Argonne National Laboratory

Experimental Physics and
Industrial Control System

1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  <2017 Index 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  <2017
<== Date ==> <== Thread ==>

Subject: Re: Question related to PV record
From: "Kasemir, Kay" <kasemirk@ornl.gov>
To: Vandana Yadav <vandanayadav477@gmail.com>, "tech-talk@aps.anl.gov" <tech-talk@aps.anl.gov>
Date: Mon, 6 Mar 2017 14:25:39 +0000
Hello:

>I am facing the problem that if the link is broken or not connected then the last stored values are being displayed in IOC by putting caget and caput commands. >How can i resolve this ? Is there any procedure to clear the last stored value ?

As Mark mentioned, EPICS records are by design keeping the last value.
They don't "clear" it. For one, what would "clear" mean? Set the value to zero? What if zero could also be a valid value? Set the value to NaN? Can't do that with longin, bi, mbbi, mbbiDirect, .. records.
Also, to debug a problem it can be helpful to know the last value we received before experiencing a read error.
Instead, records tend to keep the last known value and add for example a READ alarm with INVALID severity in case of read errors.
Strictly speaking it's not the record but device support which sets the value of the record, so one could implement device support that sets the value to "-1" or "0" or "NaN" in case of errors, but as far as I know most leave the value untouched in case of errors.

Most GUI tools would reflect the alarm state: You see the last known value, but there's for example a purple border around the widget to indicate that we don't really know the current value, it has an INVALID alarm severity.

The 'caget' command will by default not show alarm detail, but when you use 'camonitor' you'll see the alarm.
With 'caget', check 'caget -h' for the various request type options.
Given a numeric record,
   caget -d DBR_STS_DOUBLE YourPVName
will show the value with alarm status & severity.

-Kay


Replies:
Re: Question related to PV record J. Lewis Muir
References:
Question related to PV record Vandana Yadav
RE: Question related to PV record Mark Rivers

Navigate by Date:
Prev: RE: Question related to PV record Mark Rivers
Next: Re: Question related to PV record J. Lewis Muir
Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  <2017
Navigate by Thread:
Prev: RE: Question related to PV record Mark Rivers
Next: Re: Question related to PV record J. Lewis Muir
Index: 1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  <2017
ANJ, 06 Mar 2017 Valid HTML 4.01! · Home · News · About · Base · Modules · Extensions · Distributions · Download ·
· EPICS V4 · IRMIS · Talk · Bugs · Documents · Links · Licensing ·