BLE DFU Dual-Bank : Is the copy process, which follows the update process, safe?

[Xavier Waselle]

I'm currently on a question for which the documentation here can't help me.

If I'm correct, the Dual-Bank Update allows to retain a safe copy of the old firmware image until the new firmware image has been completely validate aside the old one when processing the post-validation of the DFU Process. If something goes wrong during the transfer, the bootloader will check the bootloader_settings and restart the transfer where it has been left. Then, if the new firmware image can be activated, it is copied from bank 1 to bank 0.

So, if there is a problem, like a cut-off, during the transfer, all will be safe. The DFU Process will restart and the old firmware image is always in the flash in bank 0.

However, what is going if there is a problem, like a cut-off, during the copy from bank 1 to bank 0 of the new firmware image ? (second step in the scheme above)

PS : this post didn't help me either.

[Andy]

The bootloader still knows that there is a valid application in bank 1. Bank 1 isn't "cleared" until the application has been copied to bank 0 successfully, i.e. if the copy process fails due to reset or whatever, the bootloader will try to copy the application again on the next boot.

[Xavier Waselle]

Ok but is it always the case if the size of new firmware image is bigger than the previous one?

I mean how is it proceed exactly because, as far as I know, we will copy the beginning of the new application over all the old application but the old bank 0 will not fit to the new application. Am I right? So, where will be copied the end of the new application image ? Over the beginning of the new one already copied ? If it's the case, how the bootloader can know it ?

[Andy]

I'm not sure if I understand what your question is. It doesn't matter if the new firmware is smaller or bigger, what matters is if the new firmware fits in bank 1.

All of this is pretty well documented: Take a look here.

[Xavier Waselle]

The documentation didn't help me because it does not explain in details the copy process but I got my answer after looking in the code in image_copy().

When processing the copy, the bootloader divides the new app in pages and copies them one by one and save the store progress in flash on every successful chunk write.