Maximize Energy Utilization for Ultra-Low Energy Harvesting Powered Embedded Systems

Energy harvesting systems become increasingly popular as power sources for many embedded systems. However, the harvesting power is often weak and the execution is frequently interrupted. Therefore, embedded systems have to work intermittently. To maintain the execution progress for better energy utilization, embedded systems need to save all execution states and program stacks into the non-volatile memory before each power failure, which is known as checkpointing. Then, embedded system waits until power comes back on again. By then the system can resume previous execution state. Nevertheless, frequent checkpointing incurs extra energy overhead. Besides, the charging efficiency of the storage capacitor reduces as the capacitor is charging up. These problems reduce the energy efficiency, resulting in less program execution progress. To alleviate these problems, this paper proposes three algorithms. First, a priority-based task scheduling (PTS) is proposed to prioritize the execution of tasks which have less checkpointing contents for a lower software overhead. Then, a tentative checkpointing avoidance (TCA) technique is proposed to avoid unnecessary checkpointing for further reduction of software overhead. Finally, a dynamic wake-up strategy (DWS) is proposed to wake up the system at proper voltages where the total hardware and software overheads are minimized. In this way, the system can achieve further energy efficiency improvements. The experiments on a real testbed show that the proposed prioritized algorithms enable the targeted embedded system to be resilient to extremely weak and intermittent power while achieving better energy utilization.