On 2015-03-06 06:00, etherlab-users-requ...@etherlab.org wrote:
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
According to Beckhoff:
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
Ref:
http://infosys.beckhoff.com/english.php?content=../content/1033/ethercatsystem/html/bt_ecbasics_implementation_dc_ethercatcoupling.htm&id=
http://www.beckhoff.com/english.asp?pc_cards_switches/cu2508.htm
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).
- Dave
--
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David Page, Chief Embedded Architect
Dynamic Systems Inc.
PO Box 1234
Poestenkill, NY 12140
Telephone: +1 (518) 283-5350 | Fax: +1 (518) 283-3160 |
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