nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

RE: nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

Vidar Berg — Thu, 04 Dec 2025 07:04:59 GMT

Good to hear that it works now and thanks for the update. Yes, changing the default clock source in the board files is a best solution. I wasn't sure earlier if you had defined your own board or if you used the nrf5340DK board as your build target

RE: nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

Khldun — Wed, 03 Dec 2025 15:25:29 GMT

Thank you very much for your help!

The issue is now resolved. I added the LFCLK configuration options to my custom board's defconfig file. This ensures that all images (Application Core, Network Core, MCUboot, etc.) built for this board automatically use the internal RC oscillator instead of the external LFXO

RE: nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

Vidar Berg — Wed, 03 Dec 2025 10:33:16 GMT

When you don't have an external LF crystal it is recommended to select the internal LF RC oscillator by enabling the CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC setting. It is important that you not only apply this to your main application, but also any bootloader's and to your ipc_radio build.

You can check whether this setting is currently applied or not for ipc_radio by looking at the generated build/ipc_radio/zephyr/.config file.

[quote user="Khldun"]Since my custom board does not have an external 32.768 kHz crystal, should I disable the LFXO node in my device tree overlay like this?[/quote]

Yes.

RE: nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

Khldun — Tue, 02 Dec 2025 13:01:54 GMT

Thank you for your response.

I found the following LFXO configuration in my device tree file. Could this be causing the issue?

Additionally, I checked the generated build/zephyr.dts and found this output for the clock controller...

			/* node '/soc/peripheral@50000000/clock-controller@4000' defined in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:15 */
			oscillators: clock-controller@4000 {
				compatible = "nordic,nrf53-oscillators"; /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:16 */
				reg = < 0x4000 0x1000 >;                 /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:17 */

				/* node '/soc/peripheral@50000000/clock-controller@4000/lfxo' defined in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:19 */
				lfxo: lfxo {
					compatible = "nordic,nrf53-lfxo";     /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:20 */
					#clock-cells = < 0x0 >;               /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:21 */
					clock-frequency = < 0x8000 >;         /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:22 */
					load-capacitors = "internal";         /* in custom/boards/arm/custom_nrf53/nrf5340_cpuapp_common.dtsi:262 */
					load-capacitance-picofarad = < 0x7 >; /* in custom/boards/arm/custom_nrf53/nrf5340_cpuapp_common.dtsi:263 */
				};

				/* node '/soc/peripheral@50000000/clock-controller@4000/hfxo' defined in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:25 */
				hfxo: hfxo {
					compatible = "nordic,nrf53-hfxo"; /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:26 */
					#clock-cells = < 0x0 >;           /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:27 */
					clock-frequency = < 0x1e84800 >;  /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:28 */
					startup-time-us = < 0x578 >;      /* in zephyr/dts/arm/nordic/nrf5340_cpuapp_peripherals.dtsi:29 */
				};
			};

Since my custom board does not have an external 32.768 kHz crystal, should I disable the LFXO node in my device tree overlay like this?

&lfxo {
    status = "disabled";
};

Would this resolve the hang at SLEEP_IF_ALLOWED(__WFE) that I'm experiencing?

RE: nRF5340 Custom Board Hangs at WFE (Idle) After Migration from NCS v2.4.0 - No External 32.768 kHz Crystal

Turbo J — Tue, 02 Dec 2025 12:05:23 GMT

Check finished DTS in build/zephyr. There were DTS LFXO changes IIRC.