might be a full second out of date. And once you think about dealing with a 1 PPS signal, you find that you don't even need a GPS. Just a pulse generator. And you can do some other clever things. Or just skip ahead and read about Purdue PAPERS -- figure out why it was very appealing but failed. Meanwhile, I'll try to find out where I can plug a serial cable into a modern server... -- Donald Becker [EMAIL PROTECTED] Penguin Computing / Scyld Software www.penguincomputing.com www.scyld.com Annapolis MD and San Francisco CA _______________________________________________ Beowulf mailing list, [email protected] To change your subscription (digest mode or unsubscribe) visit http://www.beowulf.org/mailman/listinfo/beowulf
