Development and Verification of Dependable Software of Cyber-Physical Systems using Time-aware Computations

Abstract: Wired and wireless networking is becoming a necessary part of industrial control systems’ design and is one of the reasons that required a new cyber-physical approach to modelling. The phenomenon observed in cyber-physical systems (CPS) is a variety of cross-dependencies and influences between physical processes, computational devices and communications, which needs to be taken into account at the design and verification stage. Since most of the systems' functionality nowadays is implemented via software, the ability of software to be agnostic to the mentioned cross-influences is of high importance. This work introduces a concept called time-aware computations (TAC), which, instead of aiming at determinism, that is very expensive in distributed systems, aims at adaptability and robustness. It is based on the event-timestamping mechanism and is intended to let the developer handle each communication delay case individually thus minimizing its impact on functional properties of the automation system. It allows the controller to take into account actual point-to-point delay of the measured sensor readings, and adjust the control reaction accordingly, instead of trying to put the upper bound on it and wait for the maximum possible delay time. In industrial automation, the function block architecture of the IEC 61499 standard is increasingly used for modelling complex  distributed  automation  systems. It is  based  on  the  concepts  of  event-driven  block  diagrams, and originally was created as a new programming paradigm for industrial automation controllers, but as a number of recent studies show, it also  allows (and has been used) for  modelling  of CPS  composed of  physical  processes  combined  with  control and communication.The second major co-contribution of this work is a formal model of IEC 61499-based systems with timestamps that allows for modelling and verification of control logic (and closed-loop models) designed with TAC approach in mind. This would also allow for application of model-driven design methodologies later down the road.Third contribution is a software tool-chain that aims to greatly reduce the engineering work when applying formal verification to the designed systems.The proposed contributions' feasibility and effectiveness are demonstrated on a number of case studies.