FreeRTOS

FreeRTOS is a real-time operating system kernel for embedded devices that has been ported to 35 microcontroller platforms. It is distributed under the MIT License.
History
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.
Implementation
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
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 (to 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
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
Altera Nios II
ARM architecture
ARM7
ARM9
ARM Cortex-M
ARM Cortex-A
Atmel
Atmel AVR
AVR32
SAM3, SAM4
SAM7, SAM9
SAMD20, SAML21
Ceva
Ceva-BXx
SensPro
Ceva-XC16
Ceva-XM6
Ceva-Xx
Ceva-XM4
Cortus
APS1
APS3
APS3R
APS5
FPS6
FPS8
Cypress
PSoC
Energy Micro
EFM32
eSi-RISC
eSi-16x0
eSi-32x0
DSP Group
DBMD7
Espressif
ESP8266
ESP32
Fujitsu
FM3
MB91460
MB96340
Freescale
Coldfire V1, V2
HCS12
Kinetis
IBM
PPC404, PPC405
Infineon
TriCore
Infineon XMC4000
Intel
x86
8052
Microchip Technology
PIC18, PIC24, dsPIC
PIC32
Microsemi
SmartFusion
Multiclet
P1
NXP
LPC1000
LPC2000
LPC4300
Renesas
78K0R
RL78
H8/S
RX600
RX200
SuperH
V850
RISC-V
RV32I
RV64I
PULP RI5CY
Silicon Labs
Gecko (ARM Cortex)
STMicroelectronics
STM32
STR7
Texas Instruments
C2000 series (TMS320F28x)
MSP430
Stellaris
Hercules (TMS570LS04 & RM42)
Xilinx
MicroBlaze
Zynq-7000
Derivations
Amazon FreeRTOS
Amazon provides an extension of FreeRTOS, referred to as a: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.
SAFERTOS
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 of the FreeRTOS project. Both SAFERTOS and FreeRTOS share the same scheduling algorithm, have similar application programming interfaces (APIs), and are otherwise very similar, but they were developed with differing objectives. SAFERTOS was developed solely in the C language to meet requirements for certification to IEC61508.
SAFERTOS can reside solely in the on-chip read-only memory (ROM) of a microcontroller for standards compliance. 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. SAFERTOS is included in the ROM of some Stellaris Microcontrollers 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
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.
See also
Embedded operating system
References
External links
Amazon Web Services
ARM operating systems
Embedded operating systems
Free software operating systems
Microkernel-based operating systems
Microkernels
Real-time operating systems