From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-we0-f171.google.com (mail-we0-f171.google.com [74.125.82.171]) (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 B97E02001A2 for ; Tue, 1 May 2012 15:16:59 -0700 (PDT) Received: by werf13 with SMTP id f13so10909wer.16 for ; Tue, 01 May 2012 15:16:57 -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 :content-type; bh=Ar/Q6KBGdDhuYphSyZ0dwjplwQs/outsxz3PZ9IUgBI=; b=LS+AFY+As4/l+6zy4CG1Txtp/QCVEs/p4aLgS19xUfF40XkrAiXdzmh8xN4rcAiVC0 Z2TCNThgH9ZJkQQjyPyfLU7cYeJ4wM7pPeQIOgQqOc36k/cC3qj+eRZXEe1+Ga/vTpLF yVA6vXYq+x2ndm2BxsVVV8xTiV/fi7k8+MlUKbj450NTxJA4R6Bx0DAuPWduJx/NCbQd uSaB0rDM8BpByNZQX6MKWnItL+4EY1JtzeA1x0Jk6y82j26G7t+Xa1erqwFSTUpnZRPl P144Rtrm4fK1N/KD4sE/E+xy5E3I5UZlQtkLFRFFY8cVAUcRCHMbIY/TcN/CWxlzRM08 EX2Q== MIME-Version: 1.0 Received: by 10.180.88.169 with SMTP id bh9mr8492478wib.5.1335910617660; Tue, 01 May 2012 15:16:57 -0700 (PDT) Received: by 10.223.112.66 with HTTP; Tue, 1 May 2012 15:16:57 -0700 (PDT) In-Reply-To: <20120501151435.4a6a5373.gem@rellim.com> References: <20120501151435.4a6a5373.gem@rellim.com> Date: Tue, 1 May 2012 15:16:57 -0700 Message-ID: From: Dave Taht To: thumbgps-devel@lists.bufferbloat.net Content-Type: multipart/mixed; boundary=f46d04182570d13dc604bf00ed62 Subject: [Thumbgps-devel] Fwd: [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: Tue, 01 May 2012 22:17:00 -0000 --f46d04182570d13dc604bf00ed62 Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable ---------- Forwarded message ---------- From: Gary E. Miller Date: Tue, May 1, 2012 at 3:14 PM Subject: [gpsd-dev] PPS over USB To: gpsd-dev@nongnu.org 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 =A0= 377 =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 =A0= 377 =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 drift 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 --f46d04182570d13dc604bf00ed62 Content-Type: application/pgp-signature; name="signature.asc" Content-Disposition: attachment; filename="signature.asc" Content-Transfer-Encoding: base64 X-Attachment-Id: 97549f0205d2e269_0.1 LS0tLS1CRUdJTiBQR1AgU0lHTkFUVVJFLS0tLS0NClZlcnNpb246IEdudVBHIHYyLjAuMTcgKEdO VS9MaW51eCkNCg0KaUVVRUFSRUNBQVlGQWsrZ1lFNEFDZ2tRQm1uUnF6NzFPdk5tTndDZ2hCdUMw WDgwMWJOWEp3eXB0QUgxVVpJbQ0KbE1nQW1JL0MxNExoV0dxdDUyTFBJNzh4c2NLeFN2WT0NCj14 SVRIDQotLS0tLUVORCBQR1AgU0lHTkFUVVJFLS0tLS0NCg== --f46d04182570d13dc604bf00ed62--