Experimental Physics and
Industrial Control System

"J. Frederick Bartlett ([email protected])" <[email protected]> · Fri, 19 Apr 2002 17:03:59 CDT

  I have encountered a problem with the use of EPICS monitors. I have
a generic record, which I wrote several years ago, that is a general
purpose interface to a MIL/STD1553B bus controller -- much in the
spirit of the generic VME record written by Mark Rivers.  It is used
primarily for low-level diagnostic operations on the bus.  Recently, I
have added monitor support to the record so that our diagnostic
routines, which operate as EPICS CA clients, could execute more
efficiently and with lower network traffic.

  I added the appropriate code to my record to call db_post_events for
the VAL field and for the STATUS field.  The latter contains the
detailed, bit-encoded driver status for the last operation performed
by the record instance.

  To my considerable surprise, I found that the CA client received
monitor events for the STATUS field but not for the VAL field.
Suitable sprinkling of logMsg calls in the record module have
convinced me that db_post_events is being called correctly, i.e. with
the correct arguments, for both fields.  The VAL field has one unusual
feature: the SPC_DBADDR property; and I suspect that this may be the
source of my problem.

  I have looked at the waveform record, which is similar to my record
in that the VAL field is used to access an array of values rather than
a single value.  The waveform record places a monitor on the BPTR
field rather than the VAL field. However, since the BPTR field has the
DBF_NOACCESS type, I do not see how a CA client can connect a monitor. 

  So, how should I handle the monitoring of a VAL (or any other) field
that has the SPC_DBADDR property?

						Fritz

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System