DFU Verification Failure from Custom App

Question

I am writing my own DFU app for the nRF52832. I am using C# and .NET with Visual Studio. 
 For reasons I don't want to get into I can't use the Nordic SDK library with this project. 
 In a previous project I was able to write my own DFU process. I have copied that into this new project. 
 I have a .zip update file that contains the bootloader and app. This .zip file works fine when I use the nRF connect app and do the DFU process. 
 If I tried to use that same .zip file with my process it gets a EXT_ERROR_VERIFICATION_FAILED at the final step when I do the Execute operation. 
 I start by doing the Init download of 141 bytes. The checksum matches. 
 I then download the 107K binary data file in 4096 byte chunks. All chunk checksums match during the download. 
 At the end when I have transferred all the firmware I do the execute operation and the response is the extended error EXT_ERROR_VERIFICATION_FAILED. 
 Please give me some ideas about why this would happen. 
 Our bootloader and application are using SDK 15.3.0.

Tony · Accepted Answer

You can ignore all of this whole thread if you like. We found the problem. We found it after finally being able to get logging going in the bootloader. 
 We then ran the DFU using the nordic nRF Connect app. Then we took a log with ours. 
 For reasons related to how our app was doing things we found that we were only sending 178 bytes, but the nordic app was sending 180. 
 We got flash write failures when we only sent 178 bytes. I fixed that and now everything is working fine. 
 I never got any other errors to indicate this was the issue, however, so it would be nice if the bootloader or SDK would be able to either handle blocks != 180 bytes or give some error on the command channel that would have been caught indicating what was going on.

DFU Verification Failure from Custom App

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