https://devzone.nordicsemi.com/f/nordic-q-a/58754/usb-secure-bootloader-behaviourTo the kind attention of Nordic support team, I have got in here two pictures of flash. The first one it is after installing bootloader and settings, softdevice and application. The second one it is after having done a dfu update of softdevice anden-USTelligent Community 13Fri, 06 Mar 2020 15:24:13 GMThttps://devzone.nordicsemi.com/thread/238573?ContentTypeID=1Fri, 06 Mar 2020 15:24:13 GMT137ad170-7792-4731-bb38-c0d22fbe4515:67fa0951-9f85-4713-a36e-b9f6b7bec3b8astella<p>Thank you for your kindness.</p><div style="clear:both;"></div>https://devzone.nordicsemi.com/thread/238568?ContentTypeID=1Fri, 06 Mar 2020 14:59:14 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f989bdb2-84ae-4239-9778-b5dcc0921b08Einar Thorsrud<p>Hi,&nbsp;</p> <p></p> [quote user=""]<p></p><p>I was wandering if the application copy starting at 0x61000, and created after a usb dfu updating is a safety copy made by bootloader</p><p>to be able to recover in case of power failure.</p><p></p>[/quote] <p></p> <p>Yes, it is. The bootloader will temporarily store the new application and copy it in place after it has successfully been received and validated (aka dual banking).</p> <p></p> [quote user=""]<p></p><p>Also I wanted ask if, being thins like that, we always have to leave free space in flash whose dimension</p><p>is at least application size, in order to allow the copy process? What happens shouldn&#39;t be enough free space in flash memory? Does dfu fails?</p><p></p>[/quote] <p></p> <p>Dual banking of application updated is optional (but can be configured to be mandatory). So if there is no space for dual bank updates, the application would be deleted before starting the update process, so that no additional flash space is needed. This has the downside that a device will stay in DFU mode if an update is not completed, instead of going back to normal operation. This is not a big issue for most products though.</p><div style="clear:both;"></div>