Lightweight IO virtualization on MPU enabled microcontrollers

In the era of the Internet of Things (IoT), millions of devices and embedded platforms based on low-cost and limited resources microcontroller units (MCUs) will be used in continuous operation. Even if over-the-air firmware update is today a common feature, many applications might require not to reboot or to support hardware resource sharing. In such a context stop, update and reboot the platform is unpractical and dynamic loading of new user code is required. This in turn requires mechanisms to protect the MCU hardware resources and the continuously executing system tasks from uncontrolled perturbation caused by new user code being dynamically loaded. In this paper, we present a framework which provides a lightweight virtualization of the IO and platform peripherals and permits the dynamic loading of new user code. The aim of this work is to support critical isolation features typical of virtualization-ready CPUs on low-cost low-power microcontrollers with no MMU (Memory Management Unit), IOMMU or dedicated instruction extensions. Our approach only leverages the Memory Protection Unit (MPU), which is generally available in all ARM Cortex-M3 and Cortex-M4 microcontrollers. Experimental evaluations demonstrate not only the feasibility, but also a satisfactory level of performance of the proposed framework in terms of memory requirements and overhead.