[time-nuts] IEEE 1588 PTP support on raspberry pi 4 compute module

[Wojciech Owczarek]

Hello Bob,

On Thu, 22 Oct 2020 at 01:53, Bob kb8tq <kb8tq at n1k.org> wrote:

> Hi
>
> Simply that you can get into the 10’s of microseconds (done in many times)
> with
> NTP. If the local LAN is streaming video, it needs 1588 switches / routers
> to do
> better than that.
>

That is all true, however not every single frame will hit those worst
latencies. With careful filtering and high message rates, lucky packets can
be picked out from the rest. The result shows more jitter than NTP, but
overall tighter bounded and with significantly less wander. Also, a 10 us
offset reported does not necessarily mean it's been passed to the clock
discipline and will cause the clock to swing by that, but consume enough of
those and it will, yes.

Well. your lab and my home LAN produce *very* different results …..
>
> Bob
>

Again - I can only nod until I produce some results :-) I tend to ignore
self-reported offset figures from software, so unless a thing has a 1PPS
output, I am very sceptical. The NICs I test with, do.