Android & Dual mode Bluetooth device: Custom BLE service not found when paired to BR/EDR (Classic)

1
votes

I've built a dual mode Bluetooth device using the BT 121 from Silicon Labs. The device implements SPP over the classic connection. The device name of the classic node is "XYZ Classic". It also implements a custom service (128-bit UUID) in BLE. The device name of the BLE node is "XYZ_BLE". Both nodes have the same MAC address.

When pairing under 'Bluetooth' settings, sometimes I will see 'XYZ Classic' and sometimes I will see 'XYZ_BLE'. It seems random which one it will pair to but many Android devices I've tested have a tendency to want to pair to the classic node. After pairing, a connection over classic/SPP ALWAYS works. However, I can only connect to the custom service if paired to the BLE node. If paired to classic I can see non-custom BLE services but not my custom service. To summarize:

Function     Classic Pairing     BLE Pairing
Spp          Works               Works
Cust BLE     Doesn't Work        Works

When I pair in code (Android) the problem also happens despite the fact that I search for the devices named 'XYZ_BLE' and then pair to the device returned. I've looked but I can't see a way to force Android to pair to the BLE node.

My only workaround thus far has been to modify my BT 121 firmware to not allow bonding in classic mode. This is not an ideal solution has any Bluetooth Classic only devices will not be able to bond with my device (In reality this might not be too big of a problem but I have one tablet in my possession that only has Bluetooth Classic).

It should be noted that I've used 'BLE Scanner' from the play store to verify that my custom service works/doesn't work depending on the pairing mode. In other words, it's not just my code. :)

So, does anybody have any ideas on how to force Android to pair to the BLE node?

1
androidbluetoothbluetooth-lowenergypairing

1 Answers

0
votes

I see similar issues. Some hints:

Android behaviour differs dependent on the bit flags you set in the BLE advertising. There is for example a bit called "no br/edr support" or so. There are also bits telling explicitly that br/edr dual role is supported.

Also ble pairing may be enforced if you access a characteristic which returns a "not authenticated error" from a ble app. At least on iohone, the os will initiate the ble pairing automatically.