Re: synchronizing the value of a read/write record

[Maren Purves via Tech-talk <tech-talk@aps.anl.gov>]

Having done something like this in the  early 2000s after being told
by Bob Dalesio (and a few others) "you 'can't do that", but writing
to a device on a serial line from 2 different sources, it took me a
week to figure out and another week to figure how I did it  years
later.
This did not involve device support, just serial line, and that may
also be the only thing you need - if you get the database and/or SNL
right (no SNL in my case).

I think I can find a db file - working with EPICS 3.13.8 (get me/us
funding to hire a sys-admin I might actually get around to upgrading
EPICS - currently I'm more sys-admn than anything else)

Maren

On Tue, Aug 12, 2025 at 11:32 PM Torsten Bögershausen via Tech-talk
<tech-talk@aps.anl.gov> wrote:
>
> Hej Patrick,
>
> Before answering with a longer answer, I would like to understand
> what "the other source" is.
>
> Is it
> a)
>    The same device,that you are controlling ?
>    May be a device that has a user interface on its own,
>    display, keyboard, touch screen ?
>    Or are the values changed throug a user program,
>    engineering tool, something in that style ?
> b)
>    The new values come from a different device, and are
>    stored in a different record.
>    May be a controll-loop where device1 says that device2
>    (the one you are talking about) "please use this value"
>
> Hope this questions are understandable.
>
>
> On 2025-08-13 02:41, Thomas, Patrick via Tech-talk wrote:
> > Hello,
> >
> > I'm attempting to write device support to handle the scenario where
> > changes to the value of a hardware device can be made from both EPICS
> > and another source. I would like the value of the hardware to be changed
> > if I write a value to the record through channel access, and also to
> > continuously monitor the hardware device for changes made from the other
> > source and update the value of the record to match. One approach I have
> > considered is to use separate output and input records, where the output
> > records write values set from channel access to the hardware and the
> > input records periodically scan the hardware and update their values
> > accordingly. I am wondering however if there is a way to do this with
> > the val field of just an output record. Is there any way to synchronize
> > things so that write requests coming from channel access are always
> > written to the hardware and not overridden by periodic updates from
> > reading the hardware?
> >
> > Thank you,
> > Patrick
> >
>