Re: [Linuxptp-users] Expected throughput of the ptp4l

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

On Tue, Mar 17, 2015 at 05:28:45PM +0000, Chandra Mallela wrote:
> 512 sync packets are a reasonable rate for frequency corrections. In case of ToD, the fractional HW arithmetic (2^-16) can give you capability to achieve the highest accuracy possible, if the stack can supply such fine-grained values.

AFAIK the Linux time stamping and clock interfaces are limited to
nanoseconds. As an excersise to see when things start to fall apart
sync rate of -9 may be interesting, but I'm not sure if it there is
any practical value.

> As for 'what is that supposed to achieve?', in ideal scenario, targeting 50pbb for CDMA is what I look at. I am further trying to analyze SyncE requirements from 1588 perspective, which seems too tough at this moment due to OS scheduling jitter itself.

Do you have any specifications on the clock stability and jitter?
Unless you are dealing with some very unstable clocks or large
jitters, with careful PI configuration keeping the frequency error
below 50 ppb shouldn't be difficult even at the default 1Hz sync rate.

-- 
Miroslav Lichvar