[ntp:questions] Using different timebase for ntpd
Patrick.Loschmidt at gmx.net
Tue Mar 24 10:58:58 UTC 2009
> An external timebase has been implemented in two ways. The most
> desireable is via the kernel and an appropriate shared memory device
Hmm, I guess, that would mess up the whole kernel and it's time keeping.
If not necessary, I would like to avoid generating more troubles than
> An alternative way is to used a driver such as the KSI/Odetics
> TPRO refclock driver. There might even be a refclock driver for the old
> TrueTime TT-560, although Symmetricom gutted the TT product line when
> they ate them.
Ok, thanks for the hint, I'll have a look at that code.
> There are numberous gremlins in your project. If all you want to do is
> stabilize the motherboard timer oscillator, poke the timer pin with a
> stable stignal and let the kernel/NTP feedback loop do the discipline
> and interpolation.
As mentioned in my other posting from today, my final goal is to run NTP
with hardware timestamp support to have a fair comparison to IEEE 1588
for my PhD. (I guess, there won't be much difference, concerning
accuracy) Unfortunately, I couldn't find any implementations (maybe
there is a good reason ...?) so I'm trying it on my own.
I know how to get the timestamps from the network card into NTP but I
need the daemon to discipline the clock on the card to make it somehow
> If you want to do frequency discipline, you will need
> to engineer some critical loop parameters. See Chapter 4 in my book.
I'll certainly have, since I expect to run in control loop tuning problems.
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