Date: Sat, 30 Mar 2002 13:58:34 -0500 From: Steve Ames <steve@virtual-voodoo.com> To: Leo Bicknell <bicknell@ufp.org> Cc: Paul Halliday <dp@penix.org>, hackers@FreeBSD.ORG Subject: Re: GPS time. Message-ID: <20020330185834.GB77994@virtual-voodoo.com> In-Reply-To: <20020330142859.GA19243@ussenterprise.ufp.org> References: <Pine.LNX.4.43L0.0203291757560.4473-100000@saruman.xwin.net> <20020330142859.GA19243@ussenterprise.ufp.org>
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http://www.gpsclock.com/ is $380US and does PPS pulses accurate to plus or minus 1 microsecond of UTC. On Sat, Mar 30, 2002 at 09:28:59AM -0500, Leo Bicknell wrote: > In a message written on Fri, Mar 29, 2002 at 06:04:11PM -0600, Paul Halliday wrote: > > I just connected my gps (garmin gps III plus) to my serial port > > and realized that simply cat'ing cua0 displays date/time/position of the > > unit. (neato). Anyway, how accurate would it be to use the time from this > > output for ntp as opposed to my current setup using ntp servers. > > Your NTP servers are better. > > I tested a III Plus, and without a 1 PPS source (which that model > doesn't provide) it's accurate to about 100ms, give or take. Since > real NTP servers are < 1ms, they really aren't that good. It's > not that the time isn't accurate, it's that they were not designed > to communicate with that accuracy to an external device. > > If you NTP off the Internet, and want a local backup clock it might > be an acceptable solution. However clocks that can achieve < 1ms > accuracy can be had for < $1000, so if you really care you should > get one of those. > > You might want to do some searches for NTP in google. > > -- > Leo Bicknell - bicknell@ufp.org - CCIE 3440 > PGP keys at http://www.ufp.org/~bicknell/ > Read TMBG List - tmbg-list-request@tmbg.org, www.tmbg.org > > To Unsubscribe: send mail to majordomo@FreeBSD.org > with "unsubscribe freebsd-hackers" in the body of the message To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-hackers" in the body of the message
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