Shoulder Angel: An Open Platform for Reprogramming Wayward Wireless Sensors.

Software bugs are a critical threat to the deployability and maintainability of low-power wireless sensors, resulting in excess power consumption, hardware misconfigurations, incorrect data, and shortened device lifetimes. Worse, these errors can prevent wireless reprogramming, resulting in longer delays and costly human interventions. This letter describes shoulder angel—an ultra-low-power, low-cost, open hardware and software platform that ensures users can always recover and reprogram wireless sensors, in spite of software errors. Shoulder angel uses a physically separate coprocessor to monitor a device’s power consumption and other behaviors, while keeping the device in a reprogrammable state. Our results show that shoulder angel is able to recover from otherwise fatal software errors while incurring an energy overhead of only 7 $ {\\mu }\\text{W}$ .