Neutron Beam Evaluation of Probabilistic Data Structure-based Online Checkers

High-criticality applications are vulnerable to Single Event Effects (SEEs) and require highly reliable and customizable microprocessors. Online checkers have been used to detect security and reliability issues in such systems. Popular hardware redundancy techniques such as Triple Modular Redundancy (TMR) and Dual Modular Redundancy (DMR) provide a high error coverage at the cost of substantial redundancy; therefore, there is an interest in introducing lightweight checkers that could offer the same detection ability as DMR with a much lower overhead. A possible implementation of these online checkers can be based on Probabilistic Data Structure (PDS) such as the Bloom Filter (BF). They are a form of information redundancy and an excellent complement to Single Error Correction Double Error Detection (SECDED) codes because they allow for detecting higher-order upsets. In this work, we integrate an online checker into the open-source RISC-V core NEORV32 and deploy it on a flash-based FPGA. This paper presents the evaluation of the online checker's performance conducted under a neutron beam. The neutron beam experiments demonstrate that the real-life error rates of such structures are comparably worse than the initial simulation would indicate and that other factors can impact their performance.