Re: Communicate between XML-RPC system and EPICS Channel Access?

[Andrew Johnson <anj@aps.anl.gov>]

HI Russell,

On 03/01/2018 07:50 PM, Russell Kackley wrote:
> Subaru Telescope has a new laser system coming in soon and there is a
> proposal to use EPICS software from Keck and Gemini to control the
> laser. Subaru, Keck, and Gemini are going to be sharing laser system
> spare parts, so it would make sense for us to also share the laser
> control software. However, we don't currently have EPICS installed
> anywhere at Subaru. We currently have our Observation Control System
> (OCS) using XML-RPC to communicate between processes distributed among
> various computers. We really need the OCS to be able to communicate with
> the laser system, i.e., send control messages from the XML-RPC based
> system to EPICS Channel Access and receive status back along the same path.
> 
> My question is: has anyone done any work to enable communication between
> an XML-RPC system and EPICS Channel Access? Thanks in advance for any
> suggestions.

If Maren's suggestion of "tide" doesn't work out I wouldn't expect any
major technical problems writing something that translates XML-RPC calls
into CA operations. Any complexity is more likely to be at the
application layer, where you have to work out what CA operations are
needed on which channels as a result of each particular RPC call.

I don't think it likely that you could create a generic solution though,
you'll probably have to have someone understand how the laser system
expects to be controlled by writing to and monitoring or reading its
various PVs, then translate the XML-RPC operations that your OCS wants
to use into the appropriate CA operations.

Maybe those translations could be encoded into a set of tables read from
a configuration file and run by some generic translator, but I suspect
the needed complexity might require a custom code solution. That code
could probably be written in C/C++, Java or even Python though.

If you haven't already you might consider approaching Observatory
Sciences or even CosyLab for commercial help, they both have experience
in EPICS and telescope controls (although not necessarily together).

HTH,

- Andrew

-- 
Arguing for surveillance because you have nothing to hide is no
different than making the claim, "I don't care about freedom of
speech because I have nothing to say." -- Edward Snowdon