PALS: Physically Asynchronous Logically Synchronous Systems

In networked cyber physical systems real time global computations, e.g., the supervisory control of a flight control system, require consistent views, consistent actions and synchronized state transitions across network nodes in real time. This paper presents a real time logical synchrony protocol, Physically Asynchronous Logically Synchronous (PALS), to support real time global computation. Under the PALS protocol, engineers design and verify applications as if all the distributed state machines were driven by a single global clock. The PALS protocol is optimal in the sense that 1) the bound on the periods of the real time global computation, such as the supervisory controller, is the shortest possible, and 2) the message overhead in achieving logical synchrony is minimal. Acknowledgement. Steven P. Miller and Darren Cofer have collaborated with us closely in this work. Min Young Nam, Peter Feiler and Dionisio de Niz have helped us greatly in AADL related challenges. Xiaokang Qiu and Artur Boronat contributed to the translation of AADL to Maude. This work is sponsored by Rockwell Collins Inc., the Office of Naval Research , the National Science Foundation, Lockheed Martin Corporation, the Research Council of Norway, and the Software Engineering Institute.