Experimental Physics and
Industrial Control System

The thing is, however, that the server side needs to support that.

If you write to a motor record’s VAL field, the caput will indeed wait until the motor moved to the commanded position, maybe tried again if the error was too large etc., and completes once it did its best to reach the commanded position.

If you use stream device to simply write some setpoint to a device, the caput might wait until stream device sent that message out to the device, but not necessarily until the device did anything about that. If the device is a lakeshore temperature controller that’s asked to cool down from 300 to 30 Kelvin, that might take hours. You need database constructs which typically include the “busy” record to create logic that blocks until the device is indeed “done”. For an example see https://github.com/ornl-epics/lakeshore

That way you have a record that truly delays completion until the device reached the commanded state. You can then simply use the put-callback and you’ll know that the device is in the desired state once that put-callback completes.

-Kay