A four-mode model for efficient fault-tolerant mixed-criticality systems

Mixed-criticality systems (MCS) integrate components from different levels of criticality onto the same platform. MCS, like all other electronic systems, are susceptible to transient faults. These systems must mitigate the effects of faults and provide recovery mechanisms when faults occur. In this paper, we consider the problem of designing and scheduling certifiable fault-tolerant mixed-criticality systems. To address certification and transient faults, two-mode models must treat any single overrun or fault as a combination of the two, reserving time for the re-execution of tasks with extended execution time. We therefore propose a new four-mode model that addresses fault and execution time overrun with separate modes. This model, combined with the selective continuation of low-criticality tasks, improves the quality of service (QoS) to these tasks while providing the same guarantee to high-criticality tasks. Experimental results show that QoS improvements of up to 42.9% can be achieved by the new model. Furthermore, we show how the model and its schedulability analysis can be calibrated to realistic failures rates to achieve even more efficient designs.