| Re: [4diac-dev] Support for OPC UA events |
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Hi Matthias, it sounds very interesting. We were also thinking in the same direction. I know, there was some ongoing work on implementing OPC UA Events in forte [1], but I don't know its current status.
I would propose to use SUBSCRIBE_0 (and PUBLISH_0 on the server side) for handling OPC UA events. I don't think there should be a generic FB for state machines as I can imagine those will be quite different in each
particular case. But if we have methods and events support, one can already create a subapp to control a state machine.
One other thing that is missing in forte but might be useful for controlling an OPC UA state machine is references support. Events can carry some data. In OPC UA it is realized by a reference from the Event instance
to an object, which client should check for updates, whenever an Event is triggered. For doing that, 4diac should be able to browse the OPC UA namespace and find out these kind of "bindings" and then create a subscription to this data (or simply read it after
Event notification occurs). But one can also add this manually on the first step, I see references as more like “nice-to-have”, not desperately needed. Here, for example, how I'd see an implementation for controlling an OPC UA Programs State Machine in 4diac
Each Transition Event gets a Subcribe_0 with an ID opc_ua[SUBSCRIBE_EVENT;<endpoint_address>#;<browse_path_to_object>;ReadyToRunning] Each control method gets a Client FB with an ID opc_ua[CALL_METHOD;<endpoint_address>#;<browse_path_to_ method>] To sum up: I think, you’re on the right way of implementing it. Just subscribe to a particular event type -- as each of your StateMachine transitions will have its own type – and it should work. Something like ReadyToRunning
in case of OPC UA Programs. So you just specify the particular type in your SUBSCRIBE ID, and you’ll have one SUBSCRIBE FB per each transition (see my example above). Btw, you don’t have any RD_x in SUBSCRIBE_0, so I was a bit confused when you describe that
you will have some flags for each RD. This will be a generic implementation of OPC UA Events in forte without any state machines specifics. Hope it makes sense and helps somehow. Cheers, Kirill [1]
https://bugs.eclipse.org/bugs/show_bug.cgi?id=553521 -----Original Message----- Hi, we want forte connect to a opc ua statemachine and gather the transition events of it. To interact with opc ua statemachines the mechanisms of method calls (supported by forte) and events (currently not supported by forte) are needed. I've done a little prototype implementation and now able to get notified when a event is triggered on an opc ua object. (I don't filter the event type or any other member of the event type). Now I'm thinking about the interface, how it could be used in the 4diac ide. Currently I'm using a SUBSCRIBE_0 FB with ID: opc_ua[SUBSCRIBE_STATEMACHINE;<endpointurl>;<browsePath to Object I want to monitor>;<NodeId of EventType I'm interested in>] Next step would be to map the opc ua TransitionIds to the RD_1 ...RD_n outputs as boolean flags for signaling which transitionEvent has been fired. You see, the interface is quite narrowed for supporting statemachines. Do you think, this can be done in a more generic way? Best regards, Matthias. _______________________________________________ 4diac-dev mailing list To unsubscribe from this list, visit
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