Re: Going full PVA?

[Timo Korhonen via Tech-talk <tech-talk at aps.anl.gov>]

Hi Tom,

 

We at ESS are aiming to go full PVA. So far it is proceeding quite well, although it will take some time before we get to be 100% “CA-free” – if ever, even if that is still the goal.

I do not consider it too bad if we have some fringe uses of CA left (e.g., CA links in IOC databases) as long as our IOCs and the application level all runs on PVA. That we have pretty much achieved, there is some work left in updating legacy IOCs that have been developed before EPICS 7 was available. In theory one could even run a PVA server on those but we rather update them to more recent releases, for many other reasons besides PVA compatibility.

 

If your legacy device is an IOC (i.e., you are talking to that device via an IOC), then there are little or no issues. Just take a recent EPICS base and run your IOC on it. This obviously assumes that you have all the pieces available to recompile the IOC. But if you do, this is straightforward to do.

However, if you have an embedded IOC that is stuck to some older EPICS version, then it will be difficult. For this reason we avoid using vendor EPICS integrations that used to be popular some time ago and rather use StreamDevice/Modbus/asyn or similar to integrate those, and do EPICS integration on our side.

 

I am not aware of any CA<->PVA translators; we have not seen the need in our applications. I am not even sure how much sense that would make (IMHO).

 

As a new facility we have been able to start more or less from scratch, very little, if any, legacy to support, so we probably have had a simpler journey than most others would have.

 

Best regards,

 

Timo

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Stainer Tom via Tech-talk <tech-talk at aps.anl.gov>
Reply-To: Stainer Tom <Tom.Stainer at sckcen.be>
Date: Tuesday 8 June 2021 at 09:52
To: "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Subject: Going full PVA?

 

Dear tech-talk,

 

I am looking for some general advice and expertise on CA vs PVA in practice. After reading about the differences and the theoretical points of view, I am now interested to learn about the practical side of things.

Specifically, if one were to go full PVA (no CA), what pitfalls or problems would I encounter?

 

For example, if I have to support a legacy system or device which already has a CA interface how difficult is it to port or map this to PVA?

Do CA <-> PVA translators exist in the community?

 

I am of course aware of certain extensions and libraries not yet supporting PVA, but my question relates more to the hardware side of things and networking.

 

Maybe an additional question which might prove helpful – has anyone ever gone full PVA?

 

The prospect of using one protocol is very much more appealing and PVA seems to be the new and improved protocol. Particularly I would like to take advantage of things like RPC and the “smart database”.

 

I realize open questions like these can sometimes yield some varied responses but any advice would be greatly welcomed.

 

Kind regards,

Tom