Remote measurement of local oscillator drifts in FlexRay networks

Distributed systems, especially time-triggered ones, are implementing clock synchronization algorithms to provide and maintain a common view of time among the different nodes. Such architectures heavily rely on the nodes´ local oscillators to remain within given accuracy bounds. However, measuring the oscillator frequencies (e.g., for maintenance or diagnosis) is usually difficult to perform since it requires physical access to each single node and may interfere with the running application. Moreover, clock synchronization features tend to mask clock deviations. In this work, we propose a non-intrusive method for remote measurement of the individual oscillator drifts within a distributed system. Our approach is based on a tester that sends carefully aligned messages to stimulate the clock synchronization service and records the resulting bus traffic for an analysis of the nodes´ synchronization behavior. This tester needs access to the communication bus only. We focus our work to FlexRay and validate our approach by experiments.