Reconfiguration Control Networks for FPGA-based TMR systems with modular error recovery

Field-Programmable Gate Arrays (FPGAs) provide ideal platforms for meeting the computational requirements of future space-based processing systems. However, FPGAs are susceptible to radiation-induced Single Event Upsets (SEUs). Techniques for dynamically reconfiguring corrupted modules of Triple Modular Redundant(TMR) components are well known. However, most of these techniques utilize resources that are themselves susceptible to SEUs to transfer reconfiguration requests from the TMR voters to a central reconfiguration controller. This paper evaluates the impact of these Reconfiguration Control Networks (RCNs) on the system's reliability and performance. We provide an overview of RCNs reported in the literature and compare them in terms of dependability, scalability and performance. Most importantly, we compare the performance of soft networks with that of a hard network that utilizes the Internal Configuration Access Port(ICAP) available in advanced Xilinx devices to periodically read the TMR voter states. We have implemented our designs on a Xilinx Artix-7 FPGA to assess the resulting resource utilization and performance as well as to evaluate their soft error vulnerability using analytical and fault injection techniques. Results show that, of the RCN topologies studied, the ICAP-based approach is the most reliable despite having the highest network latency. We also conclude that a module-based recovery approach is less reliable than scrubbing unless the RCN is implemented with redundancy and repaired when it suffers from configuration memory errors.