[ntp:questions] Re: Garmin gps18: The best DIY gps refclock?

Roman Mäder newsXXF.10.rmaeder at spamgourmet.com
Mon Nov 28 13:17:19 UTC 2005


Eugen COCA wrote:

> Any indication about connecting the PPS signal and setting up the ntpd
> service to work with ?
> 
> Thank you !
> 
> P.S. I think the 1 us jitter is true only if using the PPS signal.

I did configure the PPS device in addition to the NMEA refclock,
but it does not give me any additional accuracy.
this "ntpq -p" output is typical:

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
+GPS_NMEA(0)     .GPS.            0 l   25   64  377    0.000   -0.036   0.020
oPPS(0)          .PPS.            0 l   43   64  377    0.000   -0.046   0.030
...

configured as:

server 127.127.20.0 mode 2 prefer
server 127.127.22.0
fudge 127.127.22.1 flag3 1

I am not sure about the PPS kernel stuff. ntptime gives me

ntp_gettime() returns code 0 (OK)
  time c735804b.b2cb2000  Mon, Nov 28 2005 14:10:35.698, (.698412),
  maximum error 28509 us, estimated error 16 us
ntp_adjtime() returns code 0 (OK)
  modes 0x0 (),
  offset 5.000 us, frequency 6.200 ppm, interval 256 s,
  maximum error 28509 us, estimated error 16 us,
  status 0x107 (PLL,PPSFREQ,PPSTIME,PPSSIGNAL),
  time constant 2, precision 1.000 us, tolerance 512 ppm,
  pps frequency 0.000 ppm, stability 0.000 ppm, jitter 2.000 us,
  intervals 4299, jitter exceeded 12, stability exceeded 12, errors 67.

is this really the "true" PPS, or is there more to it?
This is ntp 4.2.0 on Solaris 8, UltraSPARC

Roman Maeder




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