Solved DFU disconnected problem for Android 10 but results in increase in GATT Error

[Mxoh]

Hi there!

We faced the problem of not being able to perform Legacy DFU with Android 10 and newer iOS devices and have since applied the fix. However, since doing so we observed that there are more instances of GATT error. We have been monitoring DFU failures in our app and you can see a trend after applying the fix at around mid/end Aug, the DFU disconnected problem users decreased but GATT error users increased significantly. 

[Hung Bui]

Hi Mxoh, 

Could you let me now which exact fix you used regarding legacy DFU and Android 10 & iOS ?

Have you managed to reproduce the issue inhouse ? or you have only received the report from the customers ? If you can reproduce the issue I would suggest to capture a sniffer trace so we can have more understanding of the issue. 

[Mxoh]

Let me check with my developers and get back to you. I have been actively monitoring DFU problems faced by our customers as firmware update of their BT device is a key functionality of our iOS and Android app. I was surprised to see that GATT error shot up by so much since we fixed the legacy DFU highlighted here through the latest Android and iOS DFU library: https://devzone.nordicsemi.com/f/nordic-q-a/60658/not-able-to-perform-legacy-dfu-with-android-10-and-ios 

[Mxoh]

Hey Hung Bui

I just checked with my Android developer and we are using this library: https://github.com/NordicSemiconductor/Android-DFU-Library. We downloaded and added it into our app changing one line in the file LegacyButtonlessDfuImpl.java at line 198 to restartService(newIntent, /* scan only for SDK 6.1, see Pull request #45 */ true); to solve the problem of Samsung + Android 10 DFU disconnected problem. 

We haven't been able to replicate the issue in-house as we don't know what model or phones are showing up with GATT Error. Would it be helpful if we provided you with the zipped file of the DFU library? 

[Hung Bui]

Hi Mxoh, 
So in the fix you did, you forced scanning for different address of the advertiser ? 
I'm not 100% sure it would fix the issue described in here: https://devzone.nordicsemi.com/f/nordic-q-a/60658/not-able-to-perform-legacy-dfu-with-android-10-and-ios
The issue described in the case was about that the DFU bootloader may advertise in directed advertising mode when the central device already changed the address. By having the address changed the central won't be able to connect to the DFU bootloader. (even if you try to scan for the advertising packet, the directed adveritising will not show up if the target address doesn't match)

The best solution for this is to modify the DFU bootloader to not advertising in directed advertising and use the normal advertising instead. Or to bond to the central to get the IRK, but I guess it's not the case here. 

We would need to have the sniffer trace and maybe DFU log on both the phone side and the nRF52 side when the GATT error happens. 

[Mxoh]

This workaround was suggested because we had to modify firmware to delete dfu_app_peer_data_set so as to fix the DFU disconnected problem. More information on why we did this workaround is explained here: https://devzone.nordicsemi.com/f/nordic-q-a/66015/how-can-ios-dfu-library-v4-8-0-work-with-the-sdk11-workaround-delete-dfu_app_peer_data_set-in-application-of-firmware/272714#272714

Let me see if I can get the other information for you.