[riot-devel] GNRC with sleepy nodes

Joakim Nohlgård joakim.nohlgard at eistec.se
Wed Nov 22 13:39:44 CET 2017


Hi,

On Tue, Nov 21, 2017 at 5:26 PM, Daniel Evans <photonthunder at gmail.com> wrote:
> First, I should add that I currently have a working samd21 low power
> implementation but to accomplish that I use rtt.c for my always running
> clock and then standby sleep the module whenever it gets to the idle task.
> This is a hack and is not a clean implementation and means you don’t use
> XTIMER and no use of the nice built in protocols, I have my own hacked LoRa
> mesh network.
>
> Referring specifically to the samd21, which includes the samr21 and loosely
> the saml21, this is the path as I see it for getting low power working
> natively with RIOT:
>
> 1) Add a method to make setting up the generic clocks that includes run in
> standby and on demand options.
> 2) Add flags for peripherals so that you can set the clock and run in
> standby
> 3) Tweak XTIMER so that it can be run by a low power 32kHz clock when
> sleeping

I am using xtimer with 32768 Hz clocking, on the Kinetis platform (PR:
https://github.com/RIOT-OS/RIOT/pull/7897). It's not an issue with
xtimer itself, more of a question of high performance, 1 µs precision
vs. low power, ~30 µs tick precision (but because of delays in the low
power timer hardware it's more like 90-150 µs precision on my dev
board).
There are many applications where it does not matter if the timer
delay is not exact, as long as it does not drift too much.

>
> All of these things have been discussed and are in the works and are on the
> list but not currently top priority.  Low power is critical for my
> application and I am a little surprised it isn’t for more users, but I
> imagine others just hack around it as well?

It's critical for most of our applications as well, but I have not had
time to properly wrap things up in nice PRs. We have some coming
projects which will need even more low power optimizations which
should be upstreamed once they are working and we have had some time
to clean it up.

>
> Hope that helps a little,
>
> Dan
>
>
> On Nov 21, 2017, at 6:07 AM, Francisco Molina <francisco.molina at inria.cl>
> wrote:
>
>
>>Issues #7743 and #7332 both discuss the problem.
>>
>>Dan
>
> I saw those issues but they only refer to the fact that xtimer doesn't run
> during sleep modes, is that the only issue? Cheers
>
> Francisco

Best regards,
Joakim


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