Re: medm with epics-base 3.14.6+

[Ralph Lange <Ralph.Lange@bessy.de>]

Hi Emmanuel,

Emmanuel Mayssat wrote:
> I am trying to update my driver to a more recent epics base.
> I assume that if I do so, I need to recompile the epics extensions.
>   
Not necessarily. Depends on your definition of "extensions":

You are right, if you mean "IOC-type" extensions that are (at least 
partly) running on the IOC. Drivers, Auto-Save/Restore, CA put logging - 
that kind of extensions. Everything running on one IOC has to be 
compiled against the same version of EPICS base.

For the "classical" extensions, there is always Channel Access between 
your IOC and the extension. CA works as a big integrator - a 
compatibility layer that allows a wild mix of EPICS base versions on 
IOCs and clients.

There is no need to run all your IOCs with the same version of base. 
There is no need to run all CA clients compiled against the same version 
of base.
This is an important feature: In large operational systems with short 
shutdown phases it would be impossible to upgrade hundreds of IOCs or 
all CA client applications at the same time.

Two obvious exceptions:
You can only avoid running into problems with bugs that have been fixed 
by running recent versions of base (this applies to the IOC aka CA 
server as well as to the client side).
If you plan to use CA features that have been added at some point (e.g. 
large array buffers), you have to make sure that all servers and clients 
using the feature have been compiled against a version of base that 
supports it. (Not necessarily the same version, but a recent enough 
version to support the feature.)

Cheers,
Ralph