How to ensure only UART peripheral consumes power in NUS example on nRF5340?

[pal_722]

Hi Nordic team,

I’m working with the nRF5340 using the Bluetooth: NUS (Nordic UART Service) example from the Zephyr SDK. Since this example primarily uses the UART peripheral, I want to make sure that only UART is active and consuming power, and that all other unused peripherals are fully disabled or in sleep mode to optimize power consumption.

Here are my questions:

1. Are other peripherals (like I2C, SPI, SAADC, TIMERs, etc.) automatically initialized or consuming power in the default NUS example, even if they’re not explicitly used?

2. What’s the recommended way to ensure that only UART and the BLE stack are active, and all other peripherals are disabled to reduce power?

3. Should I modify the Device Tree (.overlay file) to set unused peripherals to status = "disabled"?

4. Are there any Zephyr configurations (prj.conf) I should be aware of that implicitly enable drivers or subsystems that may consume power (e.g., logging, console, watchdog)?

My goal is to achieve the lowest possible current consumption when the device is idle (BLE connected, UART idle) while ensuring only the necessary modules are powered.

Any guidance or example overlays/configs would be very helpful.

Thanks in advance!

[Vidar Berg]

Hello,

Only the UART needs to be actively disabled in this sample. When UARTE with RX reception is enabled, it forces the HF clock to remain active during sleep. I posted a modified version of this sample that only keeps UART enabled while BLE is connected: RE: Suspending UART Async using PM_DEVICE ACTION_SUSPEND causes crash.  

General power optimization recommendations: https://docs.nordicsemi.com/bundle/ncs-3.1.0-preview3/page/nrf/test_and_optimize/optimizing/power.html 

Best regards,

Vidar

[pal_722]

Hi Vidar Berg 

Thank you for the reply. Will look into the solution given.

So do you also mean to say, the other peripherals need not be exclusively disabled for better power optimization ?

Regards,
Pallavi