> -----Original Message-----
> From: Richard Cochran <richardcoch...@gmail.com>
> Sent: Tuesday, August 03, 2021 8:48 AM
> To: Aya Levin <a...@nvidia.com>
> Cc: Eran Ben Elisha <era...@nvidia.com>; Moshe Shemesh
> <mo...@nvidia.com>; Saeed Mahameed <sae...@nvidia.com>; linuxptp-
> de...@lists.sourceforge.net; tariq Toukan <tar...@nvidia.com>
> Subject: Re: [Linuxptp-devel] [RFC] ptp4l: improved-accuracy hook
>
> On Tue, Aug 03, 2021 at 02:31:25PM +0300, Aya Levin via Linuxptp-devel wrote:
> > PTP accuracy is increased when the HW time-stamp is taken as close to the
> > network wire as possible. In an effort to improve the time-stamp accuracy,
> > we consider extending the ptp4l. I would like to receive your feed-back on
> > the suggested below:
>
> This idea doesn't make any sense to me.
>
Why does there need to be a hook at all? The driver is literally the one
responsible for reporting the timestamp value. If the driver has some
mechanism, knowledge, or other method to allow it to determine the more precise
timestamp, it should simply implement this within the driver and report it. The
only possible exception I've seen is the asymmetry measurement, which drivers
*could* apply themselves, but is easier to just statically measure and store in
the PTP config.
For an example of such a setup, you could take a look at the ice driver code
for E822 devices which was recently posted to Intel Wired LAN. This hardware
has a mechanism to measure the impact caused by various parts of the PHY and
compensate timestamp values for this inaccuracy. When enabled, the timestamp
accuracy is improved. It's done all within the driver and hardware, and does
not need to modify ptp4l to achieve this.
> > I would like to push an infra structure hook to the ptp4l. This hook allows
> > vendors to estimate the HW time-stamp closer to the actual transmission and
> > reach better accuracy. The hook will receive the HW timestamp as an input
> > and will be able to manipulate it.
>
> Why don't the vendors simply provide ONE time stamp, the one which is
> most accurate?
>
> Nobody wants less accurate time stamps.
>
> Thanks,
> Richard
>
Well... I would think that in some cases we might accept less accurate
timestamps when the cost to increase accuracy is too high...
_______________________________________________
Linuxptp-devel mailing list
Linuxptp-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/linuxptp-devel
