[riot-devel] xtimer and lower core/bus frequency in low power mode

Michael Andersen michael at steelcode.com
Tue Sep 13 02:50:06 CEST 2016


imho, xtimer should be implemented off the lowest power timer. I don't know
that MCU that well but there is usually some kind of RTC timer or systick
that runs even in the lowest power sleep mode, at the same frequency all
the time.

On Mon, Sep 12, 2016 at 5:22 PM, Anon Anonymous <anon1644072 at gmail.com>
wrote:

> Good day everyone,
>
> I implemented low power mode for STM32L151-based board and looking for a
> solution of following problem.
>
> When xtimer_sleep(10) executed, the MCU meant to go into low power mode
> for 1 second.
> Assume that current clock frequency is 32 MHz, after I lower frequency to
> 4MHz MSI and entered to sleep, the timer will runt 8 times slower and
> xtimer_sleep(1) becomes xtimer_sleep(8) due to lower bus (and thus, timer)
> clock frequency.
>
> How I should make xtimer aware about lower clock frequency? I tried to
> directly modify xtimer's TIM5 prescaler with no luck.
>
> Best regards,
> Anon
>
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