[etherlab-dev] Support for multiple mailbox protocols

[Gavin Lambert]

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