netdev - Re: Extending socket timestamping API for NTP

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Date:   Thu, 09 Feb 2017 16:33:19 -0800
From:   Denny Page <dennypage@...com>
To:     sdncurious <sdncurious@...il.com>
Cc:     Miroslav Lichvar <mlichvar@...hat.com>,
        Richard Cochran <richardcochran@...il.com>,
        netdev <netdev@...r.kernel.org>, Jiri Benc <jbenc@...hat.com>,
        "Keller, Jacob E" <jacob.e.keller@...el.com>,
        Willem de Bruijn <willemb@...gle.com>
Subject: Re: Extending socket timestamping API for NTP


> On Feb 09, 2017, at 11:42, sdncurious <sdncurious@...il.com> wrote:
> 
> I am still at a loss as to why transpose is required in case of HW
> time stamping. If STF is used for both Tx and Rx time stamping the
> timing is absolutely correct.

Perhaps this will help. The specific transposition is:

  transposed_timestamp_ns = timestamp_ns + (frame_len_bits * 1000000000) / (interface_speed * 1000000)

The transposition is applied to received timestamps only.

Denny