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FreeRTOS

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FreeRTOS is a real-time operating system kernel[3][4][5] for embedded devices that has been ported to 40 microcontroller platforms. It is distributed under the MIT License.

FreeRTOS
DeveloperAmazon Web Services
Written inC
OS familyReal-time operating systems
Working stateCurrent
Source modelOpen source
Initial release2003; 21 years ago (2003)
Latest release11.1.0[1] / April 22, 2024; 7 months ago (2024-04-22)
Repository
Marketing targetEmbedded systems
Available inEnglish
PlatformsARM (ARM7, ARM9, Cortex-M3, -M4, -M7, -A, -R4), Atmel AVR, AVR32, HCS12, MicroBlaze, Cortus (APS1, APS3, APS3R, APS5, FPF3, FPS6, FPS8), MSP430, PIC, Renesas H8/S, SuperH, RX, x86, 8052, Coldfire, V850, 78K0R, Fujitsu series MB91460, MB96340, Nios II, TMS570, RM4x, Espressif ESP32, RISC-V (e.g. SHAKTI)
Kernel typeReal-Time Microkernel
LicenseMIT[2]
Official websitewww.freertos.org

History

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The FreeRTOS kernel was originally developed by Richard Barry around 2003, and was later developed and maintained by Barry's company, Real Time Engineers Ltd. In 2017, the firm passed stewardship of the FreeRTOS project to Amazon Web Services (AWS). Barry continues to work on FreeRTOS as part of an AWS team.[6] With the transition to Amazon control, subsequent releases of the project also switched licensing from GPL version 2 (with special exceptions for static linking to proprietary code outside the FreeRTOS kernel itself) to MIT.[7]

Implementation

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FreeRTOS is designed to be small and simple. It is mostly written in the C programming language to make it easy to port and maintain. It also comprises a few assembly language functions where needed, mostly in architecture-specific scheduler routines.

Process management

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FreeRTOS provides methods for multiple threads or tasks, mutexes, semaphores and software timers. A tickless mode is provided for low power applications. Thread priorities are supported. FreeRTOS applications can be statically allocated, but objects can also be dynamically allocated with five schemes of memory management (allocation):

  • allocate only;
  • allocate and free with a very simple, fast, algorithm;
  • a more complex but fast allocate and free algorithm with memory coalescence;
  • an alternative to the more complex scheme that includes memory coalescence that allows a heap to be broken across multiple memory areas.
  • and C library allocate and free with some mutual exclusion protection.

RTOSes typically do not have the more advanced features that are found in operating systems like Linux and Microsoft Windows, such as device drivers, advanced memory management, and user accounts. The emphasis is on compactness and speed of execution. FreeRTOS can be thought of as a thread library rather than an operating system, although command line interface and POSIX-like input/output (I/O) abstraction are available.

FreeRTOS implements multiple threads by having the host program call a thread tick method at regular short intervals. The thread tick method switches tasks depending on priority and a round-robin scheduling scheme. The usual interval is 1 to 10 milliseconds (1⁄1000 to 1⁄100 of a second) via an interrupt from a hardware timer, but this interval is often changed to suit a given application.

The software distribution contains prepared configurations and demonstrations for every port and compiler, allowing rapid application design. The project website provides documentation and RTOS tutorials, and details of the RTOS design.

Key features

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  • Book and reference manuals.
  • Small memory size, low overhead, and fast execution.
  • Tick-less option for low power applications.
  • Intended for both hobbyists and professional developers working on commercial products.
  • Scheduler can be configured for both preemptive or cooperative multitasking.
  • Coroutine support (coroutines in FreeRTOS are simple and lightweight tasks with limited use of the call stack)
  • Trace support through generic trace macros. Tools such as Tracealyzer, a commercial tool by FreeRTOS partner Percepio, can thereby record and visualize the runtime behavior of FreeRTOS-based systems for debugging and verification. This includes task scheduling and kernel calls for semaphore and queue operations.

