[TriEmbed] some progress with sleep modes using Arduino M0 (ATSAMD21)

[Pete Soper]

Thanks for the update, Alex. This is very interesting.

-Pete


On 02/22/2018 09:03 AM, Alex Davis via TriEmbed wrote:
> I finally got my Adafruit M0 Adalogger board to sleep without 
> crashing, as well as to get a LIS3DH accelerometer to do both event 
> interrupt triggering and continuous readout. It’s not a full success, 
> however, as measuring current draw shows the M0 does not always go to 
> actual low-power mode. The best I have achieved so far as about 2mA - 
> that’s pretty poor. Worst case “sleep” was 18 mA.
>
> I’m using the LowPower.h library. Yes, that is lazy and I should be 
> setting the registers manually etc…
>
> I think also there are some subtleties with the ATSAMD21 concerning 
> the stack and vectors with interrupts and sleep. If I keep my 
> sleep/wake within main(), it works fine, but if I try do it within a 
> function as part of a switch-case state machine, it fails or appears 
> to run the wrong code.
>
> I would not recommend the ATSAMD21 for low-power projects when using 
> Arduino. The Adafruit M0 products in particular do not have a JTAG 
> interface, so you’re reduced to using LEDs to try to debug, since 
> sleeping shuts down the USB serial interface. I think if you want to 
> use the Feather stuff and want low-power, stick with the 32u4 models.
>
> I put my working and non-working code here on my github: 
> https://github.com/quarterturn/feather-m0-sleep-shake-project
>
> I can probably accept a 2mA draw in sleep mode. I have a 110 mAh 
> battery, and at 2 mA standby and the occasional 15 mA during recording 
> it should last a whole night. I just have to figure out why the exact 
> same sleep command behaves differently at times.
>
> Alex
>
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