Expanded Version of a Paper from the Sixth Working Conference on Dependable Computing for Critical Applications, Systematic Formal Veriication for Fault-tolerant Time-triggered Algorithms

Many critical real-time applications are implemented as time-triggered systems. We present a systematic way to derive a time-triggered implementation from a fault-tolerant algorithm speciied as a functional program. It is relatively easy to formally and mechanically verify correctness and fault-tolerance properties of algorithms expressed in this latter form. The functional program is next transformed into an untimed synchronous system, and then to a time-triggered implementation. The second step is independent of the algorithm concerned and we prove its correctness; the proof has also been formalized and mechanically checked with the PVS veriication system. This approach provides a methodology that can ease the formal speciication and assurance of critical fault-tolerant systems.