DFU upgrade bootloader and softdevice use single bank

[MR.liu]

I want achieve DFU upgrade bootloader and softdevice use single bank,my SDK is 9.0.0,is it possible?What should i do?

[bjorn-spockeli]

Yes, bootloader and Softdevice updates will always be updated using the dual-bank approach, eventhough you're using a single bank bootloader. The bootloader will not erase the old SoftDevice or bootloader untill the new image has been correctly received and its integrity checked. A single bank bootloader will only be singlebank for application updates, i.e. it will erase the old application to make rrom for the new appliaction.

However, keep in mind that the application will be erased when performing a SoftDevice + Bootloader update so you have to DFU in the application after the SD+BL update.

[MR.liu]

As the figure above,single bank updata application like this ,Just less replace existing images,Why can't use for update bootloader and Softdevice?