[ntp:questions] Using PPS

David Taylor david-taylor at blueyonder.co.uk.invalid
Thu Dec 27 14:37:12 UTC 2012


On 27/12/2012 10:55, Joshua Small wrote:
> Hi,
>
> I built an NTP server with a GPS and PPS as per this guide (exact hardware):
>
> http://open.konspyre.org/blog/2012/10/18/raspberry-pi-time-server/
>
> I got things up and running with the same result as per said guide, before determining that my PPS wasn't wired up correctly.
> I fixed that, and now I'm sure it's wired up - it's now detected in dmesg, and ppstest indicates it's running.
>
> As far as any NTP diagnostic I can find goes however, nothing is any different (it feels like I have less drift, but I didn't keep graphs before), which leads me to the question of "how do I know it's working?".
>
> As per the guide, I run this in ntp.conf:
>
> server 127.127.20.0 mode 17 minpoll 3 iburst true prefer
> fudge 127.127.20.0 flag1 1 time2 0.496
>
> I can definitely see, in ntpq -p, the GPS_NMEA driver being used.
>
> I can see a related thread here:
>
> http://ml.enneenne.com/pipermail/linuxpps/2009-February/002888.html
>
> Specifically, my googling generally pointed me at looking for PPSSIGNAL in the status, however, it seems that a lack of it (as is my case) is "normal" in many circumstances.
>
> Any advice appreciated.
>
> -Josh.

Josh,

My own notes on the Raspberry Pi are here:

   http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#pps

I hope there is some useful diagnostic information there.  You should a 
"o" against the PPS source in the "ntpq -p" output, and a "kern" entry 
in the "ntpq -c rv" output.

Here are the results from my Raspberry Pi:

C:\Users\David>ntpq -c rv 192.168.0.14
associd=0 status=011d leap_none, sync_pps, 1 event, kern,
version="ntpd 4.2.7p329 at 1.2483 Sun Dec  2 09:10:46 UTC 2012 (1)",
processor="armv6l", system="Linux/3.2.27-pps-g965b922-dirty", leap=00,
stratum=1, precision=-19, rootdelay=0.000, rootdisp=1.135, refid=PPS,
reftime=d486da8e.004dd4ef  Thu, Dec 27 2012 14:32:46.001,
clock=d486da97.0dff9b5b  Thu, Dec 27 2012 14:32:55.054, peer=2679, tc=4,
mintc=3, offset=0.001799, frequency=-41.199, sys_jitter=0.002386,
clk_jitter=0.000, clk_wander=0.000

C:\Users\David>ntpq -p 192.168.0.14
      remote           refid      st t when poll reach   delay   offset 
  jitter
==============================================================================
oPPS(0)          .PPS.            0 l    8   16  377    0.000    0.002 
  0.002
*pixie           .PPS.            1 u   14   32  377    0.511   -0.012 
  0.031
+FEENIX          .PPS.            1 u   17   32  377    0.605    0.028 
  0.028
+Stamsund        .PPS.            1 u    6   32  377    0.601   -0.039 
  0.135
  uk.pool.ntp.org .POOL.          16 p    - 1024    0    0.000    0.000 
   0.002
-time.mhd.uk.as4 213.229.82.130   3 u  396 1024  377   24.654   13.474 
  5.664
-dawn.rt.uk.eu.o 193.79.237.14    2 u 1066 1024  377   19.163    2.598 
  3.815
-cadmium.cloudfa 195.66.241.2     2 u  103 1024  377   26.394    2.699 
  3.609
-time.dan.me.uk  82.148.230.254   2 u  787 1024  377   17.598    0.409 
  3.568
-- 
Cheers,
David
Web: http://www.satsignal.eu



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