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

Subject: Re: EPICS alarming on VAL != X
From: Benjamin Franksen <[email protected]>
To: <[email protected]>
Date: Fri, 25 Jul 2014 14:05:21 +0200
On Thursday 24 July 2014 11:27:24 Andrew Johnson wrote:
> On 07/24/2014 04:47 AM, Benjamin Franksen wrote:
> > On Thursday 24 July 2014 11:15:56 Dirk Zimoch wrote:
> >> On 21.07.2014 12:41, Benjamin Franksen wrote:
> >>> Why don't you just set DRVL=DRVH=<the desired value>.
> >>>
> >>      /* check drive limits */
> >>      if (prec->drvh > prec->drvl) {
> >>
> >>          if (value > prec->drvh)
> >>
> >>              value = prec->drvh;
> >>
> >>          else if (value < prec->drvl)
> >>
> >>              value = prec->drvl;
> >>
> >>      }
> >>
> >> DRVL=DRVH => no check at all!
> >
> > Strange. Not intuitive to me. And contrary to the docs.
>
> That check predates the CVS history of the aoRecord.c file (1995). It
> makes perfect sense to me, there has to be a way to disable the
> clipping behaviour,

Hm, yes, that makes sense.

> and the assumption is that you would only create
> ao records for things that you want to be able to actually change.

In general, yes, but there are exceptions. I have used ao or ai records
to hold physical constants as parameters for a calculation. It would be
nice if I could tell the database to fix the value and not even allow a
db or ca put to change them. (One solution could be a simple record type
for such parameters. Maybe I'll write one when I have some leisure...)

> If
> you want to stop changes for a while, disable record processing using
> SDIS & DISV.

I don't think this will prevent the VAL from changing e.g. due to put
operations, or does it?

> > This is from the
> > RRM
> > (https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14_Analog_Outpu
> > t#Desired_Output_Parameters):
> >
> > """
> > The VAL field's value is forced to be within the limits specified in
> > the fields DRVH and DRVL, which are configured by the designer:
> >
> > DRVL<=VAL<=DRVH
> >
> > Note: If nothing is entered for DRVH and DRVL, the output value will
> > never change.
> > """
>
> Wiki page fixed to document existing code.

Thanks.
Ben
--
"Make it so they have to reboot after every typo." ― Scott Adams


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Replies:
Re: EPICS alarming on VAL != X Dirk Zimoch
Re: EPICS alarming on VAL != X Andrew Johnson
References:
EPICS alarming on VAL != X Jameson Graef Rollins
Re: EPICS alarming on VAL != X Benjamin Franksen
Re: EPICS alarming on VAL != X Andrew Johnson

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