[ntp:questions] fudge time1 for gps-18x-LVC?

David J Taylor david-taylor at blueyonder.delete-this-bit.and-this-part.co.uk.invalid
Sun Feb 7 09:35:26 UTC 2010


"David Lord" <snews at lordynet.org> wrote in message 
news:7t6oaaFul7U1 at mid.individual.net...
[]
> Now NMEA(0) 92u/6u and PPS(0) 75u/2u, 60 minutes after ntpd restarted.
>
>  Config:
>  pps to lpt0
>  pps to serial dcd
>  lpt0 at ppbus
>  pps0 at ppbus
>  crw-r--r--  1 root    wheel     164,       0 Feb  7 01:47 pps0
>  server 127.127.20.0 mode 1 prefer minpoll 6   maxpoll 8
>  server 127.127.22.0 minpoll 4 maxpoll 6
>
>  7 Feb 01:46:18 ntpd exiting on signal 15
>  7 Feb 01:47:38 clock PPS(0) event 'clk_noreply' (0x01)
>  7 Feb 01:51:58 synchronized to 192.168.59.60, stratum 2
>  7 Feb 01:51:58 kernel time sync status change
>                 0x2001<PLL,NANO,MODE=0x0=PLL,CLK=0x0=A>
>  7 Feb 01:51:59 synchronized to GPS_NMEA(0), stratum 0
>  7 Feb 01:53:09 synchronized to PPS(0), stratum 0
>
>       remote       refid      st t when poll reach delay offset  jitter
>  ======================================================================
>  +GPS_NMEA(0) .GPS.            0 l   19   64  377  0.000 -1.680 253.141
>  oPPS(0)      .PPS.            0 l   10   16  377  0.000 -1.652   0.150
>  -k6x400      xxx.xxx.xxx.xxx  2 u   26   64  377  0.740  0.822   0.778
>  +me6000g     .PPS.            1 u   21   64  377  1.767 -0.439   0.309
>  -p4x2400c    xxx.xxx.xxx.xxx  2 u   22   64  377  1.893  0.611   0.520

David,

Thanks for the details.  My (rather limited) understanding was that the 
atom driver was simply a filter on an existing PPS signal, and therefore 
you would need a driver which knew about the LPT port and could detect and 
use its PPS signal.  Which driver does that I don't know, as I've never 
used one.

> Now NMEA(0) 92u/6u and PPS(0) 75u/2u, 60 minutes after ntpd restarted.

Are these jitter/offset figures?  Do I gather that the 253 milliseconds 
NMEA jitter was at the start, and it's now 6 microseconds?  Why so bad at 
the start, or was that simply the first reading?  But it can't be the 
first reading as it shows Atom sync, which was 7 minutes after the start. 
The "billboard" NMEA jitter figure puzzles me!

Cheers,
David 




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