Re: Basic Question regarding input links

[Luedeke Andreas <andreas.luedeke@psi.ch>]

Mark Rivers wrote:

> > The reason I'm asking is that in my application, only the 
> > channel access 
> > link causes "answr" to process, the database link doesn't, and we 
> > couldn't agree on what was supposed to happen.
> >    
>
> That is what is supposed to happen.  If you want a record to process
> when its input changes then you must set the link to CP.
>
> PP is what you set output links to if you want it to process the record
> that the output is linked to.
>
> Mark
>
>  
Of course you can use PP on input links, too:
it causes the record that the link points to to process before the data 
is read from the link.

In your example:
if "b.VAL" changes then the record "answr" processes and this in turn 
causes record "a" to process,
before "a.VAL" is read to "answr.B" and "answr.VAL" is calculated.

For further information read the "Record Reference Manual", Chapter 
"1.3. Passive Scanning",
e.g. at
http://www.aps.anl.gov/epics/EpicsDocumentation/AppDevManuals/RecordRef/Recordref-1.html

Cheers
Andreas

> > -----Original Message-----
> > From: tech-talk-bounces@aps.anl.gov 
> > [mailto:tech-talk-bounces@aps.anl.gov] On Behalf Of Mathias Steiner
> > Sent: Tuesday, June 12, 2007 6:00 PM
> > To: tech-talk@aps.anl.gov
> > Subject: Basic Question regarding input links
> >
> > Learned Friends,
> >
> > I have what I believe to be a very basic EPICS question.
> > I'm new to ioc programming, so bear with me, please.
> >
> > Let "a" and "b" be analog input records, passive, initialized to 1.
> > On the same ioc as those two, define
> >
> > record(calc, "answr")
> > {
> >   ...
> >   field(INPA, "a.VAL PP NMS")
> >   field(INPB, "b.VAL CP NMS")
> >   field(CALC, "A+B")
> >   ...
> > }
> >
> > As the ioc starts up, the value of "answr" is 2, as expected.
> >
> > My question is this:
> > When "a" is set to another value, does "answr" process?
> >
> > Also, when "b" is set to a different value, does "answr" process?
> >
> > In other words, does a change in the linked record lead to 
> > processing of 
> > the linking record, and does it do so for both database links and 
> > channel access links?
> >
> > The reason I'm asking is that in my application, only the 
> > channel access 
> > link causes "answr" to process, the database link doesn't, and we 
> > couldn't agree on what was supposed to happen.
> >
> > Cheers, and Thanks in advance,
> > -Mathias
> >
> >    
>
>  


--
Dr. Andreas Luedeke, SLS Operations Manager, Tel:+41-56-3104002
Andreas.Luedeke@psi.ch, http://people.web.psi.ch/luedeke