On 30 June 2014, quoth Knud Baastrup:
> I am still not able to identify a scenario where the EtherCAT master use
> concurrent CoE requests towards the same slave. I know that both master
> and slave FSM have CoE FSM instances, but their usage are controlled by
> the master FSM in dedicated states that should prevent concurrent
> access. Do any of you have any likely concrete scenario this can happen?
The case when it does happen with current master code is the same as the one
Frank outlined when he provided his original patches.
Specifically, after doing a network scan and basic configuration (either to
PREOP or to OP depending on the application state), fsm_master goes into an
idle loop where one of the things it will do is to read the SDO dictionaries of
each slave that it hasn't previously read. This will execute concurrently with
any other SDO request, whether that's coming from the command line tool or an
application using ecrt_master_sdo_{down,up}load, or a realtime SDO request
object.
Most of the time you can get away with that, as you're probably accessing
different slaves, or you don't start the application until the network is
stable and fully scanned (though bear in mind that it'll trigger a rescan if
the network is disrupted at all). Sometimes you don't get away with it though
and you'll get "unexpected response" errors and other issues.
Regards,
Gavin Lambert
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