Downloading combos using DFU

[DBT]

I'm trying out DFU functionality using nRF52840-PreviewDK and UART transport

On this page there is a table listing all the different combinations that can be downloaded via DFU

https://devzone.nordicsemi.com/nordic/nordic-blog/b/blog/posts/getting-started-with-nordics-secure-dfu-bootloader

I've tried all the combinations except BL+APP.

Does the "Create two .zip packages instead" just mean to do a download of BL then a download of APP (not really a combo)?

Should I do BL then APP or APP then BL?  Does it matter?  Are there some cases where you would want to do one order vs another?

Regarding the note "SD must be of the same Major Version"

If you need to update the SD to a different major version does this just mean that you need to update the APP and BL at the same time in a combo?

So you'd do this with a BL+SD+APP combo download?

[Edvin]

Hello,

This table is mostly directed to the BLE bootloader. Hence the notes: "SD must be of the same Major Version". The reason for this is that the BLE bootloader uses the softdevice to get the new application images. If the bootloader suddenly receives a new softdevice with a difference major version, the API may have changed, and the bootloader can't use the softdevice properly, and hence can't receive new updates. That would lead to a bricked device. 

BL + APP: Do bootloader first, and then app, because the bootloader has to verify the app that is received. On every bootup, the bootloader will verify the CRC of the application, and hence, the app should be transferred via that bootloader. 

If you use a BLE bootloader and need to update major version of the softdevice, you also need to update the bootloader that uses the same SD version that you want to update to. If you use a serial bootloader, this requirement is not so strict. Have you tested? I am not sure if the check of the init packet in the DFU image will be rejected if it uses a different version.

 

So you'd do this with a BL+SD+APP combo download?

 Yes.

Best regards,

Edvin

[DBT]

Thanks. I haven't tested changing the major version of softdevice yet.  I'll try that later.