nRF5340 UART driver doesn't exit low power mode when it receives data

[ronbo999]

Hi,

In the attached hello world example that I modified for the nRF5340DK board, the nRF UARTE serial driver doesn't exit low power mode when I type any characters on my TeraTerm window.

If you comment out the following line:

CONFIG_PM_DEVICE_RUNTIME=y

my hello world application starts working correctly.

3173.hello_world.zip

[ronbo999]

I forgot to mention that I'm using NCS 2.9 release.

[Hieu]

Hi ronbo999,

I believe the driver simply doesn't support automatically transition out of low power state.

I will look into whether the general Zephyr driver design convention supports this and see what can be done about it. I will update you this week.

Hieu

[ronbo999]

Hi Hieu,

Before I migrated to NCS 2.9.0, I was on NCS 2.6.1. This same hello world program works in NCS 2.6.1.

As a test, I tested every major NCS releases since 2.6.1. Here are the results:

NCS 2.6.1 - working

NCS 2.7.0 - working

NCS 2.8.0 - does not work

NCS 2.9.0 - does not work

NCS 3.0.0 preview1 - working

This issue with the UART not exiting low power mode got introduced in NCS 2.8. It got fixed again in NCS 3.0.0_preview1.

[lincoln-lu]

ronbo999 Hieu 

I found this issue disappeared after I cherry-picked the the commit below from Zephy-RTOS repo mainline(that is after Zephyr 3.7.99 or NCS 2.9.0)

https://github.com/zephyrproject-rtos/zephyr/commit/13ed9e4210aeed179e9f302bb7fdb7c93af00c0d

[Hieu]

Thanks a lot for sharing your finding, lincoln-lu.

ronbo999, would you like to try that and see if it works?

[ronbo999]

Hi Hieu. The fix suggested by lincoln-lu worked. You can close this ticket. Thanks.