VHDL - based Fault Injection with VERIFY

This paper describes a new methodology to inject transient and permanent faults in digital systems. For this purpose, the simulation based fault injector VERIFY (VHDL-based Evaluation of Reliability by Injecting Faults efficientlY) has been developed, which allows fault injection at several abstraction levels of a digital system. The combined approach of injection and analysis of the results enables the system’s engineer to evaluate the reliability of the system as well as the coverage of fault tolerance mechanisms applied to the system. The approach is applied to the DP32-processor, where faults are injected at pin-level, by flipping bits in internal registers and gate-level. The results of this comparison shows, that the time to recover from a fault and the total number of faults which lead to a recovery differ significantly according to the type of fault injection. Whereas in the first 2 μs after fault injection using the bitflip fault model more than 79% of all faults injected were still present in the system, only 4.5% remained in the processor when using a stuck-at fault model at gate-level.