Experimental Physics and
Industrial Control System

Ben Franksen via Tech-talk <tech-talk at aps.anl.gov> · Tue, 30 Mar 2021 21:39:38 +0200

Am 30.03.21 um 19:25 schrieb Johnson, Andrew N. via Tech-talk:
> On Mar 30, 2021, at 11:22 AM, William Layne
> <william.casey.layne at gmail.com> wrote:
>> Unsure if this is still relevant, but I remember there being talk
>> about trying to get channel filters working on put operations. Do
>> you know if that's still being discussed, or even possible? If it
>> is, it could possibly solve this question in the future.
> 
> There is no support inside the EPICS 7.0.5 IOC at the moment for
> running channel filters on puts, and I’m not sure how easy it will be
> to let filters modify an existing array field instead of just
> overwriting it with a new value (which is what the existing put API
> implements).
> 
> Another complexity that I see is agreeing on the semantics of what it
> should mean to run commands like these:
> 
> $ caput ‘array1.[4]' 100 $ caput -a ‘array2.[2:3]' 5 1 2 3 4 5

In my implementation I opted for truncating requests that exceed the
target field's (current) array bounds. This was the simplest thing to do
and the most conservative.

> If array1 holds doubles and starts out empty, would the first command
> set elements 0 through 3 to NaN values, or to zeros? Presumably the
> second command would leave the first 2 elements of array2 alone,
> replace elements 2 and 3 with the values 1 and 2, then insert the
> values 3 4 5 after element 3. Unfortunately implementing these might
> be tricky without breaking the support for circular buffers that the
> array field API currently provides.

Another good reason for request truncation. I agree that in the end we
want to have a way to increase the array length, too, but I am happy to
leave that for a future extension ;-)

Ben
-- 
I would rather have questions that cannot be answered, than answers that
cannot be questioned.  -- Richard Feynman

Experimental Physics and Industrial Control System

Experimental Physics and
Industrial Control System