From owner-freebsd-current Thu Dec 16 12:35:29 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 04C5C14D08 for ; Thu, 16 Dec 1999 12:35:27 -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 NAA08201; Thu, 16 Dec 1999 13:35:24 -0700 (MST) (envelope-from nate@rocky.mt.sri.com) Received: by mt.sri.com (SMI-8.6/SMI-SVR4) id NAA20788; Thu, 16 Dec 1999 13:35:23 -0700 Date: Thu, 16 Dec 1999 13:35:23 -0700 Message-Id: <199912162035.NAA20788@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: <199912162032.NAA73759@harmony.village.org> References: <199912161810.LAA19919@mt.sri.com> <16818.945366687@critter.freebsd.dk> <199912162032.NAA73759@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. > The clock > doesn't want to sync more closely than that, likely due to the large > jitter in the 8254 timing device, so the atomic clock is a bit of a > waste for this part of our application (there are others it is needed > for). With a pentium class machine and w/o the atomic clock > "backing", I'd say you could easily get into the sub-micro second > range. I've got a 486, although running the antenna to an outside window might get exciting. :) Nate To Unsubscribe: send mail to majordomo@FreeBSD.org with "unsubscribe freebsd-current" in the body of the message