Beyond cross-section: Spatio-temporal reliability analysis

A computational system employed in safety-critical applications typically has reliability as a primary concern. Thus, the designer focuses on minimizing the device radiation-sensitive area, often leading to performance degradation. In this article, we present a mathematical model to evaluate system reliability in spatial (i.e., radiation-sensitive area) and temporal (i.e., performance) terms and prove that minimizing radiation-sensitive area does not necessarily maximize application reliability. To support our claim, we present an empirical counterexample where application reliability is improved even if the radiation-sensitive area of the device is increased. An extensive radiation test campaign using a 28nm commercial-off-the-shelf ARM-based SoC was conducted, and experimental results demonstrate that, while executing the considered application at military aircraft altitude, the probability of executing a two-year mission workload without failures is increased by 5.85% if L1 caches are enabled (thus increasing the radiation-sensitive area) when compared to no cache level being enabled. However, if both L1 and L2 caches are enabled, the probability is decreased by 31.59%.