Re: PVXS IOC Philosophy

["Johnson, Andrew N. via Tech-talk" <tech-talk at aps.anl.gov>]

I agree with Kay, the original design of EPICS to use configuration of standard records instead of coding to develop your control system software, and configuring standard widgets into display files instead of writing code for a specialist GUI was shown to reduce the effort needed by a significant amount. You're re-using software that has been tested in production at many sites already, so most of the low-level bugs have usually been found and fixed before you start, and you don't have to continually redevelop software to do almost the same things. Even if you take advantage of the modularity that EPICS provides and write your own device/driver support or display widgets, there are frameworks which make them relatively easy to do and integrate.

 

We have occasionally heard horror stories in the past of non-EPICS control systems that have taken a huge amount of effort to integrate different subsystems together, whereas with EPICS as long as you've specified a good naming convention for the PVs those kinds of problems are a lot smaller if they even exist at all.

 

- Andrew

 

 

On 3/20/24, 11:43 AM, "Tech-talk" <tech-talk-bounces at aps.anl.gov> wrote:

 

I’d say the prevalent scenarios would still be IOCs with records, and PVAccess is then used just like Channel Access. That’s why we have normative types which mostly mirror the DBR_.. types, and clients like CS-Studio that can fairly transparently switch between the two protocols.

 

With PVAccess you do now have the option to use new types. It allows you to transfer site-specific data over the same protocol, but you can’t expect generic widgets to fully understand your data. That mostly means you need to create both the server and the client, which you can do in python etc.

 

The new ‘group’ feature does allow you to create custom types by on combining data from records, but for the client side you’re then again on the hook to create for example a python script to understand that custom data.

 

So bottom line the goal here should not be that every piece of information now needs to be placed in a newly developed data type with its own custom server and client. On the contrary, the existing record types, the normative types to read/write them, and generic clients like display managers are meant to fill most of your needs, as was the case with EPICS for the last 30 years.

 

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Dave Bracey via Tech-talk <tech-talk at aps.anl.gov>
Date: Wednesday, March 20, 2024 at 12:30 PM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] PVXS IOC Philosophy

Going forward, is the philosophy of PVXS to create PV’s programmatically, per the examples (i.e. https://mdavidsaver.github.io/pvxs/example.html#mailbox-server) ?

 

Or, is the idea of creating PV’s by providing record definitions and instances via DBD / DB files still intended to be relevant?

 

One can create a hybrid IOC (https://mdavidsaver.github.io/pvxs/ioc.html) and still take in DBD/DB files, but this doesn’t seem to really involve PVXS, at least from the developer’s perspective (other than the fact that QSRV2 makes it work).

 

As always, I may be completely wrong about any of that, so feel free to let me know.

 

Dave Bracey – Fermilab AD Instrumentation