Specification-Guided Automated Debugging of CPS Models

Abstract

Simulink/Stateflow is the de facto tool for developing software for safety-critical real-time cyber-physical systems (CPSs). In Simulink, the model of a CPS is captured in a block diagram-based language, the model is simulated using the associated simulators and then the software code is generated automatically for the embedded controller. The presence of a bug in the Simulink model may lead to catastrophic failure during the execution of the system developed based on the model. Unlike in application software, finding bugs in Simulink models is challenging due to the hybrid nature of the model. We present an automated debugging methodology of a CPS model captured in Simulink. Our methodology has two main components-bug localization and model repair. For bug localization, we capture the requirements of the system in signal temporal logic (STL) and employ the runtime monitoring technique to generate a trace that violates the specification. The violating trace is used to identify the internal signals that have the potential to contribute to the violation. For precise bug localization by narrowing down the offending signals, we employ a matrix decomposition technique to find the signals contributing to the bug accurately. Our bug localization technique is precise enough to enable us to repair the model. If the bug is due to an inappropriate value for a model parameter, we employ a parameter tuning method to find a value for the parameter that repairs the model automatically. We carry out numerous case studies on Simulink models obtained from different sources and demonstrate that our automated debugging technology can fix the bugs in the Simulink models effectively.