On Mon, Jan 08, 2018 at 03:56:29PM +0100, Miroslav Lichvar wrote:
> You mean asymmetry added by boundary clocks on the path to the
> grandmaster?
Yes, or from any other source at all.
> One thing I find odd is that the sync message doesn't have a TLV
> attached too. Does the specification say anything about that?
No, and I noticed that too. The original 1588 standard makes sure
that all event messages have the same length, but this extension does
break that. I'll mention that to Meinberg, but I think they have
already deployed this as is.
> Are transparent clocks expected to update the correction field in
> messages with TLVs?
Good question. 1588 says:
13.2 General message format requirements
All messages shall have a header, body, and suffix. The suffix may
have zero length.
and:
13.4 Suffix
An application layer message is suffixed by a contiguous sequence
of zero or more entities of data type TLV ... Nodes should append
no TLV entity to event messages.
NOTE -- Appending TLV entities to an event message is likely to
change the transmission delay suffered by the messages in passing
through non-PTP bridges.
Notice it only says "should" and not "must not". So I would say that
TCs must allow TLVs in any message.
> This didn't work for me with HW timestamping. I had to modify also
> pmc_create() to change the timestamping mode in the transport_open()
> call and set the ts_label in the interface struct.
Oops, I only tested with SW time stamping.
> However, is pmc the right place for this functionality? As the
> exchange does not use any management messages, it would probably make
> more sense to me if it was in a separate binary, or maybe it could be
> a special query mode of ptp4l which would just print the offset and
> exit (with the possibility that it could be later used for normal
> synchronization of the clock).
I put it into pmc because it seemed to be a management function, event
though it uses no management messages. If not there, then I prefer a
separate binary for this.
> There is a hack which detects that pmc is trying to send a message by
> checking for POLLOUT in events[1] and nfds == 2. It needs to be
> updated if the number of descriptors is increased.
(That is even more reason to make NSM its own binary ;)
Thanks,
Richard
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