DevAcademy - nRF Connect SDK Intermediate - Lesson 9 Exercise 5 - Unable to find bootable image

[Ken Yoshioka]

The solution for "nRF Connect SDK Intermediate - Lesson 9 Exercise 5" does not appear to boot-up after flashing and gives the following output on the com port:

*** Booting MCUboot v2.1.0-dev-9b4ae4cbc9e2 ***
*** Using nRF Connect SDK v3.1.1-e2a97fe2578a ***
*** Using Zephyr OS v4.1.99-ff8f0c579eeb ***
W: Failed reading sectors; BOOT_MAX_IMG_SECTORS=128 - too small?
E: Image in the primary slot is not valid!
E: Unable to find bootable image

It worked fine on nRF54L15-DK, but it's not working on the nRF54LM20-DK.

Here is my set-up:

• Hardware:  nRF54LM20-DK

• nRF Connect SDK: v3.1.1

• nRF Connect Toolchain: v3.1.1

• nRF Connect for VS Code: 2025.9.798

[Menon]

Hello Ken,

I tested the same sample using the DK and was able to reproduce the same error message on my side. I’m currently working on this and will update you once I have more information.

The sample in DevAcademy is a modified version of peripheral_lbs, demonstrating how to add DFU support to an application. There isn’t an exact equivalent sample, but Zephyr does provide the smp_server sample, which showcases image management and DFU over BLE using SMP. However, it’s not a fully out-of-the-box BLE OTA solution.

Kind regards,
Abhijith

[Ken Yoshioka]

Hi Abhijith,

Thanks for confirming the issue and looking into it. I’ll work with the smp_server example in the meantime and wait for your update once you have more details.

Best regards,
Ken