FreeRTOS

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FreeRTOS
Website	http://www.freertos.org/
Company/ developer	Richard Barry & FreeRTOS Team
OS family	Real-time operating systems
Source model	Open source
Latest stable release	5.0.0 / April, 2008
Marketing target	Embedded devices
Supported platforms	ARM, Atmel AVR, AVR32, HCS12, MicroBlaze, MSP430, PIC, Renesas H8/S, x86, 8052
Kernel type	Microkernel
License	Modified GPL
Working state	Current

FreeRTOS is a real-time operating system for embedded devices, being ported to several microcontrollers. It is distributed under a modified version of the GPL. The modification permits users' proprietary code to remain closed source while maintaining the kernel itself as open source, thereby facilitating the use of FreeRTOS in commercial applications.

Supported architectures:

ARM architecture
- ARM7
- ARM9
- ARM Cortex-M3
Atmel AVR
AVR32
HCS12
MicroBlaze
MSP430
PIC microcontroller PIC18, PIC24, dsPIC, PIC32
Renesas H8/S
x86
8052

The download contains prepared configurations and demonstrations for every port, allowing rapid application design.

The FreeRTOS scheduler is designed to be small and simple. It can be configured for both preemptive or cooperative operation.

To make the code readable, easy to port, and maintainable, it is written mostly in C, but there are a few assembler functions included where needed.

From Version 4, FreeRTOS allows an application to use coroutines, as well as tasks. In FreeRTOS, a Coroutine is a lightweight task that uses very little memory.

FreeRTOS is small and simple. The kernel itself is comprised of only three or four C files, depending on whether coroutines are used or not.

The FreeRTOS.org site also contains RTOS tutorials, details of the RTOS design and performance comparison results for various microcontrollers.

FreeRTOS was the first real time kernel to be available for real (production) CORTEX-M3 based microcontrollers.

FreeRTOS has recently spawned a spin off project called SafeRTOS. SafeRTOS is based on the FreeRTOS code base but has been updated, documented, tested and audited to enable its use in IEC 61508 safety related applications.

Another related project is OpenRTOS, which has an identical code base to FreeRTOS but with different licensing. The OpenRTOS license removes all reference to the GPL and its implications. For example, one of the conditions of using FreeRTOS in a commercial product is that the user is made aware of the use of FreeRTOS and the source code must be provided upon request. OpenRTOS doesn't have this requirement.