From owner-freebsd-current Thu Dec 16 12:44:15 1999 Delivered-To: freebsd-current@freebsd.org Received: from ns.mt.sri.com (ns.mt.sri.com [206.127.79.91]) by hub.freebsd.org (Postfix) with ESMTP id A6CB115742 for ; Thu, 16 Dec 1999 12:44:10 -0800 (PST) (envelope-from nate@mt.sri.com) Received: from mt.sri.com (rocky.mt.sri.com [206.127.76.100]) by ns.mt.sri.com (8.9.3/8.9.3) with SMTP id NAA08310; Thu, 16 Dec 1999 13:44:00 -0700 (MST) (envelope-from nate@rocky.mt.sri.com) Received: by mt.sri.com (SMI-8.6/SMI-SVR4) id NAA20958; Thu, 16 Dec 1999 13:43:46 -0700 Date: Thu, 16 Dec 1999 13:43:46 -0700 Message-Id: <199912162043.NAA20958@mt.sri.com> From: Nate Williams MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit To: Warner Losh Cc: nate@mt.sri.com (Nate Williams), "FreeBSD Current Users' list" Subject: Re: HEADSUP: ntp4 to replace xntpd In-Reply-To: <199912162041.NAA73896@harmony.village.org> References: <199912162035.NAA20788@mt.sri.com> <199912161810.LAA19919@mt.sri.com> <16818.945366687@critter.freebsd.dk> <199912162032.NAA73759@harmony.village.org> <199912162041.NAA73896@harmony.village.org> X-Mailer: VM 6.34 under 19.16 "Lille" XEmacs Lucid Reply-To: nate@mt.sri.com (Nate Williams) Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG > : > : You may not know the answer to this, but it's worth a shot. Wht kind of > : > : accuracy can we expect using 'cheap' off-the-shelf GPS receivers? > : > > : > We're getting, with ntp4 on a 3.x kernel, about +- 4uSec with a cheap > : > gps receiver + atomic clock on a i486 class machine. > : > : I've got the cheap gps receiver (Garmin 12XL), but what do you mean by > : an 'atomic clock'? Should the GPS receiver's NMEA messages be adequate > : enough to do the job? However, all I need is ms accuracy, so anything > : below 500us is good enough for me. > > We have a cesium clock, which is generally called atomic clock, that > we use for various things in our system. If the GPS gives out a PPS > signal for the NMEA, then you can likely hit 1mS w/o any problems at > all. Cool. I was under the impression that the cheap NMEA signals only gave 2-5sec accuracy given the 2400 baud speed issues. > Don't know a thing about the Garmin 12XL to know for sure about > how it operates. It just a standard 'cheap' GPS. Nate To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message