Experimental Physics and Industrial Control System
|
Hi Andrew,
I haven't given other links any thought.
For DOL on output records, however, one could store the constant
link value, which is evaluated on record init in a record private
structure and pick it up from there when processing.
Ideally this private value should be updated, if the value of the
constant link is changed. Mhhh?
- rolf -
On 6/14/2013 8:30 AM, Andrew Johnson wrote:
Hi Rolf,
On 2013-06-14 Rolf Keitel wrote:
I am setting DOL
to the desired constant value and OMSL=closed_loop and
everything seems to work as desired.
When I do a caput to one of these ao records, however, the
record
outputs from this moment the value received from the caput and
ignores
the DOL value.
This seems counter-intuitive to me. I had expected that in
closed_loop
mode, the VAL field would be *always*
obtained from the DOL link.
Does anyone remember what the rationale is for treating a
constant link
differently from a db or ca link?
Constant links are only ever read once, at record initialization
time, and
this is true for all link fields of all record types. I assume
this was done
to avoid having to call strtod() or its equivalent every time the
IOC reads
the link, which could be a significant drag on performance for
something like
a CALC or SEQ record which have many links that are often
constants. A link
field that has not been set is currently a constant link too.
There is an opportunity to reconsider this design in some work I'm
doing for
3.15/3.16 and v4 (link support), but I would still want to avoid
converting
the value from its string every time the link gets read. The
ability to
specify string and array constants also comes to mind as
desirable, but don't
hold your breath waiting.
- Andrew
--
+-------------------------------------------------------+
| Rolf Keitel, Ph.D. Tel: (604) 222-7453 |
| TRIUMF |
| Vancouver, B.C., Canada |
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