Re: Hardware Timestamping Problem

[Guenter Ebermann <guenter.ebermann () googlemail com>]

> Am 09.06.2016 um 15:47 schrieb Michael Richardson <mcr () sandelman ca>:
>
> Guenter Ebermann <guenter.ebermann () googlemail com> wrote:
> > Hardware timestamping of sending/receiving buffer descriptors is done
> > by NIC.
>
> Receiving I understand.
>
> Are you sure that the hardware is going to timestamp sent packets, and then
> turn around and send the back to the kernel?

Yes, the driver must monitor tx descriptor consumption by hardware anyways.
E.g. Freescale enhanced three speed ethernet controller (eTSEC) can timestamp
send buffers - it writes the timestamps to the beginning of the buffer descriptor.
You use such a controller feature to implement PTP (IEEE 1588).

For Linux drivers supporting hardware timestamping see [1], chapter 5.3.2.

The i350-T4, handled by Linux driver igb, is also supported (igb_ptp.c).
It seems it does also timestamp tx buffers.

[1] http://linuxptp.sourceforge.net/
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