FreeRTOS tick count invalid when using tickless idle

[Paolo D]

I've encountered a problem getting the tick count from FreeRTOS when tickless idle is enabled. I'm not sure if this is a bug or just unexpected behavior. I am using the latest nRF5 SDK 11, and observed this with the nRF52. It looks like the same problem should also occur with the nRF51.

When calling xTaskGetTickCount() immediately after the system has woken from the idle state, but before the next tick interrupt after waking up has occurred, the tick count doesn't take into account the time spent idle. As soon as the first tick occurs after waking up, the tick count jumps ahead to the correct value.

The reason is that the vPortSuppressTicksAndSleep function in port_cmsis_systick.c doesn't call vTaskStepTick to account for the time spent idle. Instead it waits for xPortSysTickHandler to call it.

In the ARM_CM4F port of FreeRTOS, which uses SysTick as the tick source, the vPortSuppressTicksAndSleep function does call vTaskStepTick as soon as it wakes up when tickless idle is enabled.

[Anders Strand]

Hello.

As you say, this is caused by how the tickless mode is implemented. The issue has been reported internally, and will probably be changed in an upcoming release. Thanks for reporting this.

-Anders

[Michael Dierks]

Is there any further information regarding this? I am having issues with the xNextTaskUnblockTime syncing with the xTickCount. Sometimes the tickcount is jumping ahead of the unblocktime in places it seems it should not be moving, which results in odd behavior. Trying to isolate a problem when I came across this post. Just thinking it may be related.

[Anders Strand]

This is now a know bug, see this thread.

[WestCoastDaz]

Anders,

We are using your implementation of you posted in this thread devzone.nordicsemi.com/.../ and I am still seeing missing ticks. I reviewed some of the FreeRtos demo port implementations and they all seem to call vTaskStepDiff() unconditionally. Is there a way to debug the tick count?

Thanks

[Radoslaw Koppel]

What do you mean by missing ticks? Single ticks are lost or there is still the problem when calling xTaskGetTickCount() early after wakeup?

[Susheel Nuguru]

Darren, I know that this is late response. If you were seeing this in tickless mode Can you follow this thread and see if these fixes help you.