I use iOS nRF Connect APP to test DFU. But it failed with writing is not permitted.
The following is log message of nRF52832 device.
00> <info> app: Inside main
00>
00> <debug> app: In nrf_bootloader_init
00>
00> <debug> nrf_dfu_settings: Calling nrf_dfu_settings_init()...
00>
00> <debug> nrf_dfu_flash: Initializing nrf_fstorage_nvmc backend.
00>
00> <debug> nrf_dfu_settings: Using settings page.
00>
00> <debug> nrf_dfu_settings: Copying forbidden parts from backup page.
00>
00> <info> nrf_dfu_settings: Old settings page detected. Upgrading info.
00>
00> <debug> nrf_dfu_settings: Writing settings...
00>
00> <debug> nrf_dfu_settings: Erasing old settings at: 0x0007F000
00>
00> <debug> nrf_dfu_flash: nrf_fstorage_erase(addr=0x0x0007F000, len=1 pages), queue usage: 0
00>
00> <debug> nrf_dfu_flash: Flash erase success: addr=0x0007F000, pending 0
00>
00> <debug> nrf_dfu_flash: nrf_fstorage_write(addr=0x0007F000, src=0x20006F38, len=896 bytes), queue usage: 1
00>
00> <debug> nrf_dfu_flash: Flash write success: addr=0x0007F000, pending 0
00>
00> <info> nrf_dfu_settings: Backing up settings page to address 0x7E000.
00>
00> <debug> nrf_dfu_settings: Writing settings...
00>
00> <debug> nrf_dfu_settings: Erasing old settings at: 0x0007E000
00>
00> <debug> nrf_dfu_flash: nrf_fstorage_erase(addr=0x0x0007E000, len=1 pages), queue usage: 1
00>
00> <debug> nrf_dfu_flash: Flash erase success: addr=0x0007E000, pending 0
00>
00> <debug> nrf_dfu_flash: nrf_fstorage_write(addr=0x0007E000, src=0x200072B8, len=896 bytes), queue usage: 1
00>
00> <debug> nrf_dfu_flash: Flash write success: addr=0x0007E000, pending 0
00>
00> <debug> app: Enter nrf_bootloader_fw_activate
00>
00> <info> app: No firmware to activate.
00>
00> <debug> app: crc_on_valid_app_required() return 0x1
00>
00>
00> <debug> app: App is valid
00>
00> <info> nrf_dfu_settings: Backing up settings page to address 0x7E000.
00>
00> <debug> nrf_dfu_settings: Destination settings are identical to source, write not needed. Skipping.
00>
00> <debug> app: Running nrf_bootloader_app_start with address: 0x00001000
00>
00> <debug> app: Disabling interrupts. NVIC->ICER[0]: 0x0
