Quality RTOS & Embedded Software
About   Contact   Support   FAQ

 Real time embedded FreeRTOS RSS feed 
Real time embedded FreeRTOS mailing list 
Quick Start Supported MCUs Books & Kits Trace Tools Ecosystem TCP & FAT Training

Last site update June 02 2015

[More about tasks...]

The FreeRTOS Tutorial Books provide additional detailed information on tasks and their behaviour.

Task Priorities

Each task is assigned a priority from 0 to ( configMAX_PRIORITIES - 1 ), where configMAX_PRIORITIES is defined within FreeRTOSConfig.h.

If the port in use implements a port optimised task selection mechanism that uses a 'count leading zeros' type instruction (for task selection in a single instruction) and configUSE_PORT_OPTIMISED_TASK_SELECTION is set to 1 in FreeRTOSConfig.h, then configMAX_PRIORITIES cannot be higher than 32. In all other cases configMAX_PRIORITIES can take any value within reason - but for reasons of RAM usage efficiency should be kept to the minimum value actually necessary.

Low priority numbers denote low priority tasks. The idle task has priority zero (tskIDLE_PRIORITY).

The FreeRTOS scheduler ensures that tasks in the Ready or Running state will always be given processor (CPU) time in preference to tasks of a lower priority that are also in the ready state. In other words, the task placed into the Running state is always the highest priority task that is able to run.

Any number of tasks can share the same priority. If configUSE_TIME_SLICING is not defined, or if configUSE_TIME_SLICING is set to 1, then Ready state tasks of equal priority will share the available processing time using a time sliced round robin scheduling scheme.

[ Back to the top ]    [ About FreeRTOS ]    [ Sitemap ]    [ ]

Copyright (C) 2004-2010 Richard Barry. Copyright (C) 2010-2015 Real Time Engineers Ltd.
Any and all data, files, source code, html content and documentation included in the FreeRTOSTM distribution or available on this site are the exclusive property of Real Time Engineers Ltd.. See the files license.txt (included in the distribution) and this copyright notice for more information. FreeRTOSTM and FreeRTOS.orgTM are trade marks of Real Time Engineers Ltd.

Latest News - New Book Edition!

Receive a complimentary pre-release pdf of our up-coming book "Mastering the FreeRTOS Real Time Kernel, a Hands-On Tutorial Guide" with every purchased copy of the existing "Using the FreeRTOS Real Time Kernel" book.

Sponsored Links

⇓ Now With No Code Size Limit! ⇓
⇑ Free Download Without Registering ⇑

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Renesas Electronics Gold Alliance RTOS Partner.jpg

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

Atmel RTOS partner supporting ARM Cortex-M3 and AVR32 microcontrollers

STMicro RTOS partner supporting ARM7, ARM Cortex-M3, ARM Cortex-M4 and ARM Cortex-M0

Xilinx Microblaze and Zynq partner

Altera RTOS partner for Nios II and Cortex-A9 SoC

Freescale Alliance RTOS Member supporting ARM and ColdFire microcontrollers

Infineon ARM Cortex-M microcontrollers

Texas Instruments MCU Developer Network RTOS partner for ARM and MSP430 microcontrollers

Cypress RTOS partner supporting ARM Cortex-M3

Fujitsu RTOS partner supporting ARM Cortex-M3 and FM3

Microsemi (previously Actel) RTOS partner supporting ARM Cortex-M3

Atollic Partner

IAR Partner

Keil ARM Partner

Embedded Artists