Mitigating Read-disturbance Errors in STT-RAM Caches by Using Data Compression

Due to its high density and close-to-SRAM read latency, spin transfer torque RAM (STT-RAM) is considered one of the most-promising emerging memory technologies for designing large last level caches (LLCs). However, in deep sub-micron region, STT-RAM shows read-disturbance error (RDE) whereby a read operation may modify the stored data value and this presents a severe threat to performance and reliability of STT-RAM caches. In this paper, we present a technique, named SHIELD, to mitigate RDE in STT-RAM LLCs. SHIELD uses data compression to reduce number of read operations from STT-RAM blocks to avoid RDE and also to reduce the number of bits written to cache during both write and restore operations. Experimental results have shown that SHIELD provides significant improvement in performance and energy efficiency. SHIELD consumes smaller energy than two previous RDE-mitigation techniques, namely high-current restore required read (HCRR, also called restore-after-read) and low-current long latency read (LCLL) and even an ideal RDE-free STT-RAM cache.