Exploiting Application Tolerance for Functional Safety

As the use of safety critical systems is becoming more prevalent, there is a need to reduce the implementation overhead required to provide safety. The conventional design of such systems does not consider application behaviours, thereby resulting in a pessimistic design where the safety provided is often not required during large periods of the application execution. In this paper, we analyse the different phases of an application during its overall execution life cycle, together with the embedded threads to perform specific operations, and propose a new methodology for protection of the safety critical application threads. We show the benefits of this method and the ability to build lower cost systems which are functionally safe using the flexibility which is embedded inside the application itself. Two new application based protection schemes, based on altering the application execution parameters (e.g. control loop frequency) and redundant execution of selective threads, are proposed. For these experiments, we have used commercial off the shelf components without any hardware functional safety features and implemented safety measures by augmenting the application software. Experiments on Electric Vehicle Traction (EVT) and On-Board Charger (OBC) applications indicate overall MIPS savings between 70% to 95%. These results indicate that a careful design of the application can itself be the first step to protect the integrated circuits which drive them.