FreeRTOS xTaskGetTickCount() erroneously skips ahead

[asvatik]

xTaskGetTickCount() erroneously skips ahead after every 65536 ticks. So when calculating timing using values returned by xTaskGetTickCount(), there are problems!

 

vTaskDelay() has no problems. The problem is with xTaskGetTickCount()...

 

For example:

Code:

 

 

TickType_t tickCount1, tickCount2;
while (1) {
	tickCount1 = xTaskGetTickCount();
	vTaskDelay(25);
	tickCount2 = xTaskGetTickCount();
	printf("[%ld] %lu ms have passed!\r\n",
			tickCount2, (tickCount2-tickCount1));
}

 

Output:

 

[64887] 25 ms have passed!
[64912] 25 ms have passed!
[64937] 25 ms have passed!
[64962] 25 ms have passed!
[66087] 1125 ms have passed!
[66112] 25 ms have passed!
[66137] 25 ms have passed!
[66162] 25 ms have passed!
[66187] 25 ms have passed!

 

 

Workaround is to use vTaskDelay() instead:

 

 

TickType_t tickCount = 0;
while (1) {
	vTaskDelay(25);
	tickCount += 25;
	printf("[%ld] %lu ms have passed!\r\n",
		xTaskGetTickCount(), tickCount);
}

 

 

PLATFORM:

Microprocessor: STM32L496xx (ARM Cortex-M4)

GNU Tools for STM32 (11.3.rel1)

FreeRTOS API CMSIS v2

FreeRTOS version 10.3.1

CMSIS-RTOS version 2.00

[liaifat85]

Here was a similar problem I think: https://forums.freertos.org/t/1-tick-delayed-task-start-after-portsuppress-ticks-and-sleep/6498/19

[asvatik]

There is no problem with FreeRTOS. I let myself become fooled.

If I move my test-code to a separate task with a high enough priority, I am unable to reproduce the problem.