https://devzone.nordicsemi.com/f/nordic-q-a/21700/how-nrf-bootloader-finds-which-images-is-flashing-currentlyHi, I want know how nrf51822 bootloader finds images type(means weather it is softdevice,bootloader,app) when we pass an image to bootloader for update. And also how bootloader comes to know weather an application is properly flash or not.en-USTelligent Community 13Fri, 28 Apr 2017 06:53:49 GMThttps://devzone.nordicsemi.com/thread/85245?ContentTypeID=1Fri, 28 Apr 2017 06:53:49 GMT137ad170-7792-4731-bb38-c0d22fbe4515:f81e31c4-670d-4d44-9889-4fd89f0d7f63bjorn-spockeli<p>Hi Sudhan,</p> <p>you specify the image type when you create the firmware images (.zip) files , see <a href="http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.sdk5.v11.0.0/bledfu_example_image.html?cp=4_0_3_4_2_3_1_2">this</a> page if you&#39;re using our Legacy Bootloader( SDK v11.0.0 or older) or <a href="http://infocenter.nordicsemi.com/topic/com.nordic.infocenter.tools/dita/tools/nrfutil/nrfutil_pkg.html">this</a> page if you&#39;re using the Secure Bootloader( SDK v12.0.0 and later).</p> <p>Both bootloaders will verify that the firmware image has been received correctly, i.e. perform a CRC check of the image and compare it to the CRC calculated when the image file was created. After it has verified that the image is complete the bootloader will copy the image from (Bank 1) into the application region( Bank 0) and then compare Bank0 and Bank 1 to verify that the copy operation was successful. If not it will erase Bank 0 and perform the copy operation again.</p> <p>Best regards Bjørn</p><div style="clear:both;"></div>