Zephyr + NRF5340: change GPIO function in runtime

[Bruno Saraiva]

The project uses nRF5340. A signal is connected to P0.27/AIN6, and during "normal" mode the pin is used as an ADC.

Before going into sleep mode we would need this pin to become a GPIO Input with enabled interrupt, so as to waking up the MCU (and then back again to ADC during "normal mode").

Some previous posts state that Zephyr did not allow for runtime configuration of pins. Is that still the case? If this is not available and we use direct configuration of the MCU's registers, what are the "special concerns" in the device tree that we have to take in order not to mess up Zephyr usage of the pin?

[Bruno Saraiva]

Hi Simon,
Thank you for the attention! We will implement this on our side to see how it goes.
Before I deeply analyze your code, reading from your description, it seems that the solution involves configuring both options in Zephyr's Device Tree and then "disable" the one not being used directly by register control in run time...
I hope that this post becomes useful for more people up ahead.
Cheers
Bruno

[Simon]

Bruno Saraiva said:

Before I deeply analyze your code, reading from your description, it seems that the solution involves configuring both options in Zephyr's Device Tree and then "disable" the one not being used directly by register control in run time...

Actually, I did not configure the ADC analog input pin and the interrupt pin in the Device Tree (DT). But if you want to do it the "proper" way, you should probably do it through the DT.

Take a look at this reply to understand how to configure the ADC through the DT: https://devzone.nordicsemi.com/support-private/support/257472#permalink=606106

Take a look at this DevZone case to see how to configure the gpio interrupt pin through the DT: https://devzone.nordicsemi.com/f/nordic-q-a/72618/extra-gpios-in-board-overlay-for-nrf9160dk

Best regards,

Simon

[Bruno Saraiva]

So this is where I get confused - pardon me for the lack of experience with Zephyr:
We know how to configure the pin using DT for EITHER of those functions... but what is the best practice when we need both? Can I simply ignore DT completely for this "dual function" pin? Or should I configure both functions of the pin in DT and disable the via register as mentioned? Note that the project has a ton of other devices configured in DT, so that layer will still be there for the rest of the hardware.

[Simon]

I don't think there should be any conflict in the device tree regarding the pin if you configure both the adc and the interrupt pin in the DT, this is because you don't set the pin option for the ADC in the DT. As mentioned by Heidi in this reply: 

"Please note that you still need to configure the actual analog inputs (AIN0 to AIN7) in the main file"

So, if you would like to use P0.04, you need to use Analog input associated with that pin, which is AIN0 (hard wired).

Take a look at the sample /zephyr/samples/boards/nrf/battery to see how it's done.