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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