ECC-United Cache: Maximizing Efficiency of Error Detection/Correction Codes in Associative Cache Memories

Error Detection/Correction Codes (EDCs/ECCs) are the most conventional approaches to protect on-chip caches against radiation-induced soft errors. The overhead of EDCs/ECCs is a major concern and is of decisive importance when a higher protection capability is required to tolerate multiple adjacent bit errors (burst errors). This article proposes the ECC-United Cache (EUC) architecture to improve the efficiency of EDCs/ECCs in set-associative L1 caches. EUC architecture extends the data protection granularity from a single word to multiple words by exploiting the parallel cache lines access, which is inherently available in the cache. As compared with the conventional architecture, EUC can be configured to provide: 1) the same protection capability with a significantly lower overhead, 2) a significantly higher protection capability with the same number of check bits, or 3) a trade-off between the former two features. Simulation results show that, when configured to minimize the overhead, EUC reduces the number of check bits by 69 and 75 percent in data-cache and instruction-cache, respectively. When configured to maximize the protection capability, EUC provides fourfold higher burst error detection/correction capability. Moreover, EUC is orthogonal to previous protection schemes and they can be redesigned based on the EUC architecture to further improve their efficiency.