Quality RTOS & Embedded Software

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


vTaskDelayUntil and short delays

Posted by Jerry Durand on August 22, 2013
I did a forum search but it didn't seem like this has been mentioned.

So... I'm starting a project where the delay time for vTaskDelayUntil will be variable and could be really short.

If the delay until time (xLastWakeTime plus xPeriod in your example) generates an end time that has already past, does this return immediately (good) or wait for the clock to roll over (bad) crash (worse)?


xLastWakeTime is set to 1000
{ do things that take 2 ticks }
xPeriod = 1;
vTaskDelayUntil( &xLastWakeTime, xPeriod );
// the wakeup time is now 1001 but the clock time is 1002.

RE: vTaskDelayUntil and short delays

Posted by Jerry Durand on August 22, 2013
I guess I have one more question, is the xLastWakeTime now 1001 or 1002? ie: is it the calculated wakeup time or the time it actually woke up?

RE: vTaskDelayUntil and short delays

Posted by Jerry Durand on August 22, 2013
I wrote some test code for to try this out. To simulate a busy system I made a loop with vTaskDelay(2); in front of the vTaskDelayUntil. I used a variable for xPeriod and with the debugger kept decreasing it to see what it would do.

With xPeriod of 2 or higher, the period WAS 2.
With xPeriod of 1 the period was still 2, so instant return (good work!)
With xPeriod of 0, the system hangs. I can live with that.

So, as long as I verify xPeriod is greater than zero, I don't need to worry about this low priority task crashing when the system gets busy.

RE: vTaskDelayUntil and short delays

Posted by MEdwards on August 22, 2013
If you step into the function you will see near the top an assert to trap 0 being passed in.

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

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

Latest News

NXP tweet showing LPC5500 (ARMv8-M Cortex-M33) running FreeRTOS.

Meet Richard Barry and learn about running FreeRTOS on RISC-V at FOSDEM 2019

Version 10.1.1 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