[ntp:questions] PPS signal from Garmin GPS 18x LVC

Adrian P mailing-lists at pascalau.ro
Sun Dec 29 15:18:37 UTC 2013


Thank you very much David!

So "o" means PPS is used... In my case, I only have "*" in front of
the driver IP.... So I suppose NTP is not using the PPS signal... hmm,
wondering why. This is my output:

server 127.127.20.0 mode 1 minpoll 4 maxpoll 4 prefer
fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 refid PPS

root at debian:~# ntpq -crv -pn
associd=0 status=0415 leap_none, sync_uhf_radio, 1 event, clock_sync,
version="ntpd 4.2.6p5 at 1.2349-o Sat May 12 09:07:18 UTC 2012 (1)",
processor="i686", system="Linux/3.2.0-4-686-pae", leap=00, stratum=1,
precision=-19, rootdelay=0.000, rootdisp=39.519, refid=PPS,
reftime=d66ab9bb.59e07233  Sun, Dec 29 2013 17:09:47.351,
clock=d66ab9ca.45e6469f  Sun, Dec 29 2013 17:10:02.273, peer=52263, tc=4,
mintc=3, offset=14.437, frequency=50.557, sys_jitter=23.063,
clk_jitter=19.669, clk_wander=5.553
     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
*127.127.20.0    .PPS.            0 l   15   16  377    0.000   14.437  23.063
root at debian:~#

This is a Debian linux that I am using right now , and ppswatch is
telling me that PPS signal is present:

root at debian:~# ppswatch /dev/pps0
trying PPS source "/dev/pps0"
found PPS source "/dev/pps0"
timestamp: 1388329896, sequence: 26670, offset:  499040272
timestamp: 1388329897, sequence: 26671, offset:  499085711
timestamp: 1388329897, sequence: 26671, offset:  499085711
timestamp: 1388329898, sequence: 26672, offset:  499128144
timestamp: 1388329898, sequence: 26672, offset:  499128144
timestamp: 1388329899, sequence: 26673, offset:  499221618
^C

Total number of PPS signals: 6
Maximum divergence: 499221618
root at debian:~#

I have also define all relevant device files that 127.127.20.0 driver requires:

root at debian:~# ls -la /dev/ttyS0 /dev/gps0 /dev/pps0 /dev/gpspps0
lrwxrwxrwx 1 root root          5 Dec 29 09:46 /dev/gps0 -> ttyS0
lrwxrwxrwx 1 root root          4 Dec 29 09:46 /dev/gpspps0 -> pps0
crw------- 1 root root    252,  0 Dec 29 09:46 /dev/pps0
crw-rw---T 1 root dialout   4, 64 Dec 29 17:13 /dev/ttyS0
root at debian:~#

The PPS line discipline is attached as well:

root at debian:~# ps -ef | grep ldattach
root       493     1  0 09:46 ?        00:00:00 /usr/sbin/ldattach pps
/dev/ttyS0
root      2157  2069  0 17:15 pts/0    00:00:00 grep ldattach
root at debian:~#

What else should I check?

Many thanks again.


