[ntp:questions] Slow convergence of NTP with GPS/PPS

Unruh unruh-spam at physics.ubc.ca
Sun Oct 26 19:48:30 UTC 2008


malayter at gmail.com (Ryan Malayter) writes:

>On Sat, Oct 25, 2008 at 4:51 AM, David Woolley
><david at ex.djwhome.demon.co.uk.invalid> wrote:
>>> Of course not ( and the GPS18 only gives 1us accuracy anyway) but the OP
>>> wanted accuracy to 1ms, which is trivial for both the computer and the gps.
>>>
>> I think there have been reports that the 1 microsecond is actually a
>> conservative figure.

>Wouldn't the serial port itself prevent anything better than b	104 B5s
>because of the commonly used 9600 baud rate on the serial line? Even
>at the max possible (according to Garmin) baud rate of 38400, 26 B5s
>would seem to be the best possible. Or does the PPS signal not depend
>on the serial baud rate?

The PPS is on a separate line. It is NOT on the serial port. 

>I have just acquired a GPS18LVC and am starting to wade into
>configuring on FreeBSD, but I am not expecting anything better than
>100 B5s at 9600 baud.

That may be what you expect, but you can get it 1usec (1 micro second).

 




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