On the role of the power supply as an entry for common cause faults—An experimental analysis

The principle of duplication and comparison has proven very efficient for error detection in processor cores, since it can be applied as a generic solution for making virtually any type of core fail safe. A weakness of this approach, however, is the potential for common cause faults: Faults affecting both cores in the same way will escape detection. Shared resources and signals are especially prone to such effects. In practice the efforts for providing a redundant power source are often prohibitive, thus rendering the power supply such a shared resource. While a complete failure of the supply voltage can be relatively easily accommodated in a fail safe system, short pulses can have subtle consequences and are therefore much more dangerous. In this paper we will perform an experimental study of the potential of such power supply induced faults to create common cause effects. For this purpose we first study their effects on the operation of a processor core. In particular we will show that, when applied with the most adverse parameters, they tend to cause timing violations in the critical path. In two instances of the same core there is therefore a non-negligible risk of common cause effects. We will quantitatively assess this risk through fault injection experiments into an FPGA based dual core design.