On 29 December 2013 07:59, David Taylor
<david-taylor at blueyonder.co.uk.invalid> wrote:
> On 28/12/2013 20:40, Adrian P wrote:
>>
>> Hi,
>>
>> How do I know that my NTP server is actually using the PPS signal from
>> my Garmin GPS 18x LVC?
>>
>> I have the following NMEA driver configured in /etc/ntp.conf:
>>
>> server 127.127.20.0 mode 1 minpoll 4 maxpoll 4 prefer
>> fudge 127.127.20.0 flag1 1 flag2 0 flag3 1 refid PPS
>>
>> The below output shows me that NTP is using the NMEA GPS clock,
>> however I cannot find anywhere a command that tells me that PPS signal
>> is used as well...
>>
>> root at debian:~# ntpq -c clockvar
>> associd=0 status=00f1 , 15 events, clk_no_reply,
>> device="NMEA GPS Clock",
>>
>> timecode="$GPRMC,202549,A,xxxx.2257,N,xxxxx.2075,E,000.0,195.2,281213,004.8,E,A*1D",
>> poll=13, noreply=36, badformat=0, baddata=0, fudgetime1=0.000, stratum=0,
>> refid=PPS, flags=5
>> root at debian:~#
>>
>> Many thanks,
>> Adrian
>
>
> Adrian,
>
> My understanding is that a "o" as the tally code in the output from ntpq -pn
> indicates PPS sync.  On the two systems here fed from a GPS 18 LVC, with
> some line omitted:
>
> FreeBSD PC Pixie:
>
> server  127.127.20.1    mode 0  minpoll 4 maxpoll 4  prefer
> fudge   127.127.20.1    flag1 1 flag3 1 refid PPS
>
> C:\Users\David>ntpq -crv -pn pixie
> associd=0 status=041f leap_none, sync_uhf_radio, 1 event,
> stale_leapsecond_values,
> version="ntpd 4.2.7p406 at 1.2483 Sat Dec 28 16:28:47 UTC 2013 (1)",
> processor="i386", system="FreeBSD/8.2-RELEASE-p6", leap=00, stratum=1,
> precision=-19, rootdelay=0.000, rootdisp=1.000, refid=PPS,
> reftime=d66a36ed.19d84794  Sun, Dec 29 2013  5:51:41.100,
> clock=d66a36ed.b372d389  Sun, Dec 29 2013  5:51:41.700, peer=32026, tc=4,
> mintc=3, offset=0.007628, frequency=28.823, sys_jitter=0.001907,
> clk_jitter=0.003, clk_wander=0.007, tai=35, leapsec=201207010000,
> expire=201312010000
>      remote           refid      st t when poll reach   delay   offset
> jitter
> ==============================================================================
> o127.127.20.1    .PPS.            0 l    -   16  377    0.000    0.008
> 0.002
> _____________________________________
>
>
> Windows 2000 PC Bacchus:
>
> server  127.127.22.1    minpoll 4               # atom PPS driver
> server  127.127.20.1    minpoll 4       # NMEA serial Garmin GPS 18LVC
> fudge   127.127.20.1    refid NMEA
>
> C:\Users\David>ntpq -crv -pn bacchus
> associd=0 status=01ff leap_none, sync_pps, 15 events,
> stale_leapsecond_values,
> version="ntpd 4.2.7p348 at 1.2891-o Jan 18 13:50:53 (UTC+01:00) 2013  (5)",
> processor="x86", system="Windows", leap=00, stratum=1, precision=-18,
> rootdelay=0.000, rootdisp=1.030, refid=PPS,
> reftime=d66a370c.88361a9d  Sun, Dec 29 2013  5:52:12.532,
> clock=d66a370e.e893b45c  Sun, Dec 29 2013  5:52:14.908, peer=34194, tc=4,
> mintc=3, offset=0.001361, frequency=-5.945, sys_jitter=0.047802,
> clk_jitter=0.054, clk_wander=0.001, tai=35, leapsec=201207010000,
> expire=201212280000, ctr_frequency=4.19
>      remote           refid      st t when poll reach   delay   offset
> jitter
> ==============================================================================
> o127.127.22.1    .PPS.            0 l    3   16  377    0.000    0.001
> 0.048
> +127.127.20.1    .NMEA.           0 l    1   16  377    0.000   -0.051
> 0.041
> _____________________________________
>
> and one fed from a GPS 18x LVC, Windows PC Stamsund:
>
> server  127.127.22.1    minpoll 4       # PPS using serialpps.sys
> fudge   127.127.22.1    refid PPS  flag3 1
> server  127.127.20.1    minpoll 4  mode 33  # 19200bps, NMEA serial port
> fudge   127.127.20.1    refid NMEA
>
> C:\Users\David>ntpq -crv -pn stamsund
> associd=0 status=011f leap_none, sync_pps, 1 event, stale_leapsecond_values,
> version="ntpd 4.2.7p406 at 1.2483-o Dec 28 16:04:29.64 (UTC-00:00) 2013  (1)",
> processor="x86", system="Windows", leap=00, stratum=1, precision=-22,
> rootdelay=0.000, rootdisp=1.225, refid=PPS,
> reftime=d66a375c.3e52fa96  Sun, Dec 29 2013  5:53:32.243,
> clock=d66a376b.d26fb21b  Sun, Dec 29 2013  5:53:47.822, peer=46859, tc=4,
> mintc=3, offset=0.088931, frequency=-6.839, sys_jitter=0.034536,
> clk_jitter=0.026, clk_wander=0.001, tai=35, leapsec=201207010000,
> expire=201312010000
>      remote           refid      st t when poll reach   delay   offset
> jitter
> ==============================================================================
> o127.127.22.1    .PPS.            0 l   15   16  377    0.000    0.089
> 0.035
> +127.127.20.1    .NMEA.           0 l   14   16  377    0.000    0.021
> 0.018
> _____________________________________
>
>
> I hope that helps!
>
> --
> Cheers,
> David
> Web: http://www.satsignal.eu
>
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