Peripheral and Power Management in Batteryless, Energy-Harvesting Systems

Batteryless, energy-harvesting devices enable deeply embedded sensing and computing deployments without the size, weight, or maintenance constraints of batteries. These devices harvest energy into a small capacitor bank to support short bursts of execution at a time, with power failures in between. Peripheral sensors and radios are essential to batteryless device deployments; they allow a device to sense and report information about its surroundings. However, peripherals trigger concurrent accesses to memory and account for a large percentage of the total device energy budget. The challenge for programmers is a tight coupling emerges between device hardware characteristics and application peformance. A software developer needs to have an understanding of both to write programs that behave as expected. This thesis reduces the burden of integrating peripherals into batteryless applications by managing the shared state between peripherals and the primary microcontroller. 

We first address the problem of shared memory between peripheral triggered interrupts and a program’s main loop by defining a programming model that prevents concurrency control violations due to power failures. Peripheral operations also affect the state of the system by changing the total operating power, e.g. by turning a sensor on or off. We demonstrate that peripheral mismanagement leads to a new class of energy bugs that cause hard-stop failures and waste energy in batteryless systems. To correct these bugs, we model changes in peripheral power over a program’s execution. However, peripheral power does not fully capture the hardware state of the device. A device’s power system characteristics also determine when it is safe to access a peripheral. Using a lightweight model of the power system, we correct existing scheduling algorithms for batteryless devices to accommodate high-current peripherals on volume-constrained systems. Finally, we apply the lessons learned throughout this thesis to develop the failure-aware hardware and software support for a miniature batteryless satellite. The ease with which we integrate failure-agnostic peripheral subsystems demonstrates the value of power and peripheral management in batteryless devices.