Re: SNL question to the community

[Pierrick M Hanlet via Tech-talk <tech-talk at aps.anl.gov>]

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
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