Inexpensive OEM GPS units? - NTP

This is a discussion on Inexpensive OEM GPS units? - NTP ; On 2007-11-18, Chris Adams wrote: > I've only got one serial port (and it is a console), so I don't have > any other way to connect but USB (also, I'm using a USB to serial > adapter to pull ...

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Thread: Inexpensive OEM GPS units?

  1. Re: Inexpensive OEM GPS units?

    On 2007-11-18, Chris Adams wrote:

    > I've only got one serial port (and it is a console), so I don't have
    > any other way to connect but USB (also, I'm using a USB to serial
    > adapter to pull +5V from the USB port). Everyone keeps saying that USB
    > must be bad, but I was trying to see just how much impact USB has.


    What does ntpq -p show?

    --
    Steve Kostecke
    NTP Public Services Project - http://support.ntp.org/

  2. Re: Inexpensive OEM GPS units?

    Once upon a time, Steve Kostecke said:
    >What does ntpq -p show?


    $ ntpq -p
    remote refid st t when poll reach delay offset jitter
    ================================================== ============================
    -fly.hiwaay.net 192.5.41.40 2 u 2 64 377 16.351 9.846 1.449
    +lashiir.sapros. 74.53.198.146 3 u 36 64 377 48.593 6.778 0.636
    +newton.8086.net 209.51.161.238 2 u 39 64 377 27.075 5.322 0.970
    -ntp.unknowndevi 18.26.4.105 2 u 52 64 377 51.295 -9.173 6.805
    LOCAL(0) .LOCL. 10 l 52 64 377 0.000 0.000 0.002
    xGPS_NMEA(0) .GPS. 0 l 11 64 377 0.000 143.198 56.164
    *SHM(0) .SHM. 0 l 2 16 377 0.000 -0.195 0.541
    $

    The PPS is run via shm_splc2, so the GPS_NMEA is guaranteed to be off
    (but it gets the date/time info). This is using pool servers plus an
    ISP server (across a DSL link from my box).
    --
    Chris Adams
    Systems and Network Administrator - HiWAAY Internet Services
    I don't speak for anybody but myself - that's enough trouble.

  3. Re: Inexpensive OEM GPS units?

    On 2007-11-19, Chris Adams wrote:
    > Once upon a time, Steve Kostecke said:
    >>What does ntpq -p show?

    >
    > $ ntpq -p
    > remote refid st t when poll reach delay offset jitter
    >================================================== =================


    > xGPS_NMEA(0) .GPS. 0 l 11 64 377 0.000 143.198 56.164
    > *SHM(0) .SHM. 0 l 2 16 377 0.000 -0.195 0.541


    Compare your PPS over USB with PPS on a real serial port:

    rackety.udel.edu
    remote refid st t when poll reach delay offset jitter
    ================================================== =================
    +SPECTRACOM(1) .GPS1. 0 l 21 64 377 0.000 0.004 0.004
    oPPS(0) .PPS. 0 l 5 16 377 0.000 0.002 0.004

    The GPS-18LVC connected to a real serial port on my Soekris would show
    jitter of 0.008 and a typical daily peersum (with peer.awk) looked like:

    ident cnt mean rms max delay dist disp
    ================================================== ==========
    127.127.20.0 5235 0.000 0.002 0.014 0.000 0.270 0.248

    --
    Steve Kostecke
    NTP Public Services Project - http://support.ntp.org/

  4. Re: Inexpensive OEM GPS units?

    Chris Adams wrote:
    > Once upon a time, Steve Kostecke said:
    >> What does ntpq -p show?

    >
    > $ ntpq -p
    > remote refid st t when poll reach delay offset jitter
    > ================================================== ============================
    > -fly.hiwaay.net 192.5.41.40 2 u 2 64 377 16.351 9.846 1.449
    > +lashiir.sapros. 74.53.198.146 3 u 36 64 377 48.593 6.778 0.636
    > +newton.8086.net 209.51.161.238 2 u 39 64 377 27.075 5.322 0.970
    > -ntp.unknowndevi 18.26.4.105 2 u 52 64 377 51.295 -9.173 6.805
    > LOCAL(0) .LOCL. 10 l 52 64 377 0.000 0.000 0.002
    > xGPS_NMEA(0) .GPS. 0 l 11 64 377 0.000 143.198 56.164
    > *SHM(0) .SHM. 0 l 2 16 377 0.000 -0.195 0.541
    > $
    >
    > The PPS is run via shm_splc2, so the GPS_NMEA is guaranteed to be off
    > (but it gets the date/time info). This is using pool servers plus an
    > ISP server (across a DSL link from my box).


    I run a Garmin GPS 18 LVC over serial, and get the PPS signal via the shmpps
    (shm_splc2) driver. Here is my 'ntpq -p' and 'ntpq -crv':

    saturn:$ ntpq -p
    remote refid st t when poll reach delay offset jitter
    ================================================== ============================
    *SHM(0) .PPS. 0 l 13 16 377 0.000 0.000 0.001
    -bigben.cac.wash .USNO. 1 u 26 64 377 13.568 -1.107 2.694
    -clepsydra.dec.c .GPS. 1 u 37 64 377 32.296 -1.607 3.923
    -time.sdsc.edu .WWVB. 1 u 4 64 377 41.676 -4.008 2.228
    -clock.sjc.he.ne .CDMA. 1 u 5 64 377 33.254 -1.262 1.950
    +tick.ucla.edu .GPS. 1 u 48 64 377 42.264 -0.820 6.585
    +clock.xmission. .GPS. 1 u 4 64 377 51.862 -0.540 1.430

    saturn:$ ntpq -crv
    assID=0 status=0964 leap_none, sync_telephone, 6 events, event_peer/strat_chg,
    version="ntpd 4.2.4p4@1.1520 Sun Oct 7 00:42:35 UTC 2007 (2)",
    processor="i686", system="Linux/2.6.17-5mdv", leap=00, stratum=1,
    precision=-20, rootdelay=0.000, rootdispersion=0.243, peer=28353,
    refid=PPS, reftime=caebb9b5.a65ccee4 Sun, Nov 18 2007 23:28:53.649,
    poll=4, clock=caebb9b6.5599d760 Sun, Nov 18 2007 23:28:54.334, state=4,
    offset=0.000, frequency=-22.465, jitter=0.001, noise=0.001,
    stability=0.000

    --
    Dennis Hilberg, Jr. timekeeper(at)dennishilberg(dot)com
    NTP Server Information: http://saturn.dennishilberg.com/ntp.php

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