From owner-freebsd-current Thu Dec 16 12:42: 0 1999 Delivered-To: freebsd-current@freebsd.org Received: from rover.village.org (rover.village.org [204.144.255.49]) by hub.freebsd.org (Postfix) with ESMTP id 5A07E15662 for ; Thu, 16 Dec 1999 12:41:55 -0800 (PST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (harmony.village.org [10.0.0.6]) by rover.village.org (8.9.3/8.9.3) with ESMTP id NAA92614; Thu, 16 Dec 1999 13:41:54 -0700 (MST) (envelope-from imp@harmony.village.org) Received: from harmony.village.org (localhost.village.org [127.0.0.1]) by harmony.village.org (8.9.3/8.8.3) with ESMTP id NAA73896; Thu, 16 Dec 1999 13:41:53 -0700 (MST) Message-Id: <199912162041.NAA73896@harmony.village.org> To: nate@mt.sri.com (Nate Williams) Subject: Re: HEADSUP: ntp4 to replace xntpd Cc: "FreeBSD Current Users' list" In-reply-to: Your message of "Thu, 16 Dec 1999 13:35:23 MST." <199912162035.NAA20788@mt.sri.com> References: <199912162035.NAA20788@mt.sri.com> <199912161810.LAA19919@mt.sri.com> <16818.945366687@critter.freebsd.dk> <199912162032.NAA73759@harmony.village.org> Date: Thu, 16 Dec 1999 13:41:53 -0700 From: Warner Losh Sender: owner-freebsd-current@FreeBSD.ORG Precedence: bulk X-Loop: FreeBSD.ORG In message <199912162035.NAA20788@mt.sri.com> Nate Williams writes: : > : 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. Don't know a thing about the Garmin 12XL to know for sure about how it operates. Warner To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message