Re: Linux system time with NTP/Chrony but no PPS

[Mike Tubby]

    Hi David,
    
    Perhaps I wasn't quite clear enough in my previous post... but
    firstly some background - I run two NTP Stratum 0 clocks over at:
    
        ntp0.thorcom.net
        ntp1.thorcom.net
    
    which are in the UK and also run many clocks on Emergency Services
    customer sites.
    
    We use to use Trimble GPS and the 'parse' driver 127.128.8.0 in
    Trimble TSIP mode:
    
      # Local Trimble TSIP Reference Clock
      server 127.127.8.0 mode 10
    
    (which incidently I had to debug and fix because it was originally
    Big Endian only and written for Sun Workstations or some such
    similar and was buggy on Intel).
    
    We switched to using GPSD several years ago. My Trimble GPS
    receivers have PPS on the RS232 DCD pin and this was a good fit with
    GPSD as it "just works"(tm) for our Reference Clocks. So for our big
    systems we have Trimble GPS with PPS, GPSD with PPS, NTPD and NTPD
    syncs with SHM(1) refid".PPS."
    
    This is our current setup on our Reference Clocks:
    
    ###
      # GPSD reference (using Trimble) and PPS
      ###
      
      # GPS Serial data reference (NTP0)
      server 127.127.28.0 minpoll 4 maxpoll 4
      fudge 127.127.28.0 time1 0.0 flag1 1 refid GPS
      
      # GPS PPS reference (NTP1)
      server 127.127.28.1 minpoll 4 maxpoll 4 prefer
      fudge 127.127.28.1 flag1 1 refid PPS
      
      
      ###
      # Other clocks
      ###
      
      # National Physica Lab (UK)
      server ntp1.npl.co.uk iburst
      server ntp2.npl.co.uk iburst
      
      # Joint Academic Network (UK)
      server ntp1.ja.net iburst
      server ntp2.ja.net iburst
      
      # Manchaester University
      server ntp2d.mcc.ac.uk iburst
      
      # Cambridge University
      #server ntp0.csx.cam.ac.uk iburst
      server ntp1.csx.cam.ac.uk iburst
      server ntp2.csx.cam.ac.uk iburst
      
      # Stathclye University
      server ntp.cis.strath.ac.uk iburst
      
      # Zen Internet - these appear be be un-contactable
      #server ntp0.zen.co.uk
      #server ntp1.zen.co.uk
      
      # US Navy - No longer work - Access controls?
      #server tick.usno.navy.mil iburst
      #server tick.usno.navy.mil iburst
      
      # Google
      server time.google.com iburst
    
    and gives us results like:
    
    ntpq> peers
           remote           refid      st t when poll reach   delay  
      offset  jitter
==============================================================================
      xSHM(0)          .GPS.            0 l    6   16  377    0.000 
      -554.50  12.013
      *SHM(1)          .PPS.            0 l   14   16  377    0.000  
      +0.004   0.017
      +ns1.thorcom.net .PPS.            1 u   27   64  377    0.140  
      -0.050   0.020
      #2a02:8010:7010: 141.32.131.246   2 u   27   64  377   29.550  
      -1.730   0.296
      -ntpsvr1.npl.co. 139.143.45.169   2 u   33   64  377    9.773  
      -0.495   0.024
      -ntpsvr2.npl.co. 139.143.45.169   2 u   37   64  377   10.442  
      -0.606   0.038
      -ntp1.ja.net     .MRS.            1 u   31   64  377   16.028  
      -0.943   0.043
      -ntp2.ja.net     195.66.241.3     2 u   33   64  377   14.974  
      -0.390   0.020
      #swale.mc.man.ac 193.62.22.66     2 u    7   64  377   15.381  
      -0.174   0.206
      +please-update-c 197.205.52.7     2 u   12   64  377   13.442  
      -0.814   0.016
      -ntp0.cis.strath 130.149.17.21    2 u   48   64  377   18.458  
      -1.076   0.034
      -time2.google.co .GOOG.           1 u   22   64  377   14.917  
      -1.086   0.106
      -time-d-g.nist.g .NIST.           1 u   36   64  357   82.162  
      -1.143   0.059
      #time-d-wwv.nist .NIST.           1 u  158   64   64  123.483  
      -1.748 209.925
      ntpq>
    
    
    However that is all well and good, but our new requirement is
    different:

• mobile device running Yocto Dunfell on an NXP iMX6 @ 1000MHz
  
• internet over 4G (could could be unreliable)
• uBlox MAX-M8W connected via serial but without PPS
• GPSD 3.24
  
• NTPD or Chrony - to be decided

    I have never used GPSD without PPS.  The documentation over at:
    
        https://gpsd.gitlab.io/gpsd/gpsd-time-service-howto.html
    
    implies that PPS is part of the solution and we don't have PPS on
    this mobile platform.
    
    So I'm looking to confirm that I can use:
    
        uBlox MAX-M8W (no PPS) -> GPSD (SHM0, no PPS on SHM1) ->
    NTPD or Chrony
    
    initial tests did not work as expected and Chrony responded with all
    zeros rather than working "out of the box", but we're changing
    multiple things on an embedded system under Yocto - which is hard
    work - hence the request for hints or config snippets.
    
    
    Regards
    
    
    Mike

On 08/09/2022 11:52, David Taylor wrote:

> On
>       08/09/2022 11:18, Mike Tubby wrote:
>       
> > Does anyone have hints or a configuration
> >         snippet for Chrony or NTP that
> >         
> >         will work with GPSD without PPS?
> >         
> >         
> >         Regards
> >         
> >         Mike
> >         
> >       
>       
>       Mike,
>       
>       
>       Standard NTP works without a PPS feed, but with limited accuracy,
>       of course.
>       
>       What accuracy do you need?  A very minimum configuration file for
>       NTP might be
>       
>       (assuming Linux):
>       
>       
>       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       
>       # /etc/ntp.conf, configuration for ntpd; see ntp.conf(5) for help
>       
>       
>       # Keep a note of drift across restarts
>       
>       driftfile /var/lib/ntp/ntp.drift
>       
>       
>       # WAN servers
>       
>       pool  uk.pool.ntp.org  maxpoll 7 iburst  prefer
>       
>       pool  de.pool.ntp.org  maxpoll 7 iburst  prefer
>       
>       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>       
>       
>       where the time comes from the best of UK and DE pool servers over
>       the Internet.
>       
>        NTP does not need GPSD to work, nor does GPSD need NTP.
>       
>       
>       Sorry, but I don't use Chrony.
>       
>       
>       Cheers,
>       
>       David
>       
>       --
>       
>       SatSignal Software - Quality software for you
>       
>       Web: https://www.satsignal.eu
>       
>       Email: david-taylor@blueyonder.co.uk
>       
>       Twitter: @gm8arv
>       
>       
>       
>