New application doesn't run after secure DFU process reaches 100%

Question

Hi to everyone! 
 I'm following this guide to learn how to use secure DFU on a nRF52832DK board. 
 All steps have been done successfully, or I think so, until I reach the D4 step where the new program has to start automatically after DFU process, but it never runs. 
 Instead, the LED 3 lights up and If I press the button 4, the LED 1 also lights up and I can resend another application over DFU. So I think the board is still in the bootloader. 
 Indeed, I have some cuestions related to this: 
 
 
 BLE Secure DFU example is only a
boot loader or it also has an
application? 
 
 
 Depending on the above answer, if it
is only a boot loader, do I have to
program an application before doing
the DFU proccess? 
 
 
 The application, that will be
written after DFU proccess, must use
SoftDevice? (For my test, I upload
my own blinky program. It works well
when I flash the board directly
through USB. But it doesn't use
SoftDevice at all). 
 
 
 Thanks in advance!

Bjørn Kvaale · Accepted Answer

I tried your way with the precompiled hex file, but that didn't work. The reason it doesn't work is because the precompiled hex file has the softdevice included, but in the secure DFU blog post you are looking at, you only want to update the application (not the softdevice too). Try building the blinky example using Keil instead (like it says in step C1 ). The hex file built by Keil in the _build folder does not include the softdevice. You can check this in nrfgostudio by uploading the precompiled hex file found in the hex folder as an application and seeing that there is a softdevice & application section in memory. If you program the hex file built by Keil, the softdevice will not be in memory. 
 Like you said previously, you get errors if you try to create a zip file by using the precompiled blinky_pca10040.hex file. I am pretty sure you are doing everything else correctly. So essentially just follow the blog post and build your application using Keil & not using the precompiled hex files. Hope that helps!

New application doesn't run after secure DFU process reaches 100%

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