FreeRTOS Tickless Idle vs Tick Current Consumption

[WestCoastDaz]

We have been comparing the current consumption of the nRF52 running FreeRTOS Tickless Idle versus a constant tick and using the idle task to sleep and the results are interesting, see below.

June 7th Edit: SDK 11, SoftDevice S132 2.0.0.0, Silicon is QFAABB (Rev C)

Tickless Idle:

• Average current is 390uA

Tick with Idle Task:

• Average current is 303uA

Both runs were identical with the floating point interrupt handler implemented as in this post devzone.nordicsemi.com/.../, same number tasks/execution profile, same tick rate, advertising off. The only difference is tick mode uses the idle task hook to put the processor to sleep.

Note the follow images were captured using our own Labview tool sampling at 8kHz. Ignore the bottom trace

Tickless Idle

Tick with Idle Task

[RK]

I also can't figure out what on earth would produce those results.

What's running on the chip, do you have the softdevice loaded and active, is it doing anything at all? The tickless mode should be showing less than the other one, if it has nothing scheduled then it should put itself to sleep for seconds or minutes or basically forever.

Are you sure you've got this test right? Because it really makes no sense at all.

[WestCoastDaz]

RK,

So I have some more to add to this thread thanks to your blog post on the Segger SystemView devzone.nordicsemi.com/.../ see above for a snapshot from a run with tickless idle enabled (the idle task hook is disabled). Note I re-purposed the FreeRTOS configPreSleepProcessing(x) and configPostSleepProcessing(x) to record the expected number of sleep ticks. It appears that FreeRTOS prepares to go to sleep, enters sleep and then immediately wakes up for some un-instrumented reason and then goes back to prepares to go back to sleep and succeeds.

Any thoughts would be greatly appreciated. Thanks, Darren