Why do we need a Sparse Global Time-Base in Dependable Real-time Systems?

Abstract

In many hi-dependability applications (such as a fly-by-wire system) triple-modular redundancy (TMR) is deployed to mask arbitrary failures of any of its constituent components. A TMR system will only work properly if the three replicated channels are synchronized, operate independently and exhibit a deterministic behavior. Determinism requires that two inputs that are presented to the three independent channel at the same instant must be ordered in the same way by all three channels, i.e., simultaneity must be resolved consistently at the system level. In order to resolve this issue of system-wide consistent temporal ordering of events, a global time base of known precision-as established by the IEEE 1588 standard-is of utmost utility. Given such a global time-base of known precision, one can establish a global sparse time model that supports the consistent ordering of events.