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

Ryan Malayter malayter at gmail.com
Sun Oct 26 17:09:04 UTC 2008

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 ≈104 µs
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 µs
would seem to be the best possible. Or does the PPS signal not depend
on the serial baud rate?

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

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