Re: [Linuxptp-users] Interpretation of ptp4l results

[Miroslav L. <mli...@re...>]

On Fri, Jun 19, 2015 at 07:53:52AM +0000, Chandra Mallela wrote:
> 
> 
> Hi Friends,
> 
> I would like to double-check whether my following interpretation is correct. Please elucidate me.
> 
> For the following ptp4l output, the ptp4l reports rms value and the max deviation from the mean offset. Thus, if I have to report the worstcase accuracy, I take the (rms+max). For example, , looking at the first line, I see that the maximum offset uncertainty/inaccuracy  observed is 2 +7 = 9ns. The maximum frequency uncertainty is (156403 + 7) pbb.

The max value is just the maximum measured offset in that interval. It
doesn't mean it's also the worst accuracy of the clock. There could be
an asymmetry in the network delay and ptp4l wouldn't know the clock is
actually behind or ahead of the time source. To evaluate the accuracy
you would to measure the error independendly from PTP, for example by
comparing PPS signal generated by the synchronized clock with the
reference on a scope.

-- 
Miroslav Lichvar