Device goes into DFU after adding FOTA over Bluetooth

[coolerkid]

I added FOTA over Bluetooth to my NRF52840 application. Everything works, I can update the application over bluetooth and it runs properly, but after updating if I unplug the dongle and plug it back in the device starts up in DFU mode instead of just starting up my application normally. Any idea why this would occur? Thanks 

[Vidar Berg]

Hello, 

Is this DFU mode (called serial recovery mode in MCUboot) in the nRF5 SDK bootloader that comes pre-programmed on the nRF52840 dongle, or in MCUboot? The only times the pre-programmed bootloader should enter DFU mode are if no valid application is present, or if the PINRESET bit is set in the POWER->RESETREAS register. And are you seeing this on more than one board?

Driving any of these pins low on the nrf52840 dongle will cause the bootloader to enter dfu mode (indicated by red LED) :

Ref. https://docs.nordicsemi.com/bundle/ug_nrf52840_dongle/page/UG/nrf52840_Dongle/hw_button_led.html

Best regards,

Vidar

[coolerkid]

After I flash it over Bluetooth my application works fine the first time, and I can confirm it's running the updated application, but once I unplug and plug it back in LED2 is flashing. If I open Programmer I see the device show up as Open DFU Bootloader and the contents of the device shows the application still there. Usually I have to press the reset button to get into this mode, but after flashing over Bluetooth it remains in this mode.

Could there be a condition where the application were able to run a first time but then when disconnecting it and reconnecting it the application isn't considered valid? I have tried calling boot_write_img_confirmed() on startup, but that did not fix it.

Thanks!

[coolerkid]

I compiled and flashed the open bootloader (open_bootloader/pca10056_usb_debug), but now I am unable to put it into DFU to install my firmware. I'm also not getting any logging. I'm kind of lost now what to do next. Thanks 

[Vidar Berg]

DFU will be on this USB port that is connected to the nrf USB: 

Did you connect to this? Also, is the goal to use the nRF52840 Dongle in your final solution? If not, I do not see any advantage of including this bootloader in addition to MCUBoot and would recommend to just use the latter.

[coolerkid]

Ok this is where I'm confused. I thought that when I pushed my app with MCUBOOT enabled, that MCUBOOT became the primary boot loader. After reading your response I believed that you were saying that there was a pre-bootloader on the Nordic Dongle that's different than the one on the DK and I had to load that version on the DK to be able to replicate the issue I'm having with the dongle? 

Yes I'm using that port to flash the device. 

Thanks 

[Vidar Berg]

Yes correct, so the dongle comes pre-programmed with this open_bootloader bootloader which can't be overwritten unless you connect an external debug probe to the dongle. For more details about this, please see the  nRF52840 Dongle Programming Tutorial . 

[coolerkid]

I don't understand what you mean when you say "If not, I do not see any advantage of including this bootloader in addition to MCUBoot and would recommend to just use the latter."

I take this to mean that I should only use MCUBoot and not the default bootloader, but how is that possible if this cannot be overwritten in the dongle?

I've read every article I could find on the bootloader and FOTA but I'm still lost what I need to do next to try and debug the situation I'm facing.

Thanks. 

[Vidar Berg]

coolerkid said:

take this to mean that I should only use MCUBoot and not the default bootloader, but how is that possible if this cannot be overwritten in the dongle?

Correct, but as mentioned in my previous reply you can overwrite it with a debugger. Also this is only relevant if your project uses the nRF52840 Dongle as it is the only device (at least from us) that comes pre-programmed with this bootloader. Loose nRF52840 ICs are shipped empty and require initial programming through the debug interface.

The nRF52840 Dongle is not intended for FW development or for use in a final product and the main if not only reason you might want to have *both* MCUBoot and the Open Bootloader programmed on the dongle is if you need to support Zephyr/NCS DFU, but don't have the option of overwriting the existing bootloader using an external debug probe. 

[coolerkid]

Our intent is to use a dongle from one of the companies where we can white label them for resale, instead of building our own because it has everything we need already.  I'm not sure if we will be having the manufacture flash these for us with our firmware or if we're going to do it ourselves, but if we do we'll only be able to flash it over USB so we likely wont have the option to write over the bootloader. 

So how can we debug this issue if it's working on the DK with the open bootloader, but not on the actual dongles we are trying to use? Can these dongles for sure support FOTA over BT?

Thanks

[Vidar Berg]

Thanks for the clarification. Perhaps it would be better to work with dongles from those companies then as they may ship with a different bootloader. The nRF52840 dongle is for example not FCC certified and may not be resold in markets requiring this.

coolerkid said:

So how can we debug this issue if it's working on the DK with the open bootloader

Did your program the open bootloader + MBR and where you able to upload your application through the nRF USB?  

coolerkid said:

Can these dongles for sure support FOTA over BT?

Yes.