Leveraging Weakly-hard Constraints for Improving System Fault Tolerance with Functional and Timing Guarantees

Many safety-critical real-time systems operate under harsh environment and are subject to soft errors caused by transient or intermittent faults. It is critical and yet often very challenging to apply fault tolerance techniques in these systems, due to their resource limitations and stringent constraints on timing and functionality. In this work, we leverage the concept of weakly-hard constraints, which allows task deadline misses in a bounded manner, to improve system's capability to accommodate fault tolerance techniques while ensuring timing and functional correctness. In particular, we 1) quantitatively measure control cost under different deadline hit/miss scenarios and identify weak-hard constraints that guarantee control stability, 2) employ typical worst-case analysis (TWCA) to bound the number of deadline misses and approximate system control cost, 3) develop an event-based simulation method to check the task execution pattern and evaluate system control cost for any given solution and 4) develop a meta-heuristic algorithm that consists of heuristic methods and a simulated annealing procedure to explore the design space. Our experiments on an industrial case study and a set of synthetic examples demonstrate the effectiveness of our approach.Comment: ICCAD 202

A Generic Coq Proof of Typical Worst-Case Analysis

International audienceThis paper presents a generic proof of Typical Worst-Case Analysis (TWCA), an analysis technique for weakly-hard real-time uniprocessor systems. TWCA was originally introduced for systems with fixed priority preemptive (FPP) schedulers and has since been extended to fixed-priority nonpreemptive (FPNP) and earliest-deadline-first (EDF) schedulers. Our generic analysis is based on an abstract model that characterizes the exact properties needed to make TWCA applicable to any system model. Our results are formalized and checked using the Coq proof assistant along with the Prosa schedulability analysis library. Our experience with formalizing real-time systems analyses shows that this is not only a way to increase confidence in our claimed results: The discipline required to obtain machine checked proofs helps understanding the exact assumptions required by a given analysis, its key intermediate steps and how this analysis can be generalized

Weakly hard schedulability analysis for fixed priority scheduling of periodic real-time tasks

The hard deadline model is very popular in real-time research, but is representative or applicable to a small number of systems. Many applications, including control systems, are capable of tolerating occasional deadline misses, but are seriously compromised by a repeating pattern of late terminations. The weakly hard real-time model tries to capture these requirements by analyzing the conditions that guarantee that a maximum number of deadlines can be possibly missed in any set of consecutive activations. We provide a new weakly hard schedulability analysis method that applies to constrained-deadline periodic real-time systems scheduled with fixed priority and without knowledge of the task activation offsets. The analysis is based on a Mixed Integer Linear Programming (MILP) problem formulation; it is very general and can be adapted to include the consideration of resource sharing and activation jitter. A set of experiments conducted on an automotive engine control application and randomly generated tasksets show the applicability and accuracy of the proposed technique