Experimental Physics and
Industrial Control System

Benjamin Franksen <[email protected]> · Thu, 30 Aug 2012 01:32:21 +0200

Am Donnerstag, 30. August 2012, 00:42:48 schrieb Michael Davidsaver:
> On 8/28/2012 1:08 PM, Eric Norum wrote:
> > On Aug 28, 2012, at 9:42 AM, Bruno Seiva Martins
> > <[email protected] <mailto:[email protected]>> wrote:
> >
> > ...
> >
> > The documentation at
> > https://wiki-ext.aps.anl.gov/epics/index.php/RRM_3-14_Analog_Input#specia
> > l_linconv describes this pretty well:
> >
> > special_linconv(precord,after)
> >
> > This routine is called whenever any of the fields LINR, EGUF, EGUL or
> > ROFF is modified. To support linear conversion, EOFF and ESLO must be
> > set accordingly. The record support sets EOFF to EGUL before calling
> > this routine, which is the very common case when RAWL is zero below.
> >
> > A useful formula for calculating EOFF and ESLO is this one:
> >
> > EOFF = (RAWF * EGUL - RAWL * EGUF) / (RAWF - RAWL)
> > ESLO = (EGUF - EGUL) / (RAWF - RAWL)
> >
> > Here, RAWL and RAWF are the lowest resp. highest possible raw value.
> > For instance, a 16 bit bipolar ADC might have RAWL=-0x7fff, RAWF=0x7fff.
>
> Did RAWF and RAWL ever exist in a 3.14 release?
>
> A quick search through VCS history shows that these fields only existed
> briefly between 3.14.0-alpha2 and -beta1 (circa 2001).
>
> It would be nice to have them, then linear conversions would be
> unambiguous defined by fields and we could do without special_linconv().

It's interesting that you ask. When I wrote the above lines I did not suspect
that they had ever been actual fields, once. I used them only as a notational
device, though I agree that it would be much nicer to just let device support
set RAWF and RAWL (as part of init_record); the record support could then
calculate ESLO/EOFF from these and EGUF/EGUL -- and the other way around, too,
e.g. user changes EOFF or ESLO => record support updates EGUF and EGUL.

Is this a change that could be made for 3.15 or is it too disruptive?
--
Ben Franksen
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Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System