Readback of output variables after iocInit

[redpiramide]

With the current available operation modes, it is possible to exclusively read or write a variable, but there is no support for readback of output variables.

In my use case it is possible that setpoints in the plc get changed manually by a local touch panel, the internal logic or by an opc-ua connection to another plc. The changed setpoints should synchronize back to epics to keep consistency.

To not affect the current operation modes, adding a new mode called RW or to add info(asyn:READBACK, "1") to the record definition may be an option. These records are included in the cyclic SumRead but also allow writing them on request.

See the discussion on the EPICS Tech Talk for Reference:
https://epics.anl.gov/tech-talk/2024/msg00522.php

[Synthetica9]

We're having the same issue, similar with #7

[exzombie]

Thank you for the feedback. I'll take a look at the first opportunity. As noted in the linked discussion, there's a chance that this issue can be more easily solved than #7 and would be sufficient as a workaround for #7 in cases where a short window of UDF after initialization is acceptable.

[redpiramide]

Please take a look at my fork. I have managed to get the readback, but still testing edge cases. I can also open a pull request.