Fault-tolerant clock synchronization for embedded distributed multi-cluster systems

When time-triggered (TT) systems are to be deployed for large embedded real-time (RT) control systems in cars and airplanes, one way to overcome bandwidth limitations and achieve complexity reduction is the organization in clusters of strongly interacting computing nodes with well-defined interfaces. In this case, clock synchronization of different cluster times supports meaningful exchange of time-related data between clusters and allows coordinated control. This paper addresses fault-tolerant clock synchronization of clusters for TT systems that are already internally synchronized. By addressing systematic and stochastic errors of cluster times differently, the influence of systematic errors is eliminated and the quality of synchronization only depends on stochastic errors. Since systematic errors of cluster times are at least an order of magnitude larger than stochastic errors for typical RT embedded control systems, the presented algorithm achieves a significant improvement to known synchronization algorithms. An implementation of the proposed clock synchronization algorithm on top of the Time-Triggered Architecture and experiments show that synchronization is achieved with accuracy values of less than one microsecond.