Re: ASLO / AOFF scaling for ai and ao record

[Tim Mooney <mooney@aps.anl.gov>]

Stefan Heim wrote:
> Tim,
>
> On Freitag, 13. Juli 2007, you wrote:
>   
> > Stefan Heim wrote:
> >     
> > > In the streamdevice protocol file I have (among others)
> > >
> > > getX {
> > >         out "Joe Crds ?";
> > >         in "Joe Crds %f %*f %*f %*f %*f %*f %*f ";
> > > }
> > >
> > > setX {
> > >         out "Joe AxisAbs 1 %(VAL)f";
> > >         in "Joe started";
> > > }
> > > [...]
> > >       
> > I think you are *telling* the streamDevice to ignore ASLO and AOFF, by
> > using the
> > format "%(VAL)f".
> >     
>
> That's indeed the case. It's a feature, not a bug ;-) If I use %f instead 
> of %(VAL)f, I get the desired ASLO/AOFF scaling with streamdevice and an ao 
> record.
>
>   
> > As I read the doc, it would do what you want if you 
> > used the
> > format "%f".  According to streamDevice/doc/ao.html, the streamDevice
> > would, in this case, perform the calculation
> >
> >     |OUTPUT_VALUE = (OVAL-AOFF)/ASLO
> >
> > without converting to integer.  (I.e., the streamDevice would grab the
> > required
> > field values, and perform the calculation independently of the record.)
> >     
>
> Can't believe this has slipped through my attention! Stupid mistake, thank you 
> for getting me back on track.
>
> On a academic basis I still wonder whether to give the responsibility to 
> honour ASLO/AOFF to the device support is a good idea. Aren't ASLO/AOFF 
> supposed to be a property of _any_ ao record, regardless what device support 
> it might reside on?
>
> Thanks again,
> -Stefan
>   

Yes, and your record is using these fields to calculate a value for 
RVAL.  Unfortunately,
RVAL isn't useful in your application because it's integer-valued.  So 
streamDevice is
just doing what all device support is permitted to do, which is to use 
information from
the record to craft a value that a device will be able to understand.  
It would be bad if,
for example, streamDevice were to use AOFF as some kind of address, and 
ASLO as a
place to store the device's serial number.  That would be weird.

--
Tim Mooney (mooney@aps.anl.gov) (630)252-5417
Beamline Controls & Data Acquisition Group (www.aps.anl.gov/aod/bcda)
Advanced Photon Source, Argonne National Lab