Experimental Physics and
Industrial Control System

Andrew Johnson <[email protected]> · Thu, 07 Jul 2005 14:28:54 -0500

Kay-Uwe Kasemir wrote:

Things I had in mind:
- Add a 'maximum' or 'average' to some ai, ao, calc, subroutine, ...
  record instances

> - Make a record post all/some values to a logging facility
>   or circular buffer

Ok, these are the filters I was talking about - the ability to take a

posted value, apply some additional processing and export the result.

- Add a(n additional) forward link to a record

If we take Ralph's (IIRC) suggestion that the FLNK field be an array of

links, you wouldn't need this. I'm not totally convinced about that

yet, but it's one solution; another would be to just use a fanout record

which is exactly what it was designed for...

In case of the max., average, ..., I think it would be really nice
to have this as a field of the record. How else would I access
the current maximum? I'd like to access it via CA, see it in dbpr, ...

By "export the result" above, I mean make it available through CA as

another named view of the record it applies to. Thus if we provided a

general-purpose "maximum" filter you could connect it to say the value

view of your record "fred" and it would then make the running maximum of

"fred.value" available as a "fred.max" (or whatever you named your new

maximum filtered view). The maximum calculation would be performed by

the filter every time the record posts a new value to the underlying view.

The record has no knowledge of the presence of the filter, it doesn't

have to call any hook routines, and the field view doesn't have to know

anything about an extra field, since this isn't one at all. This exact

same approach can be used to implement the circular buffer logging

facility, and using views this could permit clients to specify

parameters to the view - say "give me the history data for just the last

10 seconds."

Actually, I don't use the FLNK, HIGH, SIML, ... fields in most records,
so could they all go and only be added as required?

That's a rather different requirement, the problem is how you would

connect all the little pieces together and execute them at the right

time. I'd like to find some way of making records out of smaller

objects, but I don't think we're anywhere near that yet.

If I can suggest an alternate approach that could provide this

functionality but doesn't involve "adding a field at runtime", would

you accept this instead?

Absopositively. What do you suggest?

Does the above describe an acceptable alternative?

- Andrew
--
Podiabombastic: The tendency to shoot oneself in the foot.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System