NvMR: non-volatile memory renaming for intermittent computing

Intermittent systems on energy-harvesting devices have to frequently back up data because of an unreliable energy supply to make forward progress. These devices come with non-volatile memories like Flash/FRAM on board that are used to back up the system state. However, quite paradoxically, writing to a non-volatile memory consumes a lot of energy that makes backups expensive. Idem-potency violations inherent to intermittent programs are major contributors to the problem, as they render system state inconsistent and force backups to occur even when plenty of energy is available. In this work, we first characterize the complex persist dependencies that are unique to intermittent computing. Based on these insights, we propose NvMR, an intermittent architecture that eliminates idempotency violations in the program by renaming non-volatile memory addresses. This can reduce the number of backups to their theoretical minimum and decouple the decision of when to perform backups from the memory access constraints imposed by the program. Our evaluations show that compared to a state-of-the-art intermittent architecture, NvMR can save about 20% energy on average when running common embedded applications.