Exploiting Same Tag Bits to Improve the Reliability of the Cache Memories

Abstract

With the trend of increasing transient error rate, it is becoming important to prevent transient errors and provide a correction mechanism for hardware circuits, especially for SRAM cache memories. Caches are the largest structures in current microprocessors and, hence, are most vulnerable to the transient errors. Tag bits in cache memories are also exposed to transient errors but a few efforts have been made to reduce their vulnerability. In this paper, we propose to exploit prevalent same tag bits to improve error protection capability of the tag bits in the caches. When data are fetched from the main memory, it is checked if adjacent cache lines have the same tag bits as those of the data fetched. This same tag bit information is stored in the caches as extra bits to be used later. When an error is detected in the tag bits, the same tag bit information is used to recover from the error in the tag bits. The proposed scheme has small area, energy, and performance overheads with error protection coverage of 97.9% on average. Even with large working sets and various cache sizes, our scheme shows protection coverage of higher than 95% on average.