Networks of ultra-low-power nodes capable of sensing, computation, and wireless communication have applications in medicine, science, industrial automation, and security. Over the past few years, deployments of wireless sensor networks (WSNs) have utilized nodes based on off-the-shelf general purpose microcontrollers. Reducing power consumption requires the development of Systemon-chip (SoC) implementations that must provide both energy efficiency and adequate performance to meet the demands of the long deployment lifetimes and bursts of computation that characterize WSN applications. This work takes a holistic approach and, thus, studies all layers of the design space, from the applications and architecture, to process technology and circuits. This paper introduces the emerging application space of wireless sensor networks and describes the motivation and need for a custom system architecture. The proposed design fully embraces the accelerator-based computing paradigm, including acc...