Re: synchronizing the value of a read/write record

[Torsten Bögershausen via Tech-talk <tech-talk@aps.anl.gov>]

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