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

[Wojciech Owczarek]

On Thu, 22 Oct 2020 at 01:53, Magnus Danielson <magnus at rubidium.se> wrote:

> Hi,
>
> Yeah, poor CPU time-stamping can be worse than network biases, but
> hardware time-stamping and careful use of good time-stamps handles most
> of the host issues. Then network biases becomes the dominant problem
> unless one does not have other implementation issues, and well, those
> are common, including dropping PTP packets aimed for processing. In one
> instance there was a rate-limit internal to the equipment that did the
> wrong thing. Slowly the implementation issues is being ironed out. I
> learn more of this than I want to.
>
>
The story of my life pretty much. Early PTP transparent clock switches were
two-step and software would handle PTP message corrections and PTP messages
indeed went to the CPU, so this was somewhat error-prone. Pretty much all
new higher-end Broadcom switching ACICs (OK, hardly home switch material)
have had PTP TC support completely in hardware for a number of years now,
with zero software control required. First TCs were mostly industrial
automation kit like Hirschmann, Moxa and what have you. Since Broadcom's
TCs (and BCs) hit the mainstream, PTP on the network side has been more
attainable than ever. But on the host side, it's still a minefield.


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Wojciech Owczarek