[riot-devel] Low-Power-/Low-Frequency Timer as source for xtimer

Bernhard Nägele bernhard at naegele-privat.de
Thu Jun 2 12:57:58 CEST 2016


Hello RIOT-Developers,

I've sent already a message about the topic of using a 
low-power-/low-frequency timer as a source for xtimer in february, but I 
want to discuss this topic again.
The STM32L0 series of ST microcontrollers provide such a timer (LPTIM - 
like it is also available on Kinetis controllers). I want to use the 
STM32L0 STOP-Mode for getting very low power-consumpion in the breaks 
between measurements. The idea is to wake up the microcontroller 
periodically from the low-power STOP-Mode (with LPTIM used as 
wake-up-timer) like it is done in the xtimer_usleep_until example.
However - I greped through the RIOT code and I have seen that the xtimer 
is used somewhere else also for inserting some small delays. If you use 
the low-speed timer of the microcontroller as source of the xtimer you 
loose the fine granularity for those "short delays".
Wouln't it be a good idea (for the whole project) to define two separate 
timers - one for short delays (u-second granularity) and one for 
power-saving-modes?
What is your idea about that? How could this problem be solved with the 
existing implementation?

Thanks a lot!

Best regards,
Bernhard


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