Energy scheduling for task execution on intermittently-powered devices

Abstract

Intermittently-powered embedded devices (IPDs) are getting wide-spread attention these days. However, running periodic real-time tasks on these devices remains a challenging problem due to the lack of support for data freshness guarantees, timekeeping, and schedulability analysis. Especially, while many sensing tasks require long atomic operations for data acquisition from sensors, most prior work on IPDs assumes compute-only workloads and disregards such sensor operations. In this paper, we present a new energy scheduling scheme to execute periodic real-time tasks with atomic sensing operations. Our scheme keeps track of time and ensures the periodic execution of sensing tasks while efficiently utilizing intermittent power sources. We provide schedulability analysis to determine if a task is schedulable in a given charging setup, and extend this idea for scheduling multiple tasks. As a proof-of-concept, we design a custom programmable RFID tag device, called R'tag, and demonstrate the effectiveness of our proposed techniques in a realistic sensing application. We compare the baseline approach and the proposed scheme in both simulation and real platforms. Experimental results show that the proposed method outperforms the baseline approach in terms of task scheduling, timekeeping, and periodic sensing.