Q uick R ecall

Abstract

Transiently Powered Computers (TPCs) are a new class of batteryless embedded systems that depend solely on energy harvested from external sources for performing computations. Enabling long-running computations on TPCs is a major challenge due to the highly intermittent nature of the power supply (often bursts of < 100ms), resulting in frequent system reboots. Prior work seeks to address this issue by frequently checkpointing system state in flash memory, preserving it across power cycles. However, this involves a substantial overhead due to the high erase/write times of flash memory. This article proposes the use of Ferroelectric RAM (FRAM), an emerging nonvolatile memory technology that combines the benefits of SRAM and flash, to seamlessly enable long-running computations in TPCs. We propose a lightweight, in-situ checkpointing technique for TPCs using FRAM that consumes only 30 nJ while decreasing the time taken for saving and restoring a checkpoint to only 21.06μ s , which is over two orders of magnitude lower than the corresponding overhead using flash. We have implemented and evaluated our technique, Q uick R ecall , using the TI MSP430FR5739 FRAM-enabled microcontroller. Experimental results show that our highly-efficient checkpointing translate to significant speedup (1.25x - 8.4x) in program execution time and reduction (∼3x) in application-level energy consumption.