[time-nuts] 1PPS users?

[Hal Murray]

bob at evoria.net said:
> So, if an NTP user can get his time fix directly from a noisy receiver, who
> actually needs a time-accurate, low jitter 1PPS pulse?

Most kernels have an option to capture a time stamp from a PPS signal at 
interrupt time.  That is much more accurate than the timing you get from user 
mode on a serial data stream.

There is also a mode where the whole NTP PLL processing is done in the 
kernel.  I don't see why that should make as much of a difference as it does, 
but I haven't tracked down the details.  (It's not in the typical Linux 
kernel.  You have to build your own.)


Most low cost GPS receivers have crappy timing on the serial port.  Really 
crappy.  It wanders with a time scale of hours so you can't filter out the 
jitter by averaging for a minute or two.  PPS on that sort of unit makes it 
much more interesting.


-- 
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