Re: [PATCH net-next 2/3] dt-bindings: net: micrel: Configure latency values and timestamping check for LAN8814 phy

Andrew Lunn
2022-03-08T18:10:24Z

> > So this is a function of the track length between the MAC and the PHY?
>
> Nope.
> This latency represents the time it takes for the frame to travel from RJ45
> module to the timestamping unit inside the PHY. To be more precisely,
> the timestamping unit will do the timestamp when it detects the end of
> the start of the frame. So it represents the time from when the frame
> reaches the RJ45 to when the end of start of the frame reaches the
> timestamping unit inside the PHY.

I must be missing something here. How do you measure the latency
difference for a 1 meter cable vs a 100m cable? Does 100m cable plus
1cm of track from the RJ45 to the PHY make a difference compared to
100m cable plus 1.5cm of track? Isn't this error all just in the
noise?

Andrew