[ntp:questions] PPS problem

David Lord snews at lordynet.org
Wed Apr 2 10:09:01 UTC 2014


Simchaev Arthur-BAS071 wrote:
> Hi .
> Could you please help me with the following problem ?
> Our board supports PPS & NTP . I connect & define the Garmin GPS(GPS16x-HVS)  as the NMEA reference clock . Unfortunately  when I add the atom reference clock to ntp in order to receive pps , after sometime NMEA & ATOM(pps) clocks marked as falsetick servers . I see that it can related to the jitter and can be fixed by setserial low_latency . But out UART doesn't support this flag .
> Therefore could you please explain how I can fix servers   falsetick problem witout use setserial . Maybe the problem related to number of the servers (I use only  only 2 stratum 0 servers which take the data from the same GPS device )
> Our configuration is following :
> Ntp configuration (ntpd 4.2.6p5) :
> server 127.127.1.0 #lo server
> fudge 127.127.1.0 stratum 7
> 
> restrict 127.127.1.0 noquery nomodify notrap
> server 127.127.20.0 minpoll 4 maxpoll 4 iburst #NMEA Server
> server 127.127.22.0 prefer
> fudge 127.127.22.0 flag3 1 refid PPS

I currently use a "Sure" gps, ntp-dev-4.2.7p433 on NetBSD-6

I have a few significant differences in my ntp.conf

#################
tos orphan 10
tos mindist 0.4  # allows pps to kick in
     ^^^^^^^^^^^
server 127.127.20.2 mode 18
fudge  127.127.20.2 stratum 7 time2 0.407 flag1 0 refid GPSb
server 127.127.22.2 minpoll 4 maxpoll 4
server 127.127.22.2 flag2 0 flag3 1 refid PPSb
server -4 <ntp0.mydomain>
server -4 <ntp1.myisp> minpoll 8 maxpoll 10 iburst prefer
##################

If not using extra server use 127.127.20.0 as prefer peer.


David



> 
> ntpq -p
>      remote           refid      st t when poll reach   delay   offset  jitter
> ==============================================================================
> *LOCAL(0)        .LOCL.           7 l    5   64  377    0.000    0.000   0.031
> xGPS_NMEA(0)     .GPS.            0 l    4   16  377    0.000  -63.203   5.256
> xPPS(0)          .PPS.            0 l    3   64  377    0.000  -347.47   7.428
> root at am335x-evm:/dev# ntpdc
> ntpdc> kerninfo
> pll offset:           0 s
> pll frequency:        0.000 ppm
> maximum error:        0.013456 s
> estimated error:      1e-05 s
> status:               2007  pll ppsfreq ppstime nano
> pll time constant:    6
> precision:            1e-09 s
> frequency tolerance:  500 ppm
> 
> 
> root at am335x-evm:/dev# ntptime
> ntp_gettime() returns code 0 (OK)
>   time d6dd71e6.aaf4cf0c  Wed, Mar 26 2014 15:33:58.667, (.667798707),
>   maximum error 23956 us, estimated error 10 us, TAI offset 0
> ntp_adjtime() returns code 0 (OK)
>   modes 0x0 (),
>   offset 0.000 us, frequency 0.000 ppm, interval 1 s,
>   maximum error 23956 us, estimated error 10 us,
>   status 0x2007 (PLL,PPSFREQ,PPSTIME,NANO),
>   time constant 6, precision 0.001 us, tolerance 500 ppm,
> 
> Regards
> Arthur



More information about the questions mailing list