Experimental Physics and
Industrial Control System

[email protected] (Ned Arnold) · Tue, 11 Feb 1997 08:39:48 -0600

> 
> While we're on the subject of changing record definitions... Has it occurred to
> anybody else how much nicer life would be if the calc record had an output
> link?
> 
> 					Eric Bjorklund
> 					LANSCE Operations
> 

Prior to EPICS release 3.13, we used a "WAIT" record here at ANL (which is
included in base and documented in the Record Reference Manual) that was
very much like a calc record with the following added features :

    - an output link that was "conditionally" executed. Options included
      Execute Output Link ...
          - every time the record processed 
          - when val changes
          - when val = 0
          - when val != 0
          - when val transitions to 0
          - when val transitions to non-zero

    - Input and output links were not real PV_LINKs, they were text strings
      that contained PV names that a caClient (running in the database) would
      connect to. This made the input links "dynamic", i.e. they could be
      changed on the fly without rebooting. The library that supported this
      is included in base as recDynLink (3.12.2) or recWaitCa (3.12.1.x). It
      also made it possible to process the record when an input value changed,
      which was very desirable.

    - There is also a programmable delay from when the record processes
      to when the output link was executed.

    - Optionally, a software EVENT could be posted instead of (or in addition
      to) the output link being executed.

Starting with R3.13, ALL PV_LINKs are "reassignable" on the fly, so much of 
the "novelty" of recDynLink has been incorporated into standard EPICS. In
an attempt to make recDynLink go away some day, a calcAo record was written
in an attempt to merge the capabilities of the WAIT record and the CALC record.

Currently, the calcAo record is not in R3.13 base, it is in our SHARE directory.
It has the above mentioned features of the WAIT record PLUS

	- a second calculation field used to <optionally> output a
          separately calculated value to the output link. The first calculation
          determines whether the output link will be processed, the second
          derives the output data to use.

        - Input links are standard PV_LINKs, compatible with currently
          defined CALC records, but also are reassignable and can cause the
          record to process when the input value changes (CP attribute of 
          the PV_LINK).

        - Adds the option of what to do with the output link if the alarm
          severity is INVALID (like the AO record).

What we would like feedback on is this ...

Should the calcAo record ...

	- be added to base in R3.13  ?
        - replace the CALC record in R3.13 ? (to minimize "similar" records)
        - be made available to only those that politely ask for it ?

	Ned

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System