Experimental Physics and
Industrial Control System

Ben Franksen <[email protected]> · Sun, 12 Sep 2010 16:23:36 +0200

On Sonntag, 12. September 2010, Xu, Chengcheng wrote:
> I am trying to test out the EPICS record's new DBE property.

You mean the new CA event type called DBE_PROPERTY?

To summarize: this nice new feature is not yet fully implemented for all 
record types; also, camonitor misses an option to specify the request 
type to make this useful. I tried to add it but it doesn't work.

> We are 
> assuming when the release note states "support subscriptions that get
> events whenever a property of the PV changes."

Note that event types concern properties of PVs as CA sees them. CA has 
no notion of records or fields.

> Does it mean if the meta data i.e value of ioc:example:LOLO 

You mean ioc:example.LOLO?
                    ^
> changes 
> and we were using probe or camonitor to monitor the ioc:example pv,
> it will change the value of LOLO since LOLO is a property of the pv.

It depends on whether the record support code of the record type in 
question has been updated to send events when its LOLO field has 
changed. The CA server depends on the record support to notify it of 
such events.

As the release notes state, the only record types that have been changed 
to send DBE_PROPERTY events are mbbi and mbbo. So you'll probably have 
no luck with LOLO & co, as these are used in analog type records 
(ai,ao,calc,...). Of course you could hack these record supports (or 
some of them) to add this feature.

> We are also interested in knowing how to use camonitor to display the
> meta data of a pv?  

Looking at 'camonitor -h' I see no option for specifying the DBR type, 
so it seems that --apart from timestamp and status/severity-- 
properties are not supported yet. This is in contrast to caget which 
has the -d option, so you could say

  caget -d DBR_GR_DOUBLE ...

> If we camonitor ioc:example, how can we monitor 
> the meta datas without doing camonitor ioc:example ioc:example.LOLO

A work-around could be to set up a

  camonitor -mp ...

to get only the DBE_PROPERTY events, and then arrange to do a caget with 
appropriate DBR type each time camonitor reports an event. You might 
need to scan the camonitor output for newlines (signifying an event). 
This is messy and very inefficient, as caget will open and close a 
channel each time camonitor reports an event.

The better solution is to hack a -d option into camonitor. I tried this 
with the Perl version camonitor.pl (attached). This was a quick cut & 
paste job, and for reasons I cannot determine it does not work as I 
expected: the request type gets reduced to DBR_TIME_DOUBLE:

ben@sarun[1]: ~/tmp > ./camonitor.pl -dDBR_GR_DOUBLE -mp benHost:ai1
benHost:ai1
    Native data type: DBR_DOUBLE
    Request type:     DBR_TIME_DOUBLE
    Element count:    1
    Value:            4
    Timestamp:        2010-08-12 16:09:27.717296
    Status:           LOW
    Severity:         MINOR

(Same result with DBR_CTRL_DOUBLE). I suppose this has to do with either 
CA itself or the Perl CA bindings. Probably Andrew or Jeff can shed 
some light upon the issue...

Cheers
Ben

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System