Supported architectures

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Derivations

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Amazon FreeRTOS

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Amazon provides a now deprecated extension of FreeRTOS, this is FreeRTOS with libraries for Internet of things (IoT) support, specifically for Amazon Web Services. Since version 10.0.0 in 2017, Amazon has taken stewardship of the FreeRTOS code, including any updates to the original kernel.[9][10][11]

SAFERTOS

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SAFERTOS was developed as a complementary version of FreeRTOS, with common functions, but designed for safety-critical implementation. FreeRTOS was subject to hazard and operability study (HAZOP), and weaknesses were identified and resolved. The result was put through a full IEC 61508 SIL 3 development lifecycle, the highest level for a software-only component.

SAFERTOS was developed by Wittenstein High Integrity Systems, in partnership with Real Time Engineers Ltd, primary developer[3] of the FreeRTOS project.[12] Both SAFERTOS and FreeRTOS share the same scheduling algorithm, have similar application programming interfaces (APIs), and are otherwise very similar,[13] but they were developed with differing objectives.[14] SAFERTOS was developed solely in the C language to meet requirements for certification to IEC61508.[15]

SAFERTOS can reside solely in the on-chip read-only memory (ROM) of a microcontroller for standards compliance.[16] When implemented in hardware memory, SAFERTOS code can only be used in its original, certified configuration. This means certifying a system needs no retesting of the kernel portion of a design.[17] SAFERTOS is included in the ROM of some Stellaris Microcontrollers[18] from Texas Instruments. SAFERTOS source code does not need to be separately purchased. In this usage scenario, a C header file is used to map SAFERTOS API functions to their location in read-only memory.

OPENRTOS

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OPENRTOS is a commercially licensed version of Amazon FreeRTOS, sold by Wittenstein High Integrity Systems. This product provides support and allows companies to use the Amazon FreeRTOS kernel and libraries without the a:FreeRTOS MIT license.[19][20]

See also

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References

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  1. ^ "FreeFTOS Github Releases". GitHub. 2024-04-22.
  2. ^ "FreeRTOS open source licensing". 2017-12-22.
  3. ^ a b "2011 Embedded Market Study". EE Times. Archived from the original on 2012-04-02.
  4. ^ Kolesnik, Sergey (2013-12-08). "Comparing microcontroller real-time operating systems". A kernel is not an RTOS, but this can be a confusing issue because of the inappropriate naming chosen for some popular kernels, 'freeRTOS' for example.
  5. ^ "Why RTOS and What Is RTOS?". Retrieved 29 August 2014. What is FreeRTOS? … The size constraints, and dedicated end application nature, rarely warrant the use of a full RTOS implementation - or indeed make the use of a full RTOS implementation possible. FreeRTOS therefore provides the core real-time scheduling functions, inter-task communication, timing, and synchronisation primitives only. This means it is more accurately described as a real time kernel, or real time executive. …
  6. ^ "RTOS - Free professionally developed and robust real time operating system for small embedded systems development".
  7. ^ "Update to MIT licensed FreeRTOS V10.0.0".
  8. ^ "Using FreeRTOS on RISC-V Microcontrollers". FreeRTOS. Retrieved 11 September 2019.
  9. ^ "Amazon FreeRTOS". Amazon. Retrieved 28 November 2018.
  10. ^ "FAQ: Amazon FreeRTOS". FreeRTOS. Retrieved 28 November 2018.
  11. ^ "Amazon FreeRTOS is a new OS for IoT". TechCrunch. 29 November 2017. Retrieved 4 December 2018.
  12. ^ "FreeRTOS". Retrieved 8 Aug 2012.
  13. ^ "SmartBotPaper" (PDF). Archived from the original (PDF) on 2012-07-04. Retrieved 8 Aug 2012.
  14. ^ Relationship between FreeRTOS and SAFERTOS
  15. ^ "EETimesSafetyCritical". Retrieved 8 Aug 2012.
  16. ^ "Embedded Systems Design Europe". Archived from the original on 23 October 2012. Retrieved 10 Aug 2012.
  17. ^ "Texas Instruments" (PDF). Archived from the original (PDF) on 4 July 2013. Retrieved 10 Sep 2012.
  18. ^ TI Stellaris Product range
  19. ^ "OPENRTOS". High Integrity Systems. Retrieved 28 November 2018.
  20. ^ "FreeRTOS open source licensing". FreeRTOS. Retrieved 28 November 2018.
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