[riot-devel] Timers (caution: long mail, abstract available)

Pekka Nikander pekka.nikander at iki.fi
Sat Sep 20 07:12:57 CEST 2014


> I tried to analyze the use cases for timers in RIOT and put the needed functions into groups. I further put in some ideas about possible implementations.
> 
> ...

> To conclude: I think we should be able to create a generic timer infrastructure with 3 submodules:
> - directly used low-level timer drivers for high-res, short periods
> - something like our vtimer for medium to long-term waiting
> - a central timer thread based on the above for sending messages on timeouts and for periodic triggers

Looks reasonable to me.  I think the latter two should be relatively simple and straightforward to implement given the current structure.

The low-level interface may require more thinking, and may be quite tricky given the desire to support quite different chips.

--Pekka

PS.  PFM stands for Pulse Frequency Modulation.  PWM, PFM, and them combined are used in modern SMPS (switching mode power supply) controllers.  The frequency range is from tens of kHz to a few MHz, in experimental systems tens or hundreds of MHz.  PFM is usually not directly implementable with just a timer, but fixed PWM (without a feedback loop) can be implemented relatively easily with a timer and a DMA.  If feedback is needed, then then typically CPU needs to be involved.
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