DFU with a compressed LZ4 file

[Markus Arnoldsson]

Hello! 

I am working on a FOTA solution for the nRF52DK, I have followed this example: https://devzone.nordicsemi.com/guides/nrf-connect-sdk-guides/b/software/posts/ncs-dfu

The FOTA works using the nRF Device Manager application and a binary image file.

For the project, it is planned to compress the binary image file with lz4 and in the bootloader of the MCU include a decompressor.

However, in nRF Device Manager it says invalid file when trying to flash the compressed image.

Does anyone have a recommendation to solve this? Other plans work as well, in general what is needed is for a lz4 compressed file to be flashed onto the MCU.

[Aleksander Nowakowski]

Hello,

The app is checking few first bytes of the binary and it's expecting to find there a Magic value. If your binary is compressed, encrypted, etc, it will fail and return an error. 

I recommend downloading the source code of the app and removing the code with the checks.

[Markus Arnoldsson]

Hello again. I found the other invalids, I removed all checks except one which I am a little bit confused by, maybe you can help me.

In ImageUpgradeViewmodel there are two invalid checks:

https://github.com/NordicSemiconductor/Android-nRF-Connect-Device-Manager/blob/main/sample/src/main/java/io/runtime/mcumgr/sample/viewmodel/mcumgr/ImageUpgradeViewModel.java

They are both in the upgrade() function, in two different try/catch.

The first one I believe can just be removed by the following:

The second one however has a function call at the bottom: manager.start(images, eraseSettings) which needs a catch for exception. In the catch it gives out "Invalid image file.".

I'm not sure how this check shall be removed, or if it has to do with the bootloader of the MCU (we have not implemented decompression in the bootloader yet).

[Aleksander Nowakowski]

Perhaps you need to modify the library as well. Just follow the rabbit. Just check where it crashes and try work around.