Experimental Physics and
Industrial Control System

Jeff Hill <[email protected]> · Fri, 15 Nov 1996 10:12:13 -0700

Hello all,

After some off line discussion about this request for a modification
to the ca client API allowing the record type and name to be queried.
we have come up with the following potential solution.

A new data type could be added to the dbr_XXX types in db_access.h
and a new PV attribute application type could be added to the
gdd self describing data class as follows:

gdd			ca client		EPICS DB subsystem
---			---------		------------------
gddAppTypeClassName	DBR_CLASS_NAME		the record type
gddAppTypeInstanceName	DBR_INSTANCE_NAME	the record name

This would allow an application to directly query an EPICS 
database PV's record name and type. Other subsystems underneath 
of the CA server would of course implement different mappings for 
these attributes.

The PV model present in the ca client API and the database
access API has had some success fostering a tool 
based approach. Currently, we have two types of PVs:
o Analog with limits, units, etc
o Enumerated with strings associated with each state

I suspect that in many cases the users need to know the record name
only because they need to modify PV attributes such as the units
and the limits by poking directly in record specifc fields? If so,
perhaps the immediate need is to provide write access to the 
compound DBR_XXXX types from the ca client API. This will perhaps
avoid changes in application level code when the record type
changes for a particular record instance in the database.

Any comments?

Jeff

-- 
______________________________________________________________________
Jeffrey O. Hill                 Internet        [email protected]
LANL MS H820                    Voice           505 665 1831
Los Alamos, NM 87545 USA        FAX             505 665 5107

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System