Trouble finding characteristics using android nRF toolbox, while the nRF Connect android app finds it ok

[desnyki]

Okay so the issue is a little more complicated than this.

Phones used for testing were htc m8 (android 6.0) and lg g5 (android 7.0).

Ble chip running on a linux OS using BlueZ stack.

I've modified two nRF toolbox apps to test the problem. The first one is BMP that uses a static reference to the BLEManager class, and the CSC which runs the BLEManager as a service. The behaviour is the same on both apps. My modifications consisted of:

1. Added my custom UUID to the ble scan filter.
2. Added a log that will print available services in onServicesDiscovered() callback.

Now the procedure and observations:

After resetting ble chip, and all app settings.

Step 1

1. Start nRF toolbox app and select bmp or csc app (with modified UUIDs by me). Run BLE scan with the service filter. The device is found.
2. Connect to the device and initiate the service discovery
3. print all services in onServicesDiscovered().
4. The primary service used in the filter is not displayed in the log.

Note: I have tried this with multiple connections tries, multiple discoverServices calls including using the hidden android ble refresh() method. Results are the same.

Step 2

1. Run nRF android app downloaded from the google store.
2. Connect to BLE chip
3. The service is instantly found.

Note: Same can be achieved running boilerplate BLE code on an iOS device.

Step 3

1. Disconnect from the device in the nRF android app and go back to the nRF toolbox app.
2. Repeat step 1
3. Now the service is displayed in the list of available services and can be used for communication.

Observations:

The service used to filter the scanned devices works, but then that service is not displayed in the onServicesDiscovered() until we run the nRF Connect Android app. I'm having trouble coming up with any reason for this. What is the nRF Connect app doing differently?

[desnyki]

I tried clearing the device cache, but that didn't turn out to be the issue. After further investigation on the hardware side the BlueZ chip would go into BR / EDR mode. This allowed for a successful GATT connection on the Android side, but the services did not exist in onServicesDiscovered. In order for the services to show up, the connection had to explicitly specify a BLE connection.

NRFToolbox connection code:

device.getDevice().connectGatt(applicationContext, false, mGattCallback);

The fix:

device.getDevice().connectGatt(applicationContext, false, mGattCallback, BluetoothDevice.TRANSPORT_LE);

Note: this method call requires Android API 23.

[Aleksander Nowakowski]

You may call this method in previous APIs as well, since 19 or 20, afair, just using reflections as it's hidden with @hide.

[Aleksander Nowakowski]

We will have it fix on nRF Toolbox soon. Thanks for pointing it out.