Dynamic scheduling of voter checks in FPGA-based TMR systems

SRAM-based Field-Programmable Gate Arrays (FPGAs) are susceptible to radiation-induced Single Event Upsets (SEUs). Techniques for partially reconfiguring corrupted modules of Triple Modular Redundant (TMR) FPGA-based designs have been described in the literature. Most of these techniques require some form of network-on-chip for aggregating voter error messages from the system's TMR components to a central reconfiguration controller in order to trigger the partial reconfiguration of modules when they become faulty. The frequency at which TMR components fail in the system depends on their soft-error vulnerability. However, most error recovery techniques adopt a static voter error checking schedule, which leads to delays in checking TMR components with high failure probability. In this paper we propose a Voter Scheduling Engine (VSE) for dynamically prioritizing and managing TMR voter checks so as to minimize the error detection time in the system and to thereby maximize the system's reliability. Software and hardware implementations of the VSE are proposed. Moreover, we have implemented the classic static voter checking schedule and the VSE on a real TMR system and evaluated the reliabilities of both approaches for varying radiation environments. Results demonstrate that the likelihood of system failure can be decreased by up to 50% when the VSE, rather than static voter checking, is incorporated into the TMR system.