Experimental Physics and
Industrial Control System

Kay-Uwe Kasemir <[email protected]> · Tue, 05 Jul 2005 14:06:10 -0400

Hi:

On Jul 1, 2005, at 18:48, Benjamin Franksen wrote:

See V4 Database Access -> V4 Design: Assembling Record Support

Thanks for putting it up on the wiki.

What I don't understand is:

How do you get process() to include processInvalidOutput() at the

chosen time?

Is that code manually written?
Or is it generated, invoking all process<fieldname> routines
in the order in which the fields are listed in the DBD file?

So how do you propose to associate the code that belongs to a certain
entension (and implements all this nice dynamic behavior) with the
extra field and the record support?

As shown on the wiki page, you pick the field name, type, parameters
to the code and code itself when defining the record instance:

calc("fred")
{
   ...
   user_field(SMOO,  iocFloat64T, "0.5", smoo_handler)
}

The 'smoo_handler' is located just like device support etc. are
located via the registry.
The user_field_handler interface has an init routine in which
smoo_handler can hook into the record's process().

Pro:
+ I can add fields per record instance as needed.
  I think it's easier for end users to grasp that
  you have AI, AO, CALC records
  plus 'average' and 'max' field that I can add to any of them,
  than to present them with the 3x2=6 custom record types
  BasicAI, MaxAI, AverageAI, AverageAndMaxAI, BasicAO, MaxAO, ...
+ Under vxWorks, I can do so without recompilation:
  ld <smoo_handlerLib.o
  dbLoadDataBase("..../records_that_use_smoo_handler")

Contra:

- For now, I only saw the necessity to provide process()-hooks in 2

places.

  When we need many more, your suggestion of re-writing process() and
  recompiling the whole record is better.
- the user_field_handler::init() can check the user field type,
  the record type etc. at runtime, but then you only see errors
  at runtime.
  With pre-defined records in the dbd file, more of that could
  be handled at compile time.

Thanks,
-Kay

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System