minpoll=maxpoll from 1 to 7

Hal Murray hmurray at megapathdsl.net
Thu Sep 22 02:24:31 UTC 2016

Nice work.  Thanks.

Would you please remind us about what the PPS setups on those systems are.  
(I think you said the Xeon has a USB setup.)

And what do the column headings really mean?

Do you have a recipe for generating that data?  I expect it comes from 
ntpviz, but what do I type?  Is there anything interesting on the graphs? ...

For things like this, there is usually a tradeoff.  If you sample too close 
together (short poll) the errors are dominated by the accuracy of the 
measurement.  If you sample far apart, the underlying clock is changing while 
you are measuring it.  That leads to the classic V shape for ADEV graphs.  
The bottom of the V is usually the best place to measure.

For a good PPS (GPIO or real serial port) that works out to be 1 second or 

For PPS over USB things get messy because the error may not be Gaussian.  If 
you don't hit one of the ugly hanging-bridge cases, more measurements help to 
average out the noise.

These are my opinions.  I hate spam.

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