Why there are multiple resets during firmware upgrade?

[Engineer01]

Why there are multiple resets after post validation, firmware activation, etc in firmware update process? Can it not be handled sequentially without resets?

[Amanda Hsieh]

Hi, 

Are you using nRF5 SDK and updating with SD? If so, see the DFU package combinations Note.4:

⁴The SD (+ BL) + APP update is done with two consecutive connections, unless a custom bootloader is used. First the SD (+ BL) is updated, then the bootloader will disconnect and the (new) BL will start advertising. Then the second connection to the bootloader will update the APP.

Regards,
Amanda