nRF5340 OTA: App core reverted but Net core updated successfully – how to synchronize rollback?

[Woobin Song]

Hi,

We are developing a product based on nRF5340(ncs 3.1.0) and using MCUboot for OTA updates of both app core and net core.

During an OTA update, the following issue occurred:

• The net core firmware was updated successfully.

• However, due to a watchdog reset or an unknown issue, the app core did not reach main() and therefore could not confirm the OTA update.

• As a result, MCUboot reverted the app core firmware to the previous version.

• The net core remained updated to the new version.

• After reboot, BLE advertising did not work properly.

So we ended up with a mismatched state:

• App core: reverted to the old firmware

• Net core: running the new firmware

My questions are:

1. Is there a recommended way to synchronize rollback between app core and net core on nRF5340?

2. If the app core OTA fails and is reverted, is it possible to automatically revert the net core firmware as well?

3. Are there any best practices or reference designs for handling partial OTA success on nRF5340?

Any guidance or references would be greatly appreciated.

Thank you in advance.

[Woobin Song]

Additionally, in a real-world scenario, it is also possible that the battery is removed at an unfortunate timing during the OTA update process. This could lead to a similar situation where only one core is updated while the other is reverted.

[Amanda Hsieh]

Hi Woobin, 

Please see the limitation in the note of the Simultaneous multi-image DFU with nRF5340 DK:

The application core can be reverted, but doing so breaks the network core upon reversal, as the reversion process fills the network core with the content currently in the RAM that PCD uses.

Be aware that reverting the app core after such an update is unsafe for the net core, so it should minimize the chance of reverting (e.g., robust watchdog handling, early confirmation strategy), or avoid interface‑breaking changes.

Woobin Song said:

in a real-world scenario, it is also possible that the battery is removed at an unfortunate timing during the OTA update process. This could lead to a similar situation where only one core is updated while the other is reverted.

It should use Simultaneous multi-image DFU with nRF5340 DK to update both cores in one operation. See this tutorial https://academy.nordicsemi.com/simultaneous-updates-for-both-cores-of-the-nrf5340/

Regards,
Amanda H.

[Woobin Song]

Hi Amanda,

Thank you for the clarification and the detailed explanation.

BR,

Woobin