Enhancing the Success Rate of Primary Version While Guaranteeing Fault-Tolerant Capability for Real-Time Systems

Primary/alternate version technique is a cost-effective means which trades the quality of computation results for promptness to tolerate the software faults. Generally speaking, this method requires that each real-time periodic task has two versions: primary and alternate. The primary version provides a result that is in some sense more desirable, but it may be subject to timing failure due to its complexity. On the contrary, the alternate version simply affords an acceptable service, but it could guarantee the timeliness owing to its simplicity. The kernel algorithm proposed in this paper employs the off-line backwards-RM scheme to pre-allocate time intervals to the alternate version and the on-line RM scheme to dispatch the primary version. Simulation results show that kernel algorithm provides higher success rate of primary version.