Vulnerability-based Interleaving for Multi-Bit Upset (MBU) protection in modern microprocessors

We present a novel methodology for protecting incore microprocessor memory arrays from Multiple Bit Upsets (MBUs). Recent radiation studies in modern SRAMs demonstrate that up to 55% of Single Event Upsets (SEUs) due to alpha particle or neutron strikes result in MBUs. Towards suppressing these MBUs, methods such as physical interleaving or periodic scrubbing have been successfully applied to caches. However, these methods are not applicable to in-core, high-performance Content-Addressable Memories (CAM) arrays, due to computational complexity, high delay and area overhead, and lack of information redundancy. To this end, we propose a cost-effective method for enhancing in-core memory array resiliency, called Vulnerability-based Interleaving (VBI). VBI physically disperses bit-lines based on their vulnerability factor and applies selective parity to these lines. Thereby, VBI aims to ensure that an MBU will affect at most one critical bit-field, so that the selective parity will detect the error and a subsequent pipeline flush will remove its effects. Experimental results employing simulation of realistic MBU fault models on the instruction queue of the Alpha 21264 microprocessor in a 65nm process, demonstrate that a 30% selective parity protection of VBI-arranged bit-lines reduces vulnerability by 94%.