High-level synthesis of triple modular redundant FPGA circuits with energy efficient error recovery mechanisms
There is a growing interest in deploying commercial SRAM-based Field Programmable Gate Array (FPGA) circuits in space due to their low cost, reconfigurability, high logic capacity and rich I/O interfaces. However, their configuration memory (CM) is vulnerable to ionising radiation which raises the need for effective fault-tolerant design techniques. This thesis provides the following contributions to mitigate the negative effects of soft errors in SRAM FPGA circuits. Triple Modular Redundancy (TMR) with periodic CM scrubbing or Module-based CM error recovery (MER) are popular techniques for mitigating soft errors in FPGA circuits. However, this thesis shows that MER does not recover CM soft errors in logic instantiated outside the reconfigurable regions of TMR modules. To address this limitation, a hybrid error recovery mechanism, namely FMER, is proposed. FMER uses selective periodic scrubbing and MER to recover CM soft errors inside and outside the reconfigurable regions of TMR modules, respectively. Experimental results indicate that TMR circuits with FMER achieve higher dependability with less energy consumption than those using periodic scrubbing or MER alone. An imperative component of MER and FMER is the reconfiguration control network (RCN) that transfers the minority reports of TMR components, i.e., which, if any, TMR module needs recovery, to the FPGA's reconfiguration controller (RC). Although several reliable RCs have been proposed, a study of reliable RCNs has not been previously reported. This thesis fills this research gap, by proposing a technique that transfers the circuit's minority reports to the RC via the configuration-layer of the FPGA. This reduces the resource utilisation of the RCN and therefore its failure rate. Results show that the proposed RCN achieves higher reliability than alternative RCN architectures reported in the literature. The last contribution of this thesis is a high-level synthesis (HLS) tool, namely TLegUp, developed within the LegUp HLS framework. TLegUp triplicates Xilinx 7-series FPGA circuits during HLS rather than during the register-transfer level pre- or post-synthesis flow stage, as existing computer-aided design tools do. Results show that TLegUp can generate non-partitioned TMR circuits with 500x less soft error sensitivity than non-triplicated functional equivalent baseline circuits, while utilising 3-4x more resources and having 11% lower frequency.
TMR, FPGA, HLS, SEU, Reliability models, Energy consumption, Productivity, Fault-tolerance, TLegUp, Partial reconfiguration, Space applications, Error recovery, Essential bits, Xilinx FPGAs, Markov chain
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