On 22 August 2017 at 19:41, Richard Cochran <richardcoch...@gmail.com>
wrote:
> On Tue, Aug 22, 2017 at 06:11:49PM +1000, David Mirabito wrote:
> > Would a patch to only sanity check the offset when in ptpTimescale make
> > sense?
>
> Looking into 1588:
>
> 8.2.4.2 timePropertiesDS.currentUtcOffset
>
> In PTP systems whose epoch is the PTP epoch, the value of
> timePropertiesDS.currentUtcOffset is the offset between TAI and
> UTC; otherwise the value has no meaning.
>
Yep, that's where I originally got the idea that if we're not
PTP_TIMESCALE, then this offset is ignored.
Presumably in ARB offset from UTC doesn't/cannot matter.
So, yes, when ptpTimescale==ARB the "temporal vortex" warning is not
> meaningful, strictly speaking. Still it does help one to realize that
> the GM is borken, don't you think?
>
Could do. I haven't seen *lots* of the weird stuff GMs in the wild do, but
my first reaction was that when ptpTimescale==ARB, the 'foreign master not
using PTP timescale' message would have sufficed at alert something is
afoot, and action taken if that was not intended.
>
> I mean, already in 2006 the TAI-UTC offset was 33 seconds, and
> everybody should know this, especially people who manufacture GM
> clocks.
>
But when configuring for UTC to be broadcast, I don't feel doing using ARB
timescale
and currentUtcOffset==0 is necessarily shoddy. That's what my Endrun does
and IMHO is
the correct way - yet we still log both messages; one informational and the
other potentially
scary.
I wouldn't necessarily configure UTC scale myself, and an argument maybe
could be made that
such an option shouldn't exist, but given that ARB exists, throwing a
warning on the value
of a field that has no meaning may be overkill.
(Currently I'm talking with folks who feel that warning when PTP_TIMESCALE
is abused
to directly distribute UTC is overzealous because "no other clients
complain".. I agree with you that we should
continue to log and moan in that case.)
Thanks for your advice, we'll think on this a little longer and perhaps
submit a patch to the devel list
and discuss any merits there.
Cheers,
David M
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