Higher-Order Concurrency for Microcontrollers
This addresses the problem of programming complexity and safety for developers working with microcontrollers, offering a novel approach to concurrency management.
The paper tackles the challenge of unsafe and error-prone concurrent programming on microcontrollers by introducing SenseVM, a virtual machine that provides a higher-order concurrency model based on message-passing, resulting in safer, more composable, and easier-to-maintain code for microcontroller applications.
Programming microcontrollers involves low-level interfacing with hardware and peripherals that are concurrent and reactive. Such programs are typically written in a mixture of C and assembly using concurrent language extensions (like $\texttt{FreeRTOS tasks}$ and $\texttt{semaphores}$), resulting in unsafe, callback-driven, error-prone and difficult-to-maintain code. We address this challenge by introducing $\texttt{SenseVM}$ - a bytecode-interpreted virtual machine that provides a message-passing based $\textit{higher-order concurrency}$ model, originally introduced by Reppy, for microcontroller programming. This model treats synchronous operations as first-class values (called $\texttt{Events}$) akin to the treatment of first-class functions in functional languages. This primarily allows the programmer to compose and tailor their own concurrency abstractions and, additionally, abstracts away unsafe memory operations, common in shared-memory concurrency models, thereby making microcontroller programs safer, composable and easier-to-maintain. Our VM is made portable via a low-level $\textit{bridge}$ interface, built atop the embedded OS - Zephyr. The bridge is implemented by all drivers and designed such that programming in response to a software message or a hardware interrupt remains uniform and indistinguishable. In this paper we demonstrate the features of our VM through an example, written in a Caml-like functional language, running on the $\texttt{nRF52840}$ and $\texttt{STM32F4}$ microcontrollers.