Module starts advertising as dfuTarg if BLE disconnects during DFU

[SK]

Hello, 

I am using nRF52832 with SD v5.0.0 and SDK version 14.2 on a custom chip. 

I have implemented FOTA with buttonless DFU on my application and is working fine. 

However, i have a question:

Let's say i have an application with advertising name ADV1 and if in secure DFU mode, advertising name is DFUBOOT. Now it is advertising as ADV1 and i connect to it. I want to update the application now with ADV2 as advertising name.

Once the DFU process starts, in between, i disconnect the BLE and then reconnect again.

What i see is that module starts to advertise as DFUBOOT instead. Shouldn't it advertise as ADV1 only since DFU was not completed? Or the behavior i observe here is correct? 

My understanding is that once DFU starts, bootloader will store the incoming image to a different memory and after post validation only it will overwrite the previous application image with a new one. (DUAL BANK UPDATE)

Please let me know if my understanding is wrong here and if there is anything i should be doing so that even if DFU fails, it should start to advertise with the exisiting application.

Thanks a lot in advance! SK

[Vidar Berg]

Hi,

Once the DFU process starts, in between, i disconnect the BLE and then reconnect again.

What i see is that module starts to advertise as DFUBOOT instead. Shouldn't it advertise as ADV1 only since DFU was not completed? Or the behavior i observe here is correct? 

 It sounds like the correct behavior - the device is still in DFU mode waiting for the DFU controller to re-connect and finish the application update to ADV2.  However, the bootloader has an inactivity timer with a timeout of 2 minutes (default) so I would expect it to start ADV1 if you don't reconnect and just let it time out. 

My understanding is that once DFU starts, bootloader will store the incoming image to a different memory and after post validation only it will overwrite the previous application image with a new one. (DUAL BANK UPDATE)

 Yes, that is correct. 

[SK]

Hi Vidar Berg, 

Thanks a lot! Tested and it works exactly like you said. I wonder if we can make inactivity timer to zero? So it starts advertising the sec there is an incomplete DFU process. 

[SK]

Okay, so minimum that can be is 100 ms. Does it also mean that if there is no application, it will just advertise for 100 ms and turn off? 

[Vidar Berg]

The bootloader will always reset when the inactivity timer times out and on the following startup, it will either enter DFU mode again or boot the application. 

[SK]

okay i changed NRF_DFU_POST_SD_BL_TIMEOUT_MS  and NRF_DFU_INACTIVITY_TIMEOUT_MS to 100 ms as it is the least possible value suggested. 

Now when i do DFU, it disconnects automatically with DFU operation failed and starts to advertise with the existing application. 

Does that mean this timer also accounts to how much time it takes to start the DFU process? Because in that case, setting 100 ms is not possible at all.