[ntp:questions] NTP server with Garmin GPS 18 LVC

David Lord snews at lordynet.org
Thu Dec 19 20:46:59 UTC 2013

unruh wrote:
> On 2013-12-19, David Lord <snews at lordynet.org> wrote:
>> Adrian P wrote:
>> .....
>>> Everywhere is written that FreeBSD is the best OS for time keeper,
>>> since its kernel supports nanosecond accuracies. However, if GPS 18x
>>> LVC PPS signal has only microsecond accuracy, then I suppose there is
>>> no point on using FreeBSD, any linux would be okay as well. So what do
>>> you think, looking from NTP point of view only, is this nanosecond
>>> accuracy the only reason why someone would use FreeBSD, or there are
>>> some other reasons as well? I see you have experience with all kind of
>>> OSes.
>> I think the combination of hardware used is at least as important
>> as the OS.
>> <http://www.febo.com/pages/soekris/> 100ns accuracy
> AGreed. But their comparison is strongly cooked. At least on my system,
> the serial port interrupt performace is far better than theirs--
> something like 2 us, not the 50us they are showing. Certainly 100ns is
> better, but more like one order of magnitude, not more than 2. 

It might not be very clear but PPS to serial port isn't used
other than as a comparison, ntpd has been modified to use the
Elan Timer with PPS input to the GPIO.

I have a couple of motherboards with chipsets that have higher
resolution timestamping but the GPIO pins aren't accessible.


>> <http://www.synclab.org/radclock/> An alternative to ntpd
>> David

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