Quality RTOS & Embedded Software

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


Scheduler behavior in non-preemptive mode

Posted by Tzu-Chien Chiu on August 29, 2006
I have a non-preemptive port of FreeRTOS and there there are totally three tasks:

Task 1, tskIDLE_PRIORITY + 1
Task 2, tskIDLE_PRIORITY + 2

Task 1 and 2 is created using the same function:

portTASK_FUNCTION(task_proc, params)
unsigned id = *(unsigned*) params;
while (1) {
printf("*%d* ", id);

But Task 1 *never* gets a chance to run. After reading vTaskSwitchContext(), I found that Task 1 is starved because Task 2 is *always* in the ready list, and uxTopReadyPriority is always 2.

Is this behavior expected?

Tzu-Chien Chiu - SMedia Technology Corp.
URL: http://www.csie.nctu.edu.tw/~jwchiu/

RE: Scheduler behavior in non-preemptive mode

Posted by Nobody/Anonymous on August 29, 2006
Yes, this would be expected because task 2 never blocks. It is always the highest priority task that is able to run.

If you replaced taskYIELD() with vTaskDelay( 2 ), then task 2 would block for 2 ticks, allowing task 1 to execute.

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

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

Latest News

Version 10.1.0 of the FreeRTOS kernel is available for immediate download. MIT licensed.

View a recording of the "OTA Update Security and Reliability" webinar, presented by TI and AWS.


FreeRTOS and other embedded software careers at AWS.

FreeRTOS Partners

ARM Connected RTOS partner for all ARM microcontroller cores

Espressif ESP32

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

Xilinx Microblaze and Zynq partner