dfu removes bonds

Question

Hello, 
 
 I am using secure dfu with bonds (SDKv15.3, Segger, nrF52832), it works fine however after each dfu (application only) I lose the bond information. 
 
 I have search about it and found that there are several variables that can affect to it, I think I checked all of them but the problem still remains: 
 1-I use nRF Toolbox from Android phone and I enabled the "keep bonds" option on the settings. Can you btw tell me what is doing exactly this option and how is this setting is transfered to the secure dfu code to remove or not the bonds? 
 2-The sdk_config.h on the secure download has NRF_DFU_APP_DATA_AREA_SIZE set to 12288 (I think is correct to match FDS 3*4*1024) 
 3-FDS on the application side (based on heart rate example) has FDS_VIRTUAL_PAGES = 3, FDS_VIRTUAL_PAGE_SIZE = 1024, where I think stores the bonds. 
 According to comment on sdk_config.h it is same size as 12288: 
 // <i> The total amount of flash memory that is used by FDS amounts to @ref FDS_VIRTUAL_PAGES * @ref FDS_VIRTUAL_PAGE_SIZE * 4 bytes. 
 
 To me knowledge all seems to be fine, but .... why I after dfu the phone and board cannot connect? 
 To bypass the problem I remove bonds on the board and phone and connect them after each dfu, then everything seems to work fine... till the next dfu. 
 
 Thanks, 
 
 Carlos

bjorn-spockeli · Accepted Answer

Hi Carlos, 
 Looking at the sniffer trace and the last connection I cannot see anything wrong with regards to the reencryption using the bonding data( i.e. stored encryption key). The link layer packets(i.e. LL_ENC_REQ/RSP, LL_START_ENC_REQ/RSP) are all send in the correct order and the parameters look good. 
 
 So the bonding data must be preserved during the DFU otherwise you should have gotten a LL_REJECT_IND or LL_REJECT_EXT_IND packet in return. 
 The sniffer trace does not show any LL activity nor ATT activity after the link is encrypted. If the nRF device was bonded with the Android device, then it should have cached the GATT table of the application. However, it could be that you simply have to update the GATT attribute 
 Does the DFU update increase or modify the GATT table of the application compared to the application that was replaced? OItherwise,the GATT attribute table handles should be the same as before the DFU. 
 Can you check if the NRF_SDH_BLE_SERVICE_CHANGED define in sdk_config.h is set in the bootloader project? Could you also check if this is set in the applicaiton as well? 
 We do have a "refresh device cache" feature in nRF Connect. Connect to the device, then press the three vertical dots in the upper-right corner and then press "R efresh device cache". Does the Android device perform a new service discovery and display the services and characteristics after doing this? 
 Best regards 
 Bjørn

dfu removes bonds

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