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

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

ronbo999 — Fri, 14 Mar 2025 12:50:15 GMT

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

Hieu — Thu, 13 Mar 2025 11:50:51 GMT

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

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

lincoln-lu — Thu, 13 Mar 2025 05:28:48 GMT

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

ronbo999 — Wed, 12 Mar 2025 14:38:32 GMT

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.

Hieu — Tue, 11 Mar 2025 22:56:25 GMT

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 — Tue, 11 Mar 2025 03:24:46 GMT

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