Applying adaptive safety analysis techniques [for embedded software]

Current needs for high-reliability reusable software, rapid evolutionary development and verification of innovative software architectures have focused attention on improving techniques for analysing the safety and reliability of embedded software. The work reported in this paper integrates two successful safety analysis techniques which have been used separately on software and hardware into the system engineering process. This process combines SFMECA (software failure modes and effects criticality analysis) and SFTA (software fault tree analysis) in a way that can be readily adapted to a particular project´s evolving system needs. The technique was used on two recent space instruments: the Mars Microprobe Project and the Earth Orbiting System´s Microwave Limb Sounder. The main lessons learned from this experience are discussed: (1) flexible use, (2) a risk-driven rather than sequential approach, (3) “zoom-in/zoom-out” use, (4) SFMECA and SFTA as complementary techniques, (5) preserving traceability, and (6) applicability to fault protection software