Experimental Physics and
Industrial Control System

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<== Date ==>		<== Thread ==>

Subject:	Infinite FLNK loop
From:	"Daykin, Evan via Tech-talk" <tech-talk at aps.anl.gov>
To:	EPICS tech-talk <tech-talk at aps.anl.gov>
Date:	Mon, 6 Dec 2021 20:43:36 +0000

Hi Tech Talk,

I have a set of three records on my IOC which asynchronously send outputs to a hardware device, call them “A, B and C”. When one of these three processes, the other two should also process.

My normal idiom is as follows:

record(ao, "A")

{

…

field(FLNK, "B")

}

record(ao, "B")

{

…

field(FLNK, "C")

}

record(ao, "C")

{

…

field(FLNK, "A")

}

Which always works fine if the records are Soft Channels, since all three are in the same lock set and the loop is smart enough to terminate. In my case where all three go to (slow) hardware, this continues infinitely. I see here (https://epics.anl.gov/tech-talk/2006/msg00216.php) that this was known behavior in 2006, but I’d like to see if there are any alternatives or workarounds in the following 15 or so years.

Thank you,

Evan

Evan Daykin

Controls Engineer

Facility for Rare Isotope Beams

Michigan State University

640 South Shaw Lane

East Lansing, MI 48824, USA

Tel. 517-908-7678

Email: daykin at frib.msu.edu