RIOT is an open-source microcontroller operating system, designed to match the requirements of Internet of Things (IoT) devices and other embedded devices. These requirements include a very low memory footprint (on the order of a few kilobytes), high energy efficiency, real-time capabilities, support for a wide range of low-power hardware, communication stacks for wireless and communication stacks for wired networks.
RIOT provides threading, multiple network stacks, and utilities which include cryptographic libraries, data structures (bloom filters, hash tables, priority queues), a shell and more. RIOT supports a wide range of microcontroller architectures, radio drivers, sensors, and configurations for entire platforms, e.g. Atmel SAM R21 Xplained Pro, Zolertia Z1, STM32 Discovery Boards etc. (see the list of supported boards. Across all supported hardware (32-bit, 16-bit, and 8-bit platforms), RIOT provides a consistent API and enables C and C++ application programming, with multithreading, IPC, system timers, mutexes etc.
A good high-level overview can be found in the article RIOT: An Open Source Operating System for Low-End Embedded Devices in the IoT (IEEE Internet of Things Journal, December 2018).
RIOT powers the Internet of Things like Linux powers the Internet. RIOT is a free, open source operating system developed by a grassroots community gathering companies, academia, and hobbyists, distributed all around the world.
RIOT supports most low-power IoT devices, microcontroller architectures (32-bit, 16-bit, 8-bit), and external devices. RIOT aims to implement all relevant open standards supporting an Internet of Things that is connected, secure, durable & privacy-friendly.
The goal of this article is to run a C program bare metal on an ARM Cortex M3. We will go through the assembler code generated from a small program written in C and come up with the prerequisites that must be in place in order for it to run.
NuttX is a real-time operating system (RTOS) with an emphasis on standards compliance and small footprint. Scalable from 8-bit to 32-bit microcontroller environments, the primary governing standards in NuttX are Posix and ANSI standards. Additional standard APIs from Unix and other common RTOS's (such as VxWorks) are adopted for functionality not available under these standards, or for functionality that is not appropriate for deeply-embedded environments (such as fork()).
NuttX was first released in 2007 by Gregory Nutt under the permissive BSD license.