Re: [Linuxptp-devel] [PATCH RFC v3 02/10] Introduce the power profile.

[Olivier D. <oli...@or...>]

Hi,

The 11/10/2021 06:42, Richard Cochran wrote:
> 
> On Wed, Nov 10, 2021 at 12:59:33PM +0100, Olivier Dautricourt wrote:
> 
> > I had the feeling that power profiles attributes such as
> > totalTimeInaccuracy should be properties of the clock.
> > In case of a simple BC or jbod, all the ports need to share the
> > same inaccuracy.
> 
> If two ports have different HW, like one MAC and one PHY with
> differing time stamping inaccuracy, then the values will be
> different.
> 
> In addition, using a port attribute allows having the 2011/2017
> flavors running on different ports.
> 
> > This way, we don't rely on users to forward the inaccuracy between ports
> > with management tlvs.
> 
> This series treats the values as static.  There is no automatic
> update.  The profile does not specify how to automatically calculate
> the values.  On the contrary, it recommends a one time calibration
> "during network engineering stage":
> 
>     Overall time inaccuracy should be calculated during network
>     engineering stage based on device specifications and network
>     design. All time inaccuracy values used in this calculation should
>     be based on the manufacturer's specified device time inaccuracy
>     values, along with the source time inaccuracy of the recognized
>     standard time source.
> 
Ok, this part is confusing as the standard says above:

On grandmasterTimeInaccuracy:
	"This value should be updated in real time, as conditions
	change"
and:
	"TotalTimeInaccuracy shall be automatically incremented by TCs
	and BCs"

Suggesting that BC/TC inaccuracy should be taken into account
automaticaly.
> > We also know that the totalTimeInaccuracy will
> > always be the sum of other fields.
> 
> No, it is one or the other.  Either you have:
> 
> reserved1 = grandmasterTimeInaccuracy = 0, totalTimeInaccuracy != 0   2017 flavor
> 
> or
> 
> grandmasterTimeInaccuracy != 0, networkTimeInaccuracy != 0            2011 flavor
> 
My understanding of the 2011/2017 compat is that you can sum
reserved1 and totalTimeInaccuracy to compute an equivalent
totalTimeInaccuracy coming from a 2011-compatible end device. (C37-238 Annex B)
But i have not read the 2011 standard thoroughly as we were focused on
61850-9-3 (utility).


Thanks,

-- 
Olivier