Hmm, I don't know about "usual" but I see a couple possibilities.
#1 Add your routine as a separate timed task where it will interrupt the other process to run your task. This occurs at a timed interval you choose.
#2. Add your routine into a new program within the Continuous Task. Remember the ControlLogix uses Tasks then under each Task you have up to 32 programs. Your program would automatically run either before or after their program completes, depending upon the Program Schedule.
#3. Add your routine to their programs and then add logic to specify when your routine should be called.
It would appear to me that choice #2 would be the best way to go as it would not involve changing their logic (choice #3) and would not limit you to only running on a timed interrupt (choice #1).
OG