Experimental Physics and
Industrial Control System

Dirk Zimoch <[email protected]> · Wed, 25 Mar 2015 17:54:20 +0100

On 25.03.2015 17:21, Andrew Johnson wrote:

On 03/25/2015 10:55 AM, Dirk Zimoch wrote:

On 25.03.2015 04:46, Matt Newville wrote:

Yes, I think this idea of getting the ctrl variables in the connection
callback is a good idea, and will allow more straightforward code  As it
is, a pyepics.PV is already expected to be a "rich" object, even if
sacrificing ultimate performance, and is normally expected to have the
ctrl variables.   So, I think it's reasonable to have this getting of
ctrl variables as the default.    I'll add that.

This is generally a good idea for every ca client. After a reboot,
anything may have changed: Enum strings, limits, units, precision, array
size, even record type (and thus data type).

Recent versions of Base (3.14.11 on) have a CA monitor event type
DBE_PROPERTY which was intended for monitoring changes to metadata like
the ctrl variables. 3.14 IOCs don't send out many property events (and
the PV Gateway doesn't support property subscriptions yet either), but
as 3.15 and later IOCs come in they make the case for using this quite a
bit more compelling. I would encourage CA client developers to read the
tech-talk threads discussing DBE_PROPERTY first though, there are a few
gotchas.

- Andrew

This is a different issue. The problem here was not that IOCs changed

their properties on the fly but after a reboot! Even EPICS 3.13 should

have been able to handle that. But many ca clients are too lazy. That

means the client programmer had not thought about the possibility that

IOCs may actually change during a reboot.

Dirk

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System