Towards Certifiable Software-Implemented Hardware Fault Tolerance

Reliability metrics for hardware faults in safety-/mission-critical systems have been historically based solely on hardware failure rates, quantitatively ignoring any effect of the software. Software reliability is usually considered only in terms of bugs/defects, which is a quantity hard to estimate analytically. In this article, we explore the problem of quantifying the impact of software in reliability against Single Event Upsets, highlighting the limits of the current standards that restrict the use of Commercial-Off-The-Shelf components for critical scenarios. We show how to obtain valid software reliability metrics and how this methodology significantly improves reliability estimation compared to hardware-only estimation. The reliability gain is further improved when considering real-time metrics. This analysis is the first step towards a reconciliation between software and hardware reliability and enables the quantification of reliability introduced by Software-Implemented Hardware Fault Tolerance approaches.