Experimental Physics and
Industrial Control System

Luedeke Andreas <[email protected]> · Wed, 13 Jun 2007 03:13:57 +0200

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: [email protected]
[mailto:[email protected]] On Behalf Of Mathias Steiner

Sent: Tuesday, June 12, 2007 6:00 PM

To: [email protected]

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
[email protected], http://people.web.psi.ch/luedeke

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System