System / BLE only starts after J-Link RTT is connected (custom board, no DCDC) – fixed in NCS v2.5.1, same issue again in v2.9.2

[mento]

Hello,I am using a custom nRF52832-based board that has no DCDC circuitry (LDO only).What happened in NCS v2.5.1

• After power-on, the system did not start (e.g. no BLE advertising).

• The system only started after I connected J-Link RTT Viewer to the board.

• I spent a lot of time adjusting configuration (DCDC, clocks, RTT/console, etc.) and eventually got it working so that the system starts correctly after power-on without the debugger connected.

What happened after upgrading to NCS v2.9.2

• I upgraded to NCS v2.9.2 because v2.5.1 does not support ANT.

• The same problem came back: the system does not start on power-on; it only starts after I connect J-Link RTT Viewer to the board.

• I have tried to apply the same settings that fixed the issue in v2.5.1 (disabling DCDC in software, 32 kHz internal RC, disabling RTT / console, delays before BLE init, etc.), but the problem persists in v2.9.2.

Question

• What changed between NCS v2.5.1 and v2.9.2 that could cause this “no start until RTT is connected” behavior again on a custom board without DCDC?

• Is there any recommended configuration or workaround for NCS v2.9.2 so that the system (and BLE) starts reliably after power-on without requiring J-Link RTT to be connected?

Thank you for your help.

[Vidar Berg]

Hello,

The initial regulator mode is now defined in the devictree and if you are using the nrf52dk as your build target, the DCDC regulator will be enabled by default (https://docs.nordicsemi.com/bundle/ncs-3.1.1/page/zephyr/releases/migration-guide-4.0.html#regulator, https://github.com/nrfconnect/sdk-zephyr/blob/a0e545cb437a44b6f9cd176ef28a055403f8d2d8/boards/nordic/nrf52dk/nrf52dk_nrf52832.dts#L138)

You can include the following in your devicetree overlay to select the LDO:

&reg {
	regulator-initial-mode = <NRF5X_REG_MODE_LDO>;
};

 

Best regards,

Vidar

[mento]

I added the devicetree overlay with &reg { regulator-initial-mode = <NRF5X_REG_MODE_LDO>; }; as suggested. BLE still only starts after J-Link RTT is connected. On the same custom board (no DCDC), the same approach worked in NCS v2.5.1. Is there any other change in v2.9.2 (init order, clock, or regulator driver) that could cause this? Thank you.

[Vidar Berg]

Does your project include other FW images in the build such as MCUBoot? In that case, are you applying the overlays to those images as well?

[mento]

Yes. The project uses sysbuild and includes MCUBoot. We applied the LDO overlay to the application (boards/nrf52dk_nrf52832.overlay with &reg { regulator-initial-mode = <NRF5X_REG_MODE_LDO>; };) as you suggested. For MCUBoot, we tried adding the same overlay in sysbuild/mcuboot/boards/nrf52dk_nrf52832.overlay, but the MCUBoot CMake configure then failed, so we are not using a devicetree overlay for MCUBoot. We also tried CONFIG_BOARD_ENABLE_DCDC=n in child_image/mcuboot.conf, but that caused a configure failure (this board/Kconfig may not define that option). So at the moment only the application uses the LDO overlay and in-code DCDC disable; MCUBoot uses the board default. BLE still only starts after J-Link RTT is connected; without RTT it does not start. Could you advise how to apply the regulator (LDO) overlay to the MCUBoot image correctly in sysbuild, or whether applying it only to the application is sufficient for a custom board without DCDC? Thank you.

[Vidar Berg]

mento said:

n sysbuild/mcuboot/boards/nrf52dk_nrf52832.overlay, but the MCUBoot CMake configure then failed, so we are not using a devicetree overlay for MCUBoot. We

For this to work you must also provide the sysbuild/mcuboot/prj.conf file to replace the default prj.conf file from the mcuboot module. Another alternative to this is to remove the mcuboot directory in sysbuild and replace it with an overlay named mcuboot.overlay (Ref. https://docs.nordicsemi.com/bundle/ncs-2.6.1/page/zephyr/build/sysbuild/index.html#zephyr_application_kconfig_fragment_and_devicetree_overlay).