Quality RTOS & Embedded Software

 Real time embedded FreeRTOS RSS feed 
Quick Start Supported MCUs PDF Books Trace Tools Ecosystem TCP & FAT




Loading

pxHigherPriorityTaskWoken usage clarification

Posted by rsgrimes on August 11, 2016

Three questions, with a bit of background.

Many of the functions that may be safely called from an ISR have a pointer parameter often named pxHigherPriorityTaskWoken. My understanding is that if this is not NULL, and the associated call causes a higher priority task to unblock, then *pxHigherPriorityTaskWoken will be set true, and the calling ISR should call portYIELDFROMISR() prior to returning to activate the unblocked, higher priority task.

  1. Is this a correct understanding?
  2. If portYIELDFROMISR isn't called, then the task will eventually be unblocked, but not until some other event causes the scheduler to reevalute the ready tasks; is that correct?

Finally, I've noticed that the online API documentation (example: http://www.freertos.org/a00119.html) has changed to add this note to the pxHigherPriorityTaskWoken parameter: > "From FreeRTOS V7.3.0 pxHigherPriorityTaskWoken is an optional parameter and can be set to NULL." 3. If you don't supply this parameter, then you won't be notified of a higher-priority task being woken, so it won't get scheduled as soon as possible; is that the sole effect of not using this parameter? 4.


pxHigherPriorityTaskWoken usage clarification

Posted by richard_damon on August 12, 2016

1) Yes. 2) Yes, for example, the tick interrupt. 3) Yes, It isn't quite 'optional', as you have to provide something, but if you pass a NULL (or a 0) then you just don't get the indication that someone has woken. In effect, when/if it is time to set the flag true, that operation is skipped if you pass a null pointer.


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




Copyright (C) Amazon Web Services, Inc. or its affiliates. All rights reserved.

Latest News

FreeRTOS kernel V10 is available for immediate download. Now MIT licensed.


FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

IAR Partner

Microchip Premier RTOS Partner

RTOS partner of NXP for all NXP ARM microcontrollers

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

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

OpenRTOS and SafeRTOS