Experimental Physics and
Industrial Control System

"Johnson, Andrew N. via Tech-talk" <tech-talk at aps.anl.gov> · Fri, 13 Mar 2020 23:05:55 +0000

Hi Ben,

Ralph was talking about the server-side filters that were added to Base in 3.15. Documentation for the filters available in 3.15.7 is available at https://epics.anl.gov/base/R3-15/7-docs/filters.html and the source code for those filters is found on the 3.15 branch in src/std/filters, or for 7.0 under modules/database/src/std/filters. The filter sources have a registrar routine that adds a Channel Filter Plugin by calling chfPluginRegister(); the IOC implementation is inside the dbChannel.c and dbChannel.h parts of the src/ioc/db directory. However as Ralph said there isn’t a way for a filter to modify data that is being written to the IOC yet, so far we only have methods for filtering on reads (similar paths are used for both Get and Monitor operations).

Hope this is enough to get you started.

- Andrew

> On Mar 13, 2020, at 5:48 PM, Ben Franksen via Tech-talk <tech-talk at aps.anl.gov> wrote:
> 
> Hi Ralph
> 
> thanks for your reply.
> 
> Am 06.03.20 um 09:26 schrieb Ralph Lange via Tech-talk:
>> On Thu, 5 Mar 2020 at 19:42, Benjamin Franksen via Tech-talk <
>> tech-talk at aps.anl.gov> wrote:
>> 
>>> Is there an EPICS version where I can write (via link, DB or CA) a
>>> scalar to one specific element (i.e. index) of an array field? I am not
>>> as up to date on EPICS development as I used to be, so perhaps this has
>>> been added and I missed it, perhaps in 7.x (hope dies last...).
>> 
>> Filters on write (that would be the obvious way to do it) have not been
>> implemented yet.
>> Dirk Zimoch added filters for DB links at the last Codeathon, but - as with
>> CA - these are only working for get and monitor; there's nothing (yet) for
>> the write operations.
> 
> Interesting. Could you point me to some place where I can read about
> these developments? It sounds like some progress has indeed been made.
> So with Dirk's additions I can now read a single element from an array
> via DB link?
> 
> BTW, I am a bit confused by your terminology, i.e. don't quite get how
> this is a "filter". ATM my best guess is that this is because it was
> discovered that the same mechanism that was originally designed to allow
> filtering of events turned out to be more general and allow things like
> re-targeting of links?
> 
>> Pull Requests / Merge Proposals are always welcome!
> 
> Where does this link filtering code live? (I mean which file or
> directory in base.)
> 
> Cheers
> Ben
> <pEpkey.asc>

-- 
Complexity comes for free, simplicity you have to work for.

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System