unruh wrote:
On 2013-12-19, David Lord <sn...@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.
David
<http://www.synclab.org/radclock/> An alternative to ntpd
David
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