EPICS Home EPICS Controls Argonne National Laboratory

Experimental Physics and
Industrial Control System

Format page
for printing


Search Tech-talk
1994  1995  1996  1997  1998  1999  2000  2001  2002  2003  2004  2005  2006  2007  2008  2009  2010  2011  2012  2013  2014  2015  2016  2017  2018  2019  2020  2021  <2022>  2023  2024  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  2018  2019  2020  2021  <2022>  2023  2024 
<== Date ==> <== Thread ==>
Subject: Re: Change PVA structure dynamically during IOC operation
From: "Alnajjar, Dawood via Tech-talk" <tech-talk at aps.anl.gov>
To: "Kasemir, Kay" <kasemirk at ornl.gov>, "tech-talk at aps.anl.gov" <tech-talk at aps.anl.gov>
Date: Wed, 28 Sep 2022 18:29:04 +0000
Hi Kay,

Thank you for the prompt reply.

Would it make sense to you to dynamically remove the PV (rpvxs::server::Server::emovePV) and then add it again (pvxs::server::Server::addPV)? Would that produce unpredictable results?

Dawood
From: Kasemir, Kay <kasemirk at ornl.gov>
Sent: Wednesday, September 28, 2022 11:25 AM
To: tech-talk at aps.anl.gov <tech-talk at aps.anl.gov>; Alnajjar, Dawood <dnajjar at slac.stanford.edu>
Subject: Re: Change PVA structure dynamically during IOC operation
 
> I need to change a PVA structure dynamically during IOC operation. Looking at pvxs::ioc::server, I do not see an update function that allows that. Does anyone know if this is possible?

I don't think that's possible.

If you check the protocol documentation, https://github.com/epics-base/pvAccessCPP/wiki/protocol, you'll find that the overall structure information is exchanged once when a client connects. From then on, only a compact bitmap that indicates what changed is sent, plus the modified values.
To change the structure, the protocol would have to send the complete new structure.
Arrays can change the number of elements, but the overall structure stays the same because the protocol was optimized for this.

Replies:
Re: Change PVA structure dynamically during IOC operation Kasemir, Kay via Tech-talk
References:
Change PVA structure dynamically during IOC operation Alnajjar, Dawood via Tech-talk
Re: Change PVA structure dynamically during IOC operation Kasemir, Kay via Tech-talk
Navigate by Date:
Prev: Re: Change PVA structure dynamically during IOC operation Kasemir, Kay via Tech-talk
Next: Re: Change PVA structure dynamically during IOC operation Andrew Johnson via Tech-talk
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  2018  2019  2020  2021  <2022>  2023  2024 
Navigate by Thread:
Prev: Re: Change PVA structure dynamically during IOC operation Kasemir, Kay via Tech-talk
Next: Re: Change PVA structure dynamically during IOC operation Kasemir, Kay via Tech-talk
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  2018  2019  2020  2021  <2022>  2023  2024 
ANJ, 28 Sep 2022 Valid HTML 4.01! · Home · News · About · Base · Modules · Extensions · Distributions · Download ·
· Search · EPICS V4 · IRMIS · Talk · Bugs · Documents · Links · Licensing ·