Re: SNL question to the community

["Vodopivec, Klemen via Tech-talk" <tech-talk at aps.anl.gov>]

Ralph,

 

Having a generic solution/API for EPICS process database like you and Michael propose would be beneficial for other projects as well, ie PyDevice where a lot of people now use PyEpics when interfacing with PVs inside same or remote IOCs.

 

-- Klemen

 

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Pierrick M Hanlet via Tech-talk <tech-talk at aps.anl.gov>
Date: Saturday, March 8, 2025 at 11:29 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>
Subject: [EXTERNAL] Re: SNL question to the community

Thanks Ralph, I essentially have the same model as you see it; I'm glad to know that I'm not out on a limb in my thinking. I like Michael's idea, analogous to aSub, which made its way into base. Cheers, Pierrick On 3/8/25 04: 23, Ralph Lange

Thanks Ralph,

I essentially have the same model as you see it; I'm glad to know that 

I'm not out on a limb in my thinking.

I like Michael's idea, analogous to aSub, which made its way into base.

Cheers,

Pierrick

On 3/8/25 04:23, Ralph Lange via Tech-talk wrote:

> 

> [EXTERNAL] – This message is from an external sender

> 

> Hi Pierrick,

> 

> This has been discussed in the past... on Tech-Talk and at meetings.

> Ben, the current author/maintainer of SNL/SNC, has stated on tech-talk 

> that he doesn't see an easy straightforward way to integrate SNL with 

> PVA without fundamentally changing the concepts of SNL.

> 

> But. SNL/SNC is the best-tested and best-documented EPICS module. 

> (Most of that is Ben's work. Kudos!) It is in use at almost every 

> installation and nothing could replace it any time soon. It will not 

> go away.

> 

> I see the sequencer's strength in implementing small state machines, 

> close to the device, running on an IOC. Ramps, switch-on/switch-off 

> procedures, slow feedback-type applications, that genre.

> Complicated procedure sequencers, driving whole sub-systems using 

> 1000s of PVs across many IOCs - that's the scope for high-level 

> operations sequencers like oac-tree. For these applications, SNL/SNC 

> doesn't scale well enough and has conceptual limitations.

> 

> With Channel Access slowly being sunset, the current SNL/SNC as a pure 

> CA client will not be maintainable forever.

> The more I think about it, the more I like Michael Davidsaver's idea: 

> Make SNC/SNL directly work with the EPICS process database, with no 

> Channel Access involved. That would cut down the code base, 

> significantly reduce complexity, and put the sequencer exactly where 

> it belongs - inside the IOC, complementing the process database as a 

> local tool to implement finite state machines. If state machines need 

> access to resources outside the IOC, local proxy records can do the 

> remote connection - using standard PVA or CA provided by Base for 

> cross-IOC links.

> 

> Cheers,

> ~Ralph

> 

-- 

-- Pierrick Hanlet

+1-630-840-5555 office

+1-312-687-4980 mobile

=== "Whether you think you can or think you can't, either way, you're correct" -- Henry Ford