Yo Hal! On Wed, 21 Sep 2016 19:24:31 -0700 Hal Murray <hmur...@megapathdsl.net> wrote:
> Nice work. Thanks. I wish it brought more clarity... > Would you please remind us about what the PPS setups on those systems > are. (I think you said the Xeon has a USB setup.) https://pi3.rellim.com/day/ https://rellim.com/ntpstats/day/ Notes on the system config, and links to the ntp.conf are on those pages. > And what do the column headings really mean? Those match the headings on the ntpviz pages, links just above. > 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? ... I just copy the numbers off the graphs. I think I'll need to automate it some more. > 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. Yeah, I'm just surprised at how different the Pi3 and the Xeon are. > For a good PPS (GPIO or real serial port) that works out to be 1 > second or less. SO far I'm seeing 4s as the best on the Pi3. > 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. Yeah, not even started to look at that yet. What I see is the USB phase locks to the PPS and the results are 'too good'. RGDS GARY --------------------------------------------------------------------------- Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703 g...@rellim.com Tel:+1 541 382 8588
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