From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-wi0-f175.google.com (mail-wi0-f175.google.com [209.85.212.175]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 3345F2020B8 for ; Tue, 1 May 2012 18:40:37 -0700 (PDT) Received: by wibhn6 with SMTP id hn6so3760438wib.10 for ; Tue, 01 May 2012 18:40:34 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:in-reply-to:references:date:message-id:subject:from:to :cc:content-type:content-transfer-encoding; bh=iFtSfisXPPq18NFrNpFTmc48aFgX6yNgBJe1KVwa4mw=; b=rYD46zEM2i+iuRTByKcGZyNghUALdb6Akmyobzhy+J8u0D2JqQ7Ljs98czVl0fD5Lp JIW8EDWLJ6aKYnvJwHBKsWEFgXTENLnrg+9dJyAGzmkwb7hFpp6JHSh6qau7qcGZ3sT6 iTDx0Q/NrLUk0yWS1NGibo7b5fFHucK9GpmSfJFHKcCKgGXh4aH7uQeHbTAb8BOUcLnP 8z4TILIhBuxl4shM69Ufpm8daqUy0faosASzsMI2uYpbyTyE1cJ8zDssO6xQ5x1b+Bo7 sVOzVk6Ko3/p/Db93h4ZsTGV+LazWaJCcwcvYRP+qIMjM3Dx3iYPqwrwx9QqG9cNgagj sCUw== MIME-Version: 1.0 Received: by 10.216.134.28 with SMTP id r28mr1815641wei.2.1335922834733; Tue, 01 May 2012 18:40:34 -0700 (PDT) Received: by 10.223.112.66 with HTTP; Tue, 1 May 2012 18:40:34 -0700 (PDT) In-Reply-To: <20120501151435.4a6a5373.gem@rellim.com> References: <20120501151435.4a6a5373.gem@rellim.com> Date: Tue, 1 May 2012 18:40:34 -0700 Message-ID: From: Dave Taht To: "Gary E. Miller" Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Cc: thumbgps-devel@lists.bufferbloat.net, gpsd-dev@nongnu.org Subject: Re: [Thumbgps-devel] [gpsd-dev] PPS over USB X-BeenThere: thumbgps-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Wed, 02 May 2012 01:40:37 -0000 I'm a little confused. There are two threads going by today. One is about a sirfIII and the other a ublox 6 I have been assuming they are one and the same, but perhaps I'm confused. Secondly an item that has not been looked into much is the quality of the antennas, or the quality of the clock source when only a single sat is available.... Thirdly, wow.... when can I get one of these puppies to play with? :me looks out his bay window wistfully: On Tue, May 1, 2012 at 3:14 PM, Gary E. Miller wrote: > Yo All! > > As some of you may know, esr has been helping the bufferbloat project > with some gpsd issues. =A0Their goal is to get good time from a USB > connected GPS. > > Esr negotiated with Navisys to special build three units of a ublox 6 > and a pl2303 with PPS conencted to USB. =A0They call them a GR-601 and I > just received the samples. =A0The preliminary results are pretty good if = a > clock stable to about 1 milliSec is your goal. > > A preliminary result from a dual core laptop. > > # ntpq -p > =A0 =A0 remote =A0 =A0 =A0 =A0 =A0 refid =A0 =A0 =A0st t when poll reach = =A0 delay =A0 offset > jitter > =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D= =3D=3D=3D=3D > -backup =A0 =A0 =A0 =A0 =A0.SOC1. =A0 =A0 =A0 =A0 =A0 1 u =A0 45 =A0 64 = =A0377 =A0 =A00.233 -0.006 =A0 0.067 > +fuzzy =A0 =A0 =A0 =A0 =A0 .GPS1. =A0 =A0 =A0 =A0 =A0 1 u =A0 47 =A0 64 = =A0377 =A0 =A00.241 -0.047 =A0 0.071 > +SHM(0) =A0 =A0 =A0 =A0 =A0.GPS. =A0 =A0 =A0 =A0 =A0 =A00 l =A0 10 =A0 16= =A0377 =A0 =A00.000 -2.995 =A0 1.656 > *SHM(1) =A0 =A0 =A0 =A0 =A0.GPS1. =A0 =A0 =A0 =A0 =A0 0 l =A0 =A09 =A0 16= =A0377 =A0 =A00.000 =A00.317 =A0 0.428 > > > backup and fuzzy each have a PPS clock directly connected over serial. > The jitter on backup is about 2 microSec and fuzzy about 0.5 microSec. > And they tend to agree over ntp to about 20 microSec or better. > > All the NTP servers are adjacent to each other and connected over GigE. > The jitter over the GigE seems to be about 100 microSec or better. > > SHM(0) is NMEA time over USB. =A0SHM(1) is PPS time over USB. > > As you can see the NMEA/USB short term jitter is about 2 milliSec and > the PPS/USB time is about 0.5 milliSec jitter. =A0Long term NMEA/USB drif= t > is quite a bit larger, maybe 100 milliSec or more. > > So the jitter of PPS over USB is about 50x worse than PPS over GigE, but > I think for the purposes at hand pretty good. =A0Of course I expect the > results to be worse when run on a single core router. > > The important part of the ntp.conf: > > =A0 =A0# for gpsd > =A0 =A0server 127.127.28.0 minpoll 4 maxpoll 4 > =A0 =A0fudge 127.127.28.0 time1 0.142 =A0refid GPS > > =A0 =A0# for PPS and gpsd > =A0 =A0server 127.127.28.1 prefer =A0minpoll 4 maxpoll 4 > =A0 =A0fudge 127.127.28.1 time1 0.001500 refid GPS1 > > I start the daemons this way: > > =A0 =A0ntpd -p /var/run/ntpd.pid -N -u ntp:ntp -g > =A0 =A0gpsd -n /dev/ttyUSB0 > > Any questions or suggestions? > > RGDS > GARY > -------------------------------------------------------------------------= -- > Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97701 > =A0 =A0 =A0 =A0gem@rellim.com =A0Tel:+1(541)382-8588 --=20 Dave T=E4ht SKYPE: davetaht US Tel: 1-239-829-5608 http://www.bufferbloat.net