Closed-loop determinism for non-deterministic environments: Verification for IEC 61499 logic controllers

Verification of logic controllers can identify errors during the design stage so they can be remedied and prevent some faults from occurring once the system is running. Input order robustness is the property that multiple inputs arriving in a variety of orders, and regardless of the order, produce the same set of outputs and same final state. Verifying this property ensures determinism of the closed-loop system even if the environment is non-deterministic. Because use of the IEC 61499 standard for distributed control is becoming more widespread, we present the application of input order robustness verification to controllers implemented in this formalism. Open issues with IEC 61499 execution semantics are presented and discussed in relation to input order robustness verification.