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.

[RK]

This is why I wanted to know what code is running, is it just timed code, at which point it will only task switch at a tick and I'd expect the bottom trace, or are there async events at which point I'd expect something like the top trace (assuming the async events call the yield function properly).

The only case in the middle is where it's timed code but the expected timeout is always one tick, so tickless mode never actually goes tickless and runs around the idle loop. I suppose running tickless and also putting sd_app_evt_wait() in the idle loop might be an interesting test, if it then looks like the bottom trace that would indicate that tickless mode isn't ever really being entered.

But yes knowing whether the code is just timer based or there's an async part to it would be rather helpful.