Ultra-low-power sensor nodes featuring a virtual runtime environment

The widespread diffusion of wireless sensor networks and wearable devices, together with the emergence of energy harvesting techniques, has motivated the development of ultra-low-power micro controller units (MCUs) which are highly energy efficient in active mode and provide a wide range of sleep states to be possibly exploited to save power during idle periods. In spite of their energy efficiency, state-of-the-art MCUs exhibit 16-bit RISC architectures clocked at up to tens of MHz and equipped with at least 16kbytes of main memory and 64kbytes of flash. This makes them suitable to run a virtual machine, bringing the benefits of a virtual runtime environment to power-constrained embedded systems. Virtual machines, however, impair the effectiveness of dynamic power management since they are seen as always-active processes by the scheduler of the operating system. This paper presents a power-manageable open-source embedded virtual environment based on a modified version of the Darjeeling VM running on top of Contiki OS. The proposed architecture has been implemented and tested on Texas Instruments´ MSP430 MCUs which have been used as a testbed for the characterization of the power consumption and transitions cost of each power state.