New firmware images can be transferred over two different transport protocols: BLE or using serial wire (HCI/UART). In both cases, the DFU bank handling is responsible for writing received data packets to flash memory.
The BLE transport uses a BLE service for data transfer (see BLE DFU Service) and relies on the S13x or S332 SoftDevice.
The following figure shows a schematic overview of the DFU process using BLE:
Alternatively, new images can be transferred using HCI over UART (serial transport). The HCI transport layer increases robustness of the transfer. See UART_HCI PHY (reliable UART) for more information about UART_HCI, and Serial (HCI) packet format for more information about the packet format.
Serial transport does not use a SoftDevice. However, you must install a SoftDevice on your device to correctly create the Master Boot Record.
The following figure shows a schematic overview of the DFU process using with UART.
