Experimental Physics and
Industrial Control System

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

Subject:	Re: CA output links not working with PINI=YES?
From:	"Mooney, Tim M. via Tech-talk" <tech-talk at aps.anl.gov>
To:	"Johnson, Andrew N. via Tech-talk" <tech-talk at aps.anl.gov>, "Benjamin Franksen" <benjamin.franksen at helmholtz-berlin.de>
Date:	Thu, 5 Mar 2020 19:28:25 +0000

I had a similar problem, and solved it by using a scan task to trigger processing of the record whose operation could not work until channel access was up. (EPICS starts scan tasks after channel access.) Here's a code fragment from the table_soft.vdb database in the synApps optics module:

initLastMotor processes once, after channel access is up, and then sets its SCAN field to "Passive"

---snip---

# Strategy: We need to find out when all motors have finished executing a move

# that we started. To do this without a race condition, we set a gate PV to

# "open", write to motors, and then have the last motor written to set the gate

# PV to "closed" when it finishes. But we don't know which motor will be the

# last motor written to, because the table record can work with fewer than six

# motors, and we don't know which motors don't actually exist.

# $(P)$(Q):lastMotor figures this out at init time.

# Evidently, $(P)$(Q):lastMotor's PINI==RUNNING field isn't getting

# $(P)$(Q):closeGate.INPA initialized. This seems bulletproof.

record(scalcout, "$(P)$(Q):initLastMotor") {

#field(TPRO, "1")

field(SCAN, "10 second")

# Note that this must be a CA link so it can read a link field

field(INAA, "$(P)$(Q):closeGate.INPA CA")

field(CALC, "aa==''")

field(OOPT, "When Zero")

field(DOPT, "Use OCAL")

field(OCAL, "'Passive'")

field(OUT, "$(P)$(Q):initLastMotor.SCAN CA")

field(FLNK, "$(P)$(Q):lastMotor")

}

# Find the last motor that will be written to. (Ignore motors that

# don't actually exist.) Write that motor's .DMOV PV

record(scalcout, "$(P)$(Q):lastMotor") {

field(CALC, "(f?ff:e?ee:d?dd:c?cc:b?bb:aa)[0,' ']+' CP'")

field(INPA, "$(P)$(Q):dmov.INAV CA")

field(INPB, "$(P)$(Q):dmov.INBV CA")

field(INPC, "$(P)$(Q):dmov.INCV CA")

field(INPD, "$(P)$(Q):dmov.INDV CA")

field(INPE, "$(P)$(Q):dmov.INEV CA")

field(INPF, "$(P)$(Q):dmov.INFV CA")

field(INAA, "$(P)$(Q):dmov.INPA CA")

field(INBB, "$(P)$(Q):dmov.INPB CA")

field(INCC, "$(P)$(Q):dmov.INPC CA")

field(INDD, "$(P)$(Q):dmov.INPD CA")

field(INEE, "$(P)$(Q):dmov.INPE CA")

field(INFF, "$(P)$(Q):dmov.INPF CA")

field(PINI, "RUNNING")

field(OUT, "$(P)$(Q):closeGate.INPA CA")

}

---snip---

Tim Mooney (mooney at anl.gov) (630)252-5417
Beamline Controls Group (www.aps.anl.gov)
Advanced Photon Source, Argonne National Lab

From: Tech-talk <tech-talk-bounces at aps.anl.gov> on behalf of Johnson, Andrew N. via Tech-talk <tech-talk at aps.anl.gov>
Sent: Thursday, March 5, 2020 12:58 PM
To: Benjamin Franksen <benjamin.franksen at helmholtz-berlin.de>
Cc: EPICS tech-talk <tech-talk at aps.anl.gov>
Subject: Re: CA output links not working with PINI=YES?

Hi Ben,

On Mar 5, 2020, at 12:16 PM, Benjamin Franksen via Tech-talk <tech-talk at aps.anl.gov> wrote:

What we want to do here is write a string to an input link field once at
init time. Link fields can be written to only via CA, which is why we
have to use a CA link.

Do you have to wait until after iocInit to set the value of that input link field? If you could do it beforehand you could load a separate .db file that just sets the link field of that record. You can also use the IOC’s ‘dbpf’ command to write to a link field in your startup script, and the length of that string isn’t limited to 40 characters any more.

Christoph’s original example doesn’t show him writing to a link field, and I’m still a little confused exactly what you’re trying to do. Given the actual complexity of what you’re trying to do (as against the apparent simplicity that you’re wanting) I suspect using a sequence program might be simpler, but more detail of the actual problem might allow us to find a simpler solution.

- Andrew

Complexity comes for free, Simplicity you have to work for.

References:: CA output links not working with PINI=YES? Christoph Schroeder via Tech-talk; Re: CA output links not working with PINI=YES? J. Lewis Muir via Tech-talk; Re: CA output links not working with PINI=YES? Christoph Schroeder via Tech-talk; Re: CA output links not working with PINI=YES? J. Lewis Muir via Tech-talk; Re: CA output links not working with PINI=YES? Ralph Lange via Tech-talk; Re: CA output links not working with PINI=YES? Benjamin Franksen via Tech-talk; Re: CA output links not working with PINI=YES? Johnson, Andrew N. via Tech-talk

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ANJ, 05 Mar 2020

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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System