FreeRTOS

Introduction

FreeRTOS is a market-leading real-time operating system (RTOS) for microcontrollers and small microprocessors. Distributed freely under the MIT open source license, FreeRTOS includes a kernel and a growing set of libraries suitable for use across all industry sectors. FreeRTOS is built with an emphasis on reliability and ease of use.

FreeRTOS SDK supports FreeRTOS on below CPUS

  • ARM R5F

  • TI C75

  • ARM A53 (single core and SMP on all cores)

Features Supported

  • FreeRTOS Kernel 11.1.0

    • Tasks, semaphores, mutex, queues, timers, list, heap, event groups

    • preemptive priority based scheduler

    • static and/or dynamic memory allocation mode

  • FreeRTOS SMP Kernel 11.1.0

    • Tasks, semaphores, mutex, queues, timers, list, heap, event groups

    • preemptive priority based scheduler for multiple cores

    • static and/or dynamic memory allocation mode

  • FreeRTOS+POSIX

    • Limited POSIX API wrappers on top of FreeRTOS APIs

    • Clock, message queue, pthread, pthread cond, pthread mutex, semaphore, timer

  • In order to keep the device drivers agnostic of FreeRTOS or NORTOS, additionally below Driver Porting Layer (DPL) APIs are implemented to call FreeRTOS APIs underneath,

    • Clock, task, semaphore, heap, cache, MPU, debug logs, HW interrupts, HW timers

  • Floating point save/restore with tasks (make sure to call portTASK_USES_FLOATING_POINT() before using floating point operations )

  • M4F ISRs,

    • nested interrupts supported

  • DM_R5F ISRs,

    • IRQ mode,

      • FPU save/restore is supported.

  • MCU_R5 ISRs

    • IRQ mode,

      • nested interrupts supported

  • A53 ISRs,

    • IRQ mode,

      • nested interrupts supported

SysConfig Features

Note

It is strongly recommend to use SysConfig where it is available instead of using direct SW API calls. This will help simplify the SW application and also catch common mistakes early in the development cycle.

SysConfig can be used to configure below modules with FreeRTOS

  • Clock module, to setup system tick timer including the tick duration

  • Debug Log module, to select the console to use for logging as well as enable/disable logging zones

  • MPU ARMv7, to setup different MPU regions for DM_R5F and MCU_R5F CPUs

  • MMU ARMv8, to setup different MMU regions for A53 CPUs and C75 core

  • Address Translate module, to setup address translation regions, needed for DM_R5F and MCU_R5F

  • HW Timer module, to setup HW timer available on the SOC, including enabling timer interrupt and ISR registration

Features Not Supported

  • Co-routines, stream buffer are not enabled and are not compiled by default. Users can add these to the FreeRTOS config and makefile if they want to use these features.

  • Tickless IDLE mode

  • Task level memory protection wrapper

  • FIQ mode,

    • nested interrupts not supported

    • FPU save/restore not supported.

  • DM_R5F ISRs,

    • IRQ mode,

      • nested interrupts is disabled, due to issues in some corner cases.

    • FIQ mode,

      • nested interrupts not supported.

      • FPU save/restore not supported.

  • MCU_R5F ISRs

    • FPU save/restore not supported.

  • A53 ISRs,

    • FPU save/restore not supported.

Important files and directory structure

FreeRTOS source is distributed along with FreeRTOS SDK and given below are some important files and folders related to FreeRTOS.

Folder/Files Description
${SDK_INSTALL_PATH}/source/kernel/
dpl/ APIs to access FreeRTOS features in a OS agnostic way
${SDK_INSTALL_PATH}/source/kernel/freertos
lib/ FreeRTOS library to link against. Linking to the library in this path enables the application to operate in FreeRTOS mode
config/ FreeRTOS and FreeRTOS POSIX configuration header files for different CPUs within a SOC.
FreeRTOS-Kernel/ FreeRTOS Kernel source code. MCU+ SDK simply clones the code from FreeRTOS github and does not modify anything in this folder
FreeRTOS-Kernel-smp/ FreeRTOS Kernel source code for SMP. MCU+ SDK simply clones the code from FreeRTOS github and does not modify anything in this folder
FreeRTOS-POSIX/ FreeRTOS POSIX wrapper source code. MCU+ SDK simply clones the code from FreeRTOS POSIX github and does not modify anything in this folder
portable/ SDK FreeRTOS porting related files for different CPUs
${SDK_INSTALL_PATH}/source/kernel/freertos/dpl
common/ FreeRTOS DPL APIs that are common across all CPUs
m4/ FreeRTOS DPL APIs that are specific to M4F CPUs
r5/ FreeRTOS APIs that are specific to R5F CPUs
a53/ FreeRTOS APIs that are specific to A53 CPUs
C75/ FreeRTOS APIs that are specific to C75 Core

In addition to above files, to enable features like HW interrupts, cache, MPU, the FreeRTOS library in FreeRTOS SDK also shares some code with NORTOS, see to makefile in the folder source\kernel\freertos to see the exact list of files that are included to build a freertos library.

FreeRTOS usage guidelines

See FreeRTOS usage guidelines for FreeRTOS usage guidelines and comparison to SysBIOS.

Additional references

Given below are some references to learn more about FreeRTOS.

Document Description Web link
Easy to read FreeRTOS book https://www.freertos.org/Documentation/RTOS_book.html
FreeRTOS user docs https://www.freertos.org/features.html
User API reference https://www.freertos.org/a00106.html
FreeRTOS core kernel source code https://github.com/FreeRTOS/FreeRTOS-Kernel
FreeRTOS core kernel example source code https://github.com/FreeRTOS/FreeRTOS/tree/master/FreeRTOS
Additional FreeRTOS.org maintained libraries (POSIX, TCP, Filesystem, …) https://www.freertos.org/FreeRTOS-Labs/index.html \n https://www.freertos.org/FreeRTOS-Plus/index.html \n https://github.com/FreeRTOS

See also

Driver Porting Layer (DPL), NO RTOS