[ntp:questions] Using different timebase for ntpd

Patrick Loschmidt 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 
> driver.

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.

Kind Regards,

More information about the questions mailing list