  This work presents InfiniWolf, a novel multi-sensor smartwatch that can
achieve self-sustainability exploiting thermal and solar energy harvesting,
performing computationally high demanding tasks. The smartwatch embeds both a
System-on-Chip (SoC) with an ARM Cortex-M processor and Bluetooth Low Energy
(BLE) and Mr. Wolf, an open-hardware RISC-V based parallel ultra-low-power
processor that boosts the processing capabilities on board by more than one
order of magnitude, while also increasing energy efficiency. We demonstrate its
functionality based on a sample application scenario performing stress
detection with multi-layer artificial neural networks on a wearable
multi-sensor bracelet. Experimental results show the benefits in terms of
energy efficiency and latency of Mr. Wolf over an ARM Cortex-M4F
micro-controllers and the possibility, under specific assumptions, to be
self-sustainable using thermal and solar energy harvesting while performing up
to 24 stress classifications per minute in indoor conditions.
