Experimental Physics and
Industrial Control System

Kay-Uwe Kasemir <[email protected]> · Thu, 20 Oct 2005 09:57:29 -0400

Yep. But a new ca feature might be "send me all commands that this

aliased pv understands", which would include the fields of the

device and strings it supports. I guess this would also be defined

in the alias table.

As for 'commands' and how to recognize them:
TANGO, ACS distinguish between commands and properties, or even
commands, static properties and attributes that change at runtime.

Our records have fields, and some fields are
- static properties like INP with VME card/slot number.
  Configured by the application engineer,
  shouldn't change unless the hardware gets reconfigured.
- attributes that update on their own. Read-only.
  Example: AI.VAL when read from some device.
- attributes that get changed at runtime and should
  be preserved in case of reboots.
  Examples include VAL fields of records that hold setpoints.
  Those could be AO.VAL, but also AI.VAL of a soft channel.
  The latter might be a misuse of AI, but it's currently
  possible.
  Fields like the alarm limits are often static,
  but sometimes they are adjusted at runtime and
  thus in this second category.
- Commands
  Most BO.VAL and MBBO.VAL fields are what other systems would
  call commands.
  The motor record has many command fields: move to new position,
  jog, run.

The crux is that our records are too flexible.
In a subroutine records, the inputs could be static
or runtime-adjustable. AI.VAL can be command or readback.
Either the fields must be specialized, e.g. prohibiting
write access to AI.VAL,
and a subroutine record with separate 'config'
and 'runtime' inputs,
so that this "field character" is defined once in the dbd file,
or the db files need additional options to specify
it case by case.
Keeping that information separate on a directory server
is of course an option, but also difficult to keep
in sync with the db files.

-Kay

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System