Software Implemented Detection and Recovery of Soft Errors in a Brake-by-Wire System

This paper presents an experimental study of the impact of soft errors in a prototype brake-by-wire system. To emulate the effects of soft errors, we injected single bit-flips into "live" data in the architected state of a MPC565 microcontroller. We first describe the results of an error injection campaign with a brake-by-wire controller in which hardware exceptions are the only means for error detection. In this campaign, 30% of the injected errors passed undetected and caused the controller to produce erroneous outputs to the brake actuator. Of these, 15% resulted in critical failures. An analysis showed that a majority of the critical failures were caused by errors affecting either the stack pointer or the controller\´s integrator. Hence, we designed two software implemented error handling mechanisms that protect the stack pointer and the integrator state, inducing an overhead of 4% in data and 8% in speed. A second error injection campaign showed that these mechanisms reduced the proportion of critical failures one order of magnitude, from 4.6% to 0.4% of the injected soft errors.