dual bank DFU is redundancy?

[loquat]

I try  dual bank DFU on nrf52832+SDK15.0.0.

After extract new image to dst_addr(run image_copy),

DFU run nrf_dfu_settings_write().

nrf_dfu_settings_write() is run, nrf_dfu_flash_erase() and nrf_dfu_flash_store().

When  happen 'RESET' between nrf_dfu_flash_erase() and nrf_dfu_flash_store() , DFU setting seem invalid.

Is there a way to avoid this?

[Bjørn Kvaale]

Are you building your own custom bootloader? Have you taken a look at the code in the secure_bootloader example in the latest sdk? If you want to do a dual bank dfu, I would take a look at how the example code does the dfu & base your bootloader on that code. The documentation at this link might also be helpful. Dual Bank DFU is mainly used as a fail safe so that if the firmware update fails, you can still boot your old application. If you do a single bank dfu, your old application will be erased. So if the DFU fails in a single bank dfu, you do not have a working application anymore. See the documentation I posted for more info regarding this.

[loquat]

I look at secure_bootloader(pca10040_ble).

Another words question,
When running nrf_dfu_settings_write().
1. old application information is in m_dfu_settings_buffer only?
2. nrf_dfu_flash_erase() and nrf_dfu_flash_store() run in order?
3. After nrf_dfu_flash_erase() run, where old application information remain?

[Bjørn Kvaale]

The nrf_dfu_settings_write() function writes the bootloader DFU settings to flash. The bootloader settings contains information about the current DFU process, in addition to application & firmware version numbers. 

1) The old bootloader settings application version information is located in the m_dfu_settings_buffer. This buffer gets updated with the new bootloader settings in the nrf_dfu_settings_write() function.

2) nrf_dfu_flash_erase() is executed before nrf_dfu_flash_store().

3) The bootloader settings (including application version information) are erased during the nrf_dfu_flash_erase() function.

If you want to know what happens with the application itself, take a look at this link.

[loquat]

If, betweeen nrf_dfu_flash_erase() and before nrf_dfu_flash_store(). reset happen.

Can bootloader run the new application ?
or
bootloader run the DFU operation ?

[run_ar]

The bootloader does not have a recovery feature in that sense. If the bootloader setting is blank or the crc fails (crc for bootloader setting to verify the write is correct) the bootloader will stay in dfu mode and wait for a new update.