APP 'nRF Connect' can't connect to nRF52832 directly when turn on bluetooth after turn off it

[kenxie]

Hi! We use nrf52832 for product development. The SDK version we use is nRF5_SDK_15.3.0_59ac345, the software device version is s132, and the APP for debugging is "nRF Connect".

The current problems are as follows:

1.When using APP to scan and connect to nRF52832, if we click APP 'disconnect' button to disconnect from nRF52832 and then click the APP 'connect' button to connect to nrf52832, App can connect to nrf52832 normally;

2.When using APP to scan and connect to nRF52832, if we turn off bluetooth(App will automatically disconnect from nrf52832) and then turn on it, then click the APP 'connect' button to connect to nRF52832 directly(don't use scan button first), APP can be connected normally on some Android phones(like HTC one(android 6.0)), but not others(like honor9 and mi8(android 9.0));

3. When using APP to scan and connect to CC2541(from TI), the above two operations(1,2) can be connected to the app normally.

So, can someone help me answer this question？

[haakonsh]

What exactly is the problem here?

[kenxie]

the problem is When using 'nRF Connect' APP to scan and connect to nRF52832, then we turn off bluetooth and turn on it again, the APP can't connect to nRF52832 directly by click the 'connect' button.The operation steps are as follows：

step1: scan and connect to "RG-TEST";

step2: we can see that App is already connected to the device；

step3: then we turn off the bluetooth, we can see the phenomenon as shown in step 4;

step4: bluetooth has been turned off;

step5: next from step 4, we turn on the bluetooth and then click 'connect' button to connect to device, we can see the  phenomenon as shown in step 6;

step6: the App can't re-connect to device!!!!!

NOTE: TI's IC(like CC2541, CC2640) can be connected to the device with the above operations.

 So, what's the problem？Is there a problem with Nordic's own software or protocol stack? Or any other problem?

Can you help me？

[haakonsh]

Can you you "forget" the device by clicking the 'X' to the right of the RG-TEST name, and then scan and connect to it? 

[kenxie]

yes!!!  And at this time, it also can be scanned and connected with other mobile phones.

[haakonsh]

Then I think the issue is that the android phone has stored the pairing information (bonding), whereas the nRF52 has not. The android phone tries to connect to the nRF device with its stored pairing information but it fails because the nRF52 does not have the required paring information. 

See Peer Manager and Peer Manager API docs on how to enable bonding. 

[kenxie]

OK. If, as you said, but we can still connect directly(not need to pair) on Android 6.0, , how to explain this？

Can you do the experiment according to the steps I said? It should be possible to help you solve this problem better.

Thank you!!!

[haakonsh]

I suggest you take a sniffer log when you connect to the nRF device, and when it fails to connect again.