PALS: Physically Asynchronous Logically Synchronous Systems
Lui Sha, Abdullah Al-Nayeem, Mu Sun, José Meseguer, Peter Csaba Ölveczky · Illinois Digital Environment for Access to Learning and Scholarship (University of Illinois at Urbana-Champaign) · 2009
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