Hi Dave,
Yes, PVXS is evolution, not revolution.
That's also why our version numbers jumped from 3.16.x to 7.x back in 2017 — EPICS 7 is the combination of the IOC developments up to Base 3.16.2 with the new PVA protocol from what was then being called EPICS V4. We realized once V4 was
becoming functional that to support our existing users (who were also the employers of most of the core EPICS developers) we had to provide a path for upgrading existing IOCs and control systems, without forcing them to be significantly rewritten — none of
the US DOE sites would have been able to do that. Some work had been done to develop an EPICS V4 IOC (in Java), but it wasn't designed to be backwards-compatible at all and there was no way it could have ever run databases from an existing V3 IOC.
We are thus being careful to implement changes by evolution instead of revolution, and PVXS was how Michael Davidsaver chose to fix some of the major issues with the architecture and APIs implemented in pvDataCPP and pvAccessCPP. We haven't
decided how and when it might be integrated and included in official EPICS releases, but I'm sure it will happen sometime. Users who rely on on the pvDataCPP and derived APIs will continue to be able to build against and use those libraries, but there isn't
much development being done on them now.
Replacing the GNU make-based build system would be a revolution since there are so many existing IOCs and control systems based on it. We have considered a
proposal to permit builds using meson, and if enough members of the EPICS community express interest and offer to provide long-term effort to maintain an alternative build system we could include
one, but removing the existing build system would be hard to do given all the EPICS installations around the world that have thousands of applications, many with customized Makefiles and local build rules. Maybe AI…
- Andrew
On 3/20/24, 12:43 PM, "Dave Bracey" <dbracey at fnal.gov> wrote:
First, thank you everyone for the discussion, it is great to get more context filled in as I learn this stuff.
Andrew, to answer your question, I’m primarily after using the tech with the best future, so I was interested in PVXS just from that perspective. CA is not an issue.
I think my confusion stems mostly from reading the PVXS doc at
https://mdavidsaver.github.io/pvxs/ and noticing that it doesn’t mention DB-style “records” anywhere, but it does give examples of building PV’s programmatically at run-time. This caused me to wonder “is this the new way?”
But from you guys have been saying here, am I right to think that PVXS is mainly a replacement implementation of pvAccessCPP, etc. and is not intended to change things for the basic IOC developer?
From: Johnson, Andrew N. <anj at anl.gov>
Date: Wednesday, March 20, 2024 at 12:30 PM
To: Dave Bracey <dbracey at fnal.gov>, Kasemir, Kay <kasemirk at ornl.gov>, tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: PVXS IOC Philosophy
[EXTERNAL] – This message is from an external sender
Hi Dave,
When you say PVXS, are you really asking about building IOCs that provide both a Channel Access and PV Access server, or about using the specific PVXS implementation instead of the original pvAccessCPP?
You don't need PVXS to create IOCs that can talk the PVAccess protocol. PVXS started as a reimplementation of the original C++ client and server code for the PVA protocol but using a better internal architecture
and written in modern C++. It can communicate over IPv6 now, and future releases will be able to use TLS for much improved security, but those won't change the underlying IOC code significantly.
- Andrew
On 3/20/24, 12:06 PM, "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.
I guess I’m unsure what the value of PVXS would be in a scenario like that? If you are starting from a normal EPICS IOC project, and adding PVXS, what is PVXS doing for you? You are still defining your PV’s in
terms of records in DB files, etc.
I can see that if you are building an IOC for an embedded architecture, the EPICS build system adds value in being able to handle the different toolchains and build products, etc.
However, at the moment I’m looking at making a soft-IOC (i.e. on intel/amd64 linux), and I’m seeing the opportunity to use a simpler (and contemporary) build system and construct PV’s at run-time, rather than use
DBD/DB which need to be consumed at build.
I’m wondering if this is a compelling idea at all, or a poor idea?
From: Kasemir, Kay <kasemirk at ornl.gov>
Date: Wednesday, March 20, 2024 at 11:43 AM
To: Dave Bracey <dbracey at fnal.gov>, tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: Re: PVXS IOC Philosophy
[EXTERNAL] – This message is from an external sender
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
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- Re: PVXS IOC Philosophy Kasemir, Kay via Tech-talk
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- Re: PVXS IOC Philosophy Johnson, Andrew N. via Tech-talk
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