nRF52 SDK14.2 "ble_app_buttonless_dfu" example: What is the value written to the characteristic when entering the bootloader using nRF Connect application (Android).

Question

I am trying the buttonless DFU example from SDK14.2.0. I am not following the testing procedure mentioned at infocentre for SDK14.2. 
 Followed test procedure: 
 1. Erase device. 
 2. Upload softdevice v5.0.0 
 3. Upload bootloader_secure_ble bootloader. 
 4. Compile ble_app_buttonless_dfu example and generate a ZIP package. 
 5. Device advertising as DfuTarg . Connect and upload generated ZIP package using nRF Connect (Android). 
 6. Connect to Nordic_Buttonless . 
 7. Select: Secure DFU Service. 
 8. Enable N otification and click on Write Characteristic icon. 
 9. Prompt: "Enter Bootloader mode?" 
 10. Select: Yes 
 11. Device exits application, enters bootloader mode and advertises as DfuTarg . 
 
 The above procedure works absolutely fine. 
 Problem arises when I change the vendor specific UUID. 
 On doing so, all the steps from 1 to 8, mentioned above work fine, however, I do not get a prompt from step 9. This is expected as the nRF Connect application does not recognise the new UUID and service. 
 I have to manually enter the value to enable bootloader. 
 In SDK12.2.0, this value used to be 0x01 , however this value does not work for this version of SDK. 
 I have tried both 0x01 and 0xB1, but to no vain. 
 
 Can you please recreate this test and/or suggest me the exact value to be entered to enter bootloader mode

Bjørn Kvaale · Answer

Hi Rishi, 
 Quick question: are you using an nrf52 Dev Kit? 
 Just finished testing on my nrf 52 DK with a 52832 chip. I went through the exact same procedure as you did and got it working with both the nordic base uuid & a vendor specific UUID using SDK 14.2! 
 To get the vendor specific UUID, I used this online generator to generate the UUID. Then, I went into ble_dfu.h in the buttonless dfu app & wrote this code underneath the #define BLE_NORDIC_VENDOR_BASE_UUID. 
 /**@brief Test vendor-specific base UUID, 3fd64673-9a82-49c5-adaa-349a9faadece from
 https://www.uuidgenerator.net/
 */
#define BLE_VENDOR_SPECIFIC_BASE_UUID \
{{ \
 0xCE, 0xDE, 0xAA, 0x9F, 0x9A, 0x34, 0xAA, 0xAD, \
 0xC5, 0x49, 0x82, 0x9A, 0x73, 0x46, 0xD6, 0x3F \
}} 
 
 Then, in ble_dfu.c, I added a line under: ble_uuid128_t nordic_base_uuid = BLE_NORDIC_VENDOR_BASE_UUID; 
 where I defined the vendor_base_uuid: 
 ble_uuid128_t vendor_base_uuid = BLE_VENDOR_SPECIFIC_BASE_UUID; // added by BK 
 Lastly, I changed the code err_code = sd_ble_uuid_vs_add(&nordic_base_uuid, &m_dfu.uuid_type); 
 to: 
 err_code = sd_ble_uuid_vs_add(&vendor_base_uuid, &m_dfu.uuid_type); 
 
 I used the regular bootloader with private & public keys & followed the Nordic secure dfu blog post to get that set up. Should work with the debug bootloader too, but I have not tested this. 
 I then followed your steps 1-7 & on step 8 I press the button with the up & down arrows next to the unknown characteristic. A cross mark should appear on the button. This characteristic should have the same base UUID that you generated with the online calculator above. Then, I pressed the write button (the one with the upwards arrow) & wrote 0x01 to the characteristic & pressed send. 
 You should then notice that the DK enters bootloader mode because LEDs 1 & 3 start lighting up. I tested this using nrf connect for mobile on both Android & iPhone & both methods worked out of the box. 
 Hope that helps! Kind Regards, 
 Bjørn Kvaale