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<div class="moz-cite-prefix">On 2015-03-06 06:00,
<a class="moz-txt-link-abbreviated" href="mailto:etherlab-users-request@etherlab.org">etherlab-users-request@etherlab.org</a> wrote:<br>
</div>
<blockquote
cite="mid:mailman.1.1425639601.13661.etherlab-users@etherlab.org"
type="cite">
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 slave</blockquote>
<br>
According to Beckhoff:<br>
<blockquote type="cite">Note: for cable redundancy two Ethernet
ports are used. However, the combination of distributed clocks
(DC) and cable redundancy is only possible with device CU2508, see
associated device documentation<br>
</blockquote>
Ref: <br>
<a class="moz-txt-link-freetext" href="http://infosys.beckhoff.com/english.php?content=../content/1033/ethercatsystem/html/bt_ecbasics_implementation_dc_ethercatcoupling.htm&id=">http://infosys.beckhoff.com/english.php?content=../content/1033/ethercatsystem/html/bt_ecbasics_implementation_dc_ethercatcoupling.htm&id=</a><br>
<a class="moz-txt-link-freetext" href="http://www.beckhoff.com/english.asp?pc_cards_switches/cu2508.htm">http://www.beckhoff.com/english.asp?pc_cards_switches/cu2508.htm</a><br>
<br>
I could see how it would be possible to make DC work with master
software only, but some considerable delay would be involved to
identify the new topology. (Process data, on the other hand can just
be sent out both master ports with zeroed input PDOs and then
bitwise ORed on receipt).<br>
<br>
- Dave<br>
<br>
<div class="moz-signature">-- <br>
<hr>
David Page, Chief Embedded Architect<br>
Dynamic Systems Inc.<br>
PO Box 1234<br>
Poestenkill, NY 12140<br>
Telephone: +1 (518) 283-5350 | Fax: +1 (518) 283-3160 | </div>
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