Applying input/output control of asynchronous sequential machines to dual ring counters

Corrective control can compensate the stable-state behavior of asynchronous sequential machines without involving redesign of the inner logic of the machine. In this paper, we apply the corrective control scheme to a space-borne dual ring counter subject to Single Event Upset (SEU) faults. By virtue of hardware redundancy lying in the dual ring counter, we design a corrective controller that tolerates any SEU fault that causes unauthorized state transitions. Since the output of the counter is unavailable to the controller, input/output control methodology is required for realizing fault diagnosis and tolerance. As a case study, we implement the proposed controller and a 4-bit dual ring counter in VHDL code, and conduct an experiment on the procedure of fault tolerance under a synthetic fault scenario.