Experimental Physics and
Industrial Control System

"[email protected]" <[email protected]> · Thu, 5 Apr 2018 12:45:17 +0000

> 	2. Can I use this introspection interface to retrieve the name of a
> service and its parameter list to compose a RPC during runtime by following
> Marty's approach?
> 
> I suspect that the answer for pvAccess itself is no.
> 
> But even if the answer is no a channelRPC service can implement it's own
> query service that describes itself.
> But it must describe itself via pvData.

That is the approach that Diamond has taken in its continuous scanning middleware:

http://pymalcolm.readthedocs.io/en/latest/reference/structure.html

We define a Block to be a container for a number of Methods and Attributes. Attributes are represented by NTScalars, NTScalarArrays and NTTables, but with their metadata abstracted to separate Meta objects. These same Meta objects are used to describe the arguments that a Method should be passed when doing an RPC on it, and the structure it will return. We implement this in Python, exposing the structures either over pvAccess (currently with a Diamond specific fork of an old version of pvaPy, but we are working on this) or as JSON over websockets.

Thanks,
Tom

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System