DFU CRC check workaround for J-Link debugging

Question

Common situation: 
 We have flashed dfu bootloader, and firmware uploaded into Flash via DFU. In this situation, DFU settings page contains correct CRC value for existing application. But if we make any changes in code and upload new version with J-Link, bootloader never start application due to wrong CRC checking. 
 So, my suggestion to add two lines in nrf_dfu_utils.c function nrf_dfu_app_is_valid() 
 if (crc != s_dfu_settings.bank_0.image_crc)
 {
 // CRC does not match with what is stored.
 NRF_LOG_DEBUG("Return false in CRC");
#ifndef NRF_DFU_DEBUG_VERSION
 return false;
#endif
 }
 }

 NRF_LOG_DEBUG("Return true. App was valid"); 
 This change will affect only debug version of bootloader and we still have information about CRC in log

tesc · Accepted Answer

Hi, 
 The way this is currently done is that for the debug version of the DFU bootloader (which is a separate project from the non-debug version) the CRC is set to 0 which leads to checking the CRC of the application being skipped. Intended use is to use the debug version of the bootloader during development, which lets you change the application without recalculating CRC every time. 
 I do see, however, that your suggestion may have some advantages, and as always I have registered the suggestion in our internal issue tracker. Feedback from customers is always highly appreciated! 
 Of course one can always do as you suggest manually, and add an #ifndef checking for a debug flag around the "return false;". 
 Regards, Terje

DFU CRC check workaround for J-Link debugging

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