[etherlab-users] Redundancy support

[Gavin Lambert]

Yesterday, I quoth:
> Possibly some of this is related to the weird linked-but-not-linked
behaviour
> when the backup link is connected but unneeded (described in my prior
email).

Well, I've fixed that now (it was an incorrect assumption in the EtherCAT
driver mods), but it hasn't helped the delay measurements.


I guess the main problem is that the measurement code seems to assume that
the receive timestamps are all updated from the same packet.  But in a
redundant topology, especially with no network breaks, some of the ports
don't actually receive packets, or the timestamps within a single slave are
updated from different packets traversing.  So a port might be "open" but
the timestamp may not have updated or may be from a packet sent at a
different time from what you're expecting.

And the topology calculations assume that the packet is always entering from
port 0, which isn't always true with a redundant setup.  (I can understand
why -- I've had a think about it and it's quite a tricky problem, especially
given some of the limitations on data available from the slaves.)