[ntp:questions] Trimble Resolution SMT on Ubuntu 12.04

Dave Hart hart at ntp.org
Thu Mar 29 04:56:50 UTC 2012


On Mon, Mar 26, 2012 at 16:06, G <geng_j at yahoo.com> wrote:
> I use Trimble Resolution SMT to sync time for a Ubuntu 12.04 server (kernel 3.2.0).
>
> Trimble send NMEA to /dev/ttyUSB1(9600 8N1) on Ubuntu  server
> PPS signal connect ACK pin on  /dev/parport0 . Ubuntu load Linux-PPS module( PPS_parport clear_wait=0) to create PPS device /dev/pps0
>
> I use verify the /dev/pps0  using rising edge by "ppstest /dev/pps0"
> --------------------------------------------------------------------------------------------
> trying PPS source "/dev/pps0"
> found PPS source "/dev/pps0"
> ok, found 1 source(s), now start fetching data...
> source 0 - assert 1332775909.500413150, sequence: 249302 - clear  0.000000000, sequence: 0
> source 0 - assert 1332775910.500456132, sequence: 249303 - clear  0.000000000, sequence: 0
> source 0 - assert 1332775911.500499213, sequence: 249304 - clear  0.000000000, sequence: 0
> -----------------------------------------------------------------------------------------------
> To verify the NMEA message , I link /dev/ttyUSB1 to /dev/gps1
> -----------------------------------------------------------------------------------------------
> #cat /dev/gps1
> $GPRMC,153343.000,A,4529.904930,N,07343.904831,W,0.241,325,260312,,,A*6F
> $GPGGA,153344.000,4529.905010,N,07343.904879,W,1,3,3.17,12.368,M,-32.087,M,,*5E
> ---------------------------------------------------------------------------------------------------
> I create the /etc/ntp.conf:
> -------------------------------------------------------------------------
> server 127.127.20.1 mode 17 prefer       # NMEA RMC/GGA 9600bps

mode 17 is 16 (9600) plus 1 (select RMC)

> fudge 127.127.20.1 time2 0.01
>
> server 127.127.22.0 minpoll 4 maxpoll 4  # PPS ATOM
> fudge 127.127.22.0 flag2 0 flag3 1
>
> driftfile /var/lib/ntp/ntp.drift
> ------------------------------------------------------------------------------
> after ntpd run 48hours, ntpq -p:
>
>      remote           refid     st t when poll reach   delay   offset  jitter
> ==============================================================================
> xGPS_NMEA(1)     .GPS.            0 l   44   64  377    0.000  -214.54  25.464
> xPPS(0)          .PPS.            0 l   11   16  377    0.000  -174.60   4.981
>
>
> I have no idea why I got this result . what do I miss for config? by the way , I compile ntpd from source , not using ntpd from Ubuntu.

I'm not sure why you're seeing that result.  First, flag3 1 doesn't
appear to be working, in that the offset of the PPS is far away.
Moreover, when  feasible I suggest using NMEA's built-in PPSAPI
support.  You should be able to to remove the PPS refclock and add
flag1 1 to the fudge 127.127.20.1 line, then add a soft link from
/dev/gpspps1 to /dev/pps0.  This eliminates the risk of two clocks
whose confidence intervals don't overlap both being tossed as
falsetickers, as your PPS will be provided via the same refclock.

Good luck,
Dave Hart


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