A Analysis and Scheduling of a Battery-Less Mixed-Criticality System with Energy Uncertainty

We consider a battery-less real-time embedded system equipped with an energy harvester. It scavenges energy from an environmental resource according to some stochastic patterns. Because of technical constraints, the harvester device first buffers the harvested energy into a reservoir; then, at regular time intervals, the buffered energy is transferred to a super-capacitor. The success of jobs is threatened in case of energy shortage which might be due to lack of harvested energy, losses originated from the super-capacitor self-discharge, as well as power consumption of executed tasks. The periodic real-time tasks of the system follow a dual-criticality model. In addition, each task has a minimum required success-ratio that needs to be satisfied in steady-state. We analytically evaluate the behavior of such a system in terms of its energyrelated success-ratio for a given schedule. Based on these results, we propose a scheduling algorithm that satisfies both, the temporal and success-ratio constraints of the jobs, while respecting task criticalities and corresponding system modes. The accuracy of the analytical method as well as its dependence on the numerical computations and other model assumptions are extensively discussed through comparison with simulation results. Also, the efficacy of the proposed scheduling algorithm is studied through comparison to some existing non-mixedand mixed-criticality scheduling algorithms.