QUICKRECALL: A Low Overhead HW/SW Approach for Enabling Computations across Power Cycles in Transiently Powered Computers

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 paper proposes the use of FRAM, an emerging non-volatile 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 decreases the time taken for saving and restoring a checkpoint to only 12.6μs, which is over two orders of magnitude lower than the corresponding overhead using flash. We have implemented and evaluated our technique, QUICKRECALL, using the TI MSP430FR5739 FRAM-enabled microcontroller. Experimental results show that our highly-efficient checkpointing translates to a significant speedup (1.4x - 4.5x) in program execution time.