netdev - Re: Extending socket timestamping API for NTP

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Message-id: <97185563-83FD-46D6-B8CE-D3F236157D4D@me.com>
Date:   Fri, 10 Feb 2017 10:55:35 -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 16:33, Denny Page <dennypage@...com> wrote:
> 
> 
>> 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.


Before anyone else asks, yes, I know this can be reduced. :)