A bootloader may be used to handle in-system update procedures.
The bootloader has full access to the SoftDevice API and can be implemented like any application that uses the SoftDevice. In particular, the bootloader can make use of the SoftDevice API for BLE communication.
The bootloader is supported in the SoftDevice architecture by using a configurable base address for the bootloader in the application Flash Region. The base address is configured by setting the UICR.BOOTLOADERADDR register. The bootloader is responsible for determining the start address of the application. It uses sd_softdevice_vector_table_base_set(uint32_t address) to tell the SoftDevice where the application starts.
The bootloader is also responsible for keeping track of, and verifying the integrity of the SoftDevice. If an unexpected reset occurs during an update of the SoftDevice, it is the responsibility of the bootloader to detect this and resume the update procedure.