Merged.hex and app_signed.hex for FOTA

[inyourface]

Hi 

We are working on the FOTA based on http_application_update project. The hardware is Thingy91. 

The issue is if we use the default the MCUBootloader on Thingy91(version 1.0.2) and program the app_signed.hex via USB. Thingy91 downloads the firmware from the server, but Thingy91 could not load the downloaded firmware after reboot. 

On the other hand, if we program the merged.hex of the same http_application_update application from JTAG. FOTA works and Thingy91 loads the downloaded firmware after reboot.

1. Is it because of the MCUbootloader has to be updated with the application together for FOTA since the default MCUbootloader does not know the starting address of the new downloaded firmware?

2. How can we program the merged.hex via USB? Program zephyr.hex and app_signed.hex separately ? We prefer to use USB over JTAG to update the Thingy91's firmware.

Face

[Martin Lesund]

Hi Face,

it sounds to me like your application uses a different flash partitioning scheme than the asset_tracker, which is what is running on the Thingy:91 by default.

If this hypothesis is correct, then it is the boot_write_img_confirmed() that is the failing part.

What happens, is the bootloader already on your chip, and your application have two different opinions about where the image metadata is stored in the flash.

Your application could therefore write that it is OK to the "wrong" address. E.g. if your application is writing to address 0x80000, but the bootloader is checking address 0x75000, the bootloader will not see that the application has set the OK flag. It will then assume that the image is not OK, and revert.

The reason for this happening, is that the flash partitioning is decided at build time, depending on your application's need, by the Partition Manager script.

The way you get around this problem, is to use a give the Partition Manager a static configuration file: https://developer.nordicsemi.com/nRF_Connect_SDK/doc/1.3.0/nrf/scripts/partition_manager/partition_manager.html#static-configuration

While letting the Partition Manager create the partition map dynamically is fine during development, you will eventually want to use a static partition configuration of your own, to make sure that future versions of your application uses the same partition map.

You can find the partition map used by the asset_tracker on the Thingy:91 here: https://github.com/nrfconnect/sdk-nrf/blob/master/applications/asset_tracker/configuration/thingy91_nrf9160ns/pm_static.yml

If you add that file to your project (either copy the file so it is next to the CMakeLists.txt file in your project, or see the asset_tracker's CmakeLists.txt file to see how you can specify the path), you should be able to "upgrade" from the asset_tracker to your project.

(Also see this similar thread https://devzone.nordicsemi.com/f/nordic-q-a/65765/thingy-91-fota-reverting-unless-flashed-merge-hex-with-jtag )