EMBEDDED  OPERTATING  SYSTEMS

While an Operating System, or RTOS, isn't necessary to write software for the AVR, there may be times when it is desirable. Below, are some links for free or open source operating systems / kernels for the AVR. Note that this may not be a complete list.

Femto OS

The Femto OS is a very concise portable real time - preemptive operating system (RTOS) for embedded microcontrollers with minimal ram and flash.

AvrX

AvrX is a Real-Time Multitasking Kernel.

EtherNut - Nut/OS

Ethernut is an Open Source Hardware and Software Project for building Embedded Ethernet Devices. It contains Nut/OS which is an intentionally simple RTOS for the ATmega128, which provides a minimum of services to run Nut/Net, the TCP/IP stack.

FreeRTOS

FreeRTOS is a portable, open source, mini Real Time Scheduler (or mini RTOS kernel).

TinyOS

TinyOS is a component-based runtime environment designed to provide support for deeply embedded systems which require concurrency intensive operations while constrained by minimal hardware resources.

Contiki

Contiki is an Internet-enabled operating system and desktop environment for a number of smallish systems.

XMK - eXtreme Minimal Kernel

XMK is a preemptive multitasking scheduler/kernel for 8bit microcontrollers. Its goal is to provide a bare bones RTOS with a small enough footprint (RAM+ROM) to run on 8bit microcontrollers.

pico OS

pico OS is a highly configurable and very fast real time operating system (RTOS). It targets a wide range of architectures, from very small 8 bit processors and microcontrollers up to very huge platforms. An AVR port is available.

uSmartX

uSmartX is a non-preemptive, multitasking, priority based RTOS. It features mechanisms for inter-task communication and basic task and time control functions.

Super Simple Tasker (SST)

This is an implementation of a lightweight scheduler so called "Super Simple Tasker" - SST. The idea is taken from the Robert Ward's article - "Practical Real-Time Techniques" http://www.quantum-leaps.com/resources/Ward03.pdf. The SST allows to significantly reduce needs for precious RAM and ROM and still allows to keep a real time characteristic of the scheduler (e.g. tasks prioritization and preemption).

ChibiOS/RT

ChibiOS/RT is a compact and fast RTOS designed for embedded applications. It offers threads, mutexes, semaphores, messages, events, timers, flexible I/O with timeout capability.

Here are some links to free or open source components that may be useful.

uIP - TCP/IP Stack for Embedded Microcontrollers

uIP is an implementation of the TCP/IP protocol stack intended for small 8-bit and 16-bit microcontrollers. It provides the necessary protocols for Internet communication, with a very small code footprint and RAM requirements - the uIP code size is on the order of a few kilobytes and RAM usage is on the order of a few hundred bytes.

Protothreads

Protothreads are extremely lightweight stackless threads designed for severely memory constrained systems such as small embedded systems or sensor network nodes. Protothreads provide linear code execution for event-driven systems implemented in C. Protothreads can be used with or without an underlying operating system.