How to use DFU OTA with custom FW

[rmarques]

Hello, we are using 3 nRF52840 DKs, NSDK 15.2, Mesh SDK 3.1.0, SoftDevice 6.1.0 and Segger Embbeded Studio as my IDE.

I have followed the documentation here to program some boards over the air and had SOME success.

I understood that the process has 5 major steps

1 - Generate private and public keys

2 - Generate DFU archive using an application hex file and the private key

3 - Generate Device Page, adding the public key to the <bootloader_config_default.json> file

4 - Flash SoftDevice, Serial Bootloader, first application (examples/dfu) and Device Page in this order in every device

5 - Transfer the DFU archive over serial to one of the boards that then transmits the DFU archive in chunks to the boards in the vicinity.

I could follow the example, and we think the DFU chunks went through since we got the percentages on screen of the transfer and "Device programmed" in the end. The led's didn't start blinking though, and we would like to generate a DFU archive using the blinky example to check that.

We tried using nrfutil to generate a DFU archive like previously, but using the blinky hex file that Segger outputs, to the nRF5_SDK_15.2.0_9412b96/examples/peripheral/blinky/pca10056/blank/ses/Output/Release/Exe folder, but got an error that said ValueError: tobinarray: wrong value for size. We inspected the memory map of the DKs after programming the example DFU application using nRFConnect and in fact noticed something odd...

The Application part of the program on the DKs is huge compared to the blinky one. This leads us to think that we just cannot pick any random hex to transmit via DFUOTA.

What we would like to know is how to adapt an application to be able to be transfered using DFUOTA. We could not find anything about it in the documentation.

Also, what is included in a hex file that is compiled using segger? We normally use segger to compile and program the boards, so we didn't have to bother with that until now. Is the soft device included by default? Is it programmed separately? What about the bootloader?

[Hung Bui]

Hi Rmarques, 

Most likely it was the bug in our SDK v3.1 causing the issue. 

You can have a look here : https://devzone.nordicsemi.com/f/nordic-q-a/46950/problem-with-mesh-dfu

Especially the fix with optimal_bank_address()

However the bug should be solved in SDK v3.2. Could you give it a try ? 

[rmarques]

Did not work. I am now using Mesh SDK v3.2 and Nordic SDK 15.3.

In fact, now the LEDs start blinking but that might be just because I stopped using signature verification, after removing the public_key attribute from nrf5SDKforMeshv320src/tools/dfu/bootloader_config_default.json and removing the --key-file private_key.txt option from nrfutil dfu genpkg when generating the firmware archive.

The behaviour of the boards is not predictable either since after reprogramming everything from step 4, I was using /dev/ttyACM0 to test the DFUOTA in step 5 and it never worked. Tried using /dev/ttyACM1 and it worked... ONCE!

That time all 3 boards started blinking the 4 LEDs. I could not repeat the experiment though, despite having step 4 scripted to run over the 3 boards automatically, including generating the device page from the bootloader_config_default.json using the device_page_generator.py.

Is it possible I have a problem with the serial driver or some library misconfigured? I can always program step 4 but sometimes step 5 fails (most of the times) and sometimes it doesn't...