Experimental Physics and
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<== Date ==>		<== Thread ==>

Subject:	Making mbbo record write string value instead of index
From:	"Sobhani, Alex via Tech-talk" <tech-talk at aps.anl.gov>
To:	"tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Date:	Fri, 26 May 2023 15:01:50 +0000

I want multiplexor-like functionality with epics records, where the user can select from a number of PVs to display using a selector PV, and then an output PV displays whatever PV was selected.

My current implementation is this:

record(mbbo, "mot:select"){

field(ZRST, "q8i:ai1 CP")

field(ONST, "q8i:ai2 CP")

field(FLNK, "mot:copy")

}

record(stringout, "mot:copy"){

field(OMSL, "closed_loop")

field(DOL, "mot:select")

field(OUT, "mot:pos.INPA CA")

field(FLNK, "mot:pos")

}

record(calc, "mot:pos"){

field(CALC, "A")

}

The mbbo record allows the user to select his choice using a combobox widget in CSS, and then the value of the selected PV is displayed in the mot:pos record.

This works, but I am wondering if this can be done using two records instead of three. I attempted the following:

record(mbbo, "mot:select2"){

field(ZRST, "q8i:ai1 CP")

field(ONST, "q8i:ai2 CP")

field(OUT, "mot:pos2.INPA CA")

}

record(calc, "mot:pos2"){

field(CALC, "A")

}

But this just ends up writing the index of the selection (0 or 1) to mot:pos2.INPA, instead of the pv link ("q8i:ai1 CP" or "q8i:ai2 CP"), even though "dbgf mot:select2.VAL" returns "q8i:ai2 CP".

This is not the behavior I would expect because the documentation says:

"If the OUT output link specifies a database link, channel access link, or constant, then the DTYP field must specify either one of the two soft device support modules-- Soft Channel or Raw Soft Channel. Soft Channel writes the value of VAL to the output link, without any conversion, while Raw Soft Channel writes the value from RVAL after it has undergone the above conversion."

https://epics.anl.gov/base/R7-0/6-docs/mbboRecord.html

And when I do "dbgf mot:select2.DTYP" it returns "Soft Channel".

So why does the VAL field get converted to an integer?

Alex

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ANJ, 28 May 2023

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System