EMC: Energy-Aware Morphable Cache Design for Non-Volatile Processors

Wearable, implantable and Internet of Things devices are attracting increasing attention from both research and industry fields. Energy harvesting is a promising alternative of battery to power these embedded systems. However, the intrinsic instability of energy harvesting systems leads to potential frequent power interruptions. In traditional volatile processor, all the status will be lost at power failures and the program needs to re-start after power resumes. In order to survive the power failures and enable accumulative execution, non-volatile processor (NVP) is proposed to back up volatile information before power depletion and recover the system status after power resumes. Non-volatile memory (NVM) is typically attached for cache and main memory backup. There are researches working on optimization of the backup. However, little of them involve multiple level cell (MLC) NVM. In this work, we first discuss the benefit of applying MLC NVM for cache backup and the architecture of morphable hybrid cache, and then propose a three-stage energy-aware cache management strategy to improve the system performance and energy utilization while guaranteeing successful backups. Backup-aware cache replacement policies are also developed for backup optimization. Evaluation shows that the proposed EMC scheme can achieve 10.6 percent performance improvement and simultaneous 25.2 percent energy reduction when compared with the single level cell (SLC) based hybrid cache.