Software-Based Triple Modular Redundancy with Fault-Tolerant Replicated Voters

New computing-intensive applications such as assisted or highly automated driving are rapidly expanding the domain of safety-critical embedded systems, driven by the vision of the driverless car. This development makes it necessary to use high performance multi-core systems which are commercially available and provide more parallelism in terms of redundant execution units, however, at the cost of being less reliable. With the continuous down-scaling of semiconductor technology, computing hardware exhibits an increasing vulnerability against random hardware faults. Since these high-performance controller provide less or no hardware redundancy to ensure a safe execution of the application, software-only fault tolerance approaches are under current investigation. Our Scalable Software Support for Dependable Embedded Systems (S3DES) approach achieves fault tolerance by utilizing software-based triple modular redundancy for computational and optimized arithmetic encoded voter processes to ensure fault detection and error handling on application level. In S3DES voters are replicated to allow the compensation of voting failures. However, new challenges with regard to error propagation and multiple voting result outputs are introduced by this extension. We describe how mutual voter monitoring and threshold value checks could be used to establish a hierarchy among the replicated voters without re-introducing a reliability bottleneck in the sense of a single point of failure and resolve the aforementioned challenges.