DFU from external Flash - nRF Connect SDK - swap

[Lorenzo Amicucci]

Hi

I would like a clarification when performing DFU from external flash. 
This is applicable to both nRF52 and nRF91, I guess, as long as nRF Connect SDK and MCUboot is used.
In my case, I am more interested in nRF9160 case, when you want to do FOTA of the Application Core  (M33)  from external flash. 

Here we say that "You can use the external flash memory as the storage partition for the secondary slot" . https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/nrf/ug_bootloader_external_flash.html 

This is good: I can use the flash in the M33 (1MB - MCUboot) for the application, but for DFU, I can use the external flash as secondary slot.

However, In the documentation, I cannot find the following information: 

What is exactly happening when we swap the two slots? Does the image from external flash go to the primary slot on the M33 and the image from the M33 goes to the secondary slot on the external flash? Or we just overwrite the primary slot in the m33 with the image from the external flash, but we lose the old image (hence preventing fall back if the new image is corrupted?)

Thanks

BR
LA

[Håkon Alseth]

Hi Lorenzo,

 

The mcuboot documentation will cover most of their questions:

https://developer.nordicsemi.com/nRF_Connect_SDK/doc/latest/mcuboot/design.html#image-slots

 

They effectively swap place, then the new image will be executed from primary slot and once "boot_write_img_confirmed()" is called, it will be verified.

If this function is not called, then the image will be reverted upon reset (ie. back to old image).

 

Kind regards,

Håkon

[Lorenzo Amicucci]

Ok, thanks.
So basically you confirm that we can go back to the old image, also when on external flash. 

[Håkon Alseth]

Happy to help out.

Lorenzo Amicucci said:

So basically you confirm that we can go back to the old image, also when on external flash. 

yes, you can.

 

Kind regards,

Håkon 

[Lorenzo Amicucci]

ok, we can close it. Can you make it public?

Thanks

[Håkon Alseth]

Only you have the permission to convert a case from private to public.

 

Kind regards,

Håkon