Modern microcontrollers come with a selection of clock sources that have widely differing frequencies and power consumptions. For applications whose workloads vary over time, dynamically changing the clock can provide significant energy savings. The varying constraints of embedded hardware environments and the complex interactions of multiprogrammed systems makes this approach burdensome to do in application logic. Power Clocks orchestrates energy optimizing clock management in the kernel, obviating the need for application involvement while still achieving acceptable performance for typical workloads. This poster describes Power Clocks's design and presents preliminary results.

We describe Tethys, an energy-harvesting wireless water flow sensor that can monitor water use at a per-fixture level with the intention of associating water use with specific individuals. Tethys was motivated by recent efforts at Stanford University to reduce water use due to the California drought. Understanding how the university population uses water at per-person level can greatly influence policies and conservation approaches. Tethys uses Bluetooth Smart to both identify individuals as well as asynchronously upload data to the cloud for later analysis. We describe two challenges encountered in deploying Tethys: energy harvesting design and the mechanical considerations for high-pressure water at high temperatures.