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

David Lord snews at lordynet.org
Sat Feb 6 12:00:49 UTC 2010

David J Taylor wrote:
> "David Lord" <snews at lordynet.org> wrote in message 
> news:7t3ms3Fqe0U1 at mid.individual.net...
> []
>>>> Somehow I think I might be in sync with wrong edge of PPS.
>>> Why?
>> That would put pps out, but I'd have guessed by only 100ms
>> if that's default.
> Yes, David, according to the Technical Specifications the default is 
> 100ms.  I'm surprised that the parallel port is as bad as it appears to 
> be - perhaps some software is getting in the way of the interrupt path. 
> No chance it's polled rather than generating an interrupt, I suppose?

A few us isn't bad from PPS unless I'm supposed to use the -350 ms
from nmea via RxD.

Note that the PPS via serial and parallel are both converging to
same < 10us and it's only when serial DCD is disconnected that
GPS_NMEA shoots off by -350us. PPS via parallel is well within
spread of the servers on network

! after 10 hours
!    remote    refid   st t  reach offset jitter
! +GPS_NMEA(0) .GPS.    0 l   377  29.189 21.691
! oPPS(0)      .PPS.    0 1   377  -0.009  0.004
!  serv1       serv2    2 u   377   1.144  0.526
!  serv2       .INIT.  16 u     0   0.000  0.000
!  serv3       serv2    2 u   377  -0.018  1.740

Ouch, the server that remained at .INIT. was out for a good
reason, I'd been debugging a problem with pre release of mail
server prior to going back to PPS over parallel so had changed
hostname to be same as that of mailserver which also happens
to be serv2. Changed hostname back, restart ntpd, then serv2
shows refid of .PPS. (that's pps from MSF not GPS).


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