Android BLE Connection time interval

Question

I am developing a BLE application on Nexus 4 using Android BLE API. I have a few questions/doubts:

1) Is there a way to set/override the connection or notification interval of BLE central device. I have found that for Android, the default connection interval is fixed to 7.5ms. Is there a way to change this connection/notification delay interval settings.

Source : http://processors.wiki.ti.com/index.php/Bluetooth_SensorTag?DCMP=lprf-stdroid&HQS=lprf-stdroid-pr-wiki1#Supported_Android_devices

2) On connecting to the remote device, I am facing an issue of getting disconnection after random period of time interval. There are many people facing the connection drop issue stating that android is unstable when they are using Android 4.3 API for BLE connection. Is there any solution for this?

EDIT

what else I observe here is when it is taking time to reconnect then it's coming with some L2CAP log ...following the log

Trying to create a new connection laststate_ BOND_NONE
D/BluetoothGatt( 9620): connect() - device: 1C:BA:81:11:CA:36, auto: true
D/BluetoothGatt( 9620): registerApp()
D/BluetoothGatt( 9620): registerApp() - UUID=1a9a0911-4d5c-41dc-8ac0-0284ef550510
D/BtGatt.GattService( 3208): registerClient() - UUID=1adsds0911-4sdsc-41dc-8ac0-0sdsdf550510
D/BtGatt.btif( 3208): btif_gattc_register_app
D/BtGatt.btif( 3208): btgattc_handle_event: Event 1000
D/BtGatt.btif( 3208): btif_gattc_upstreams_evt: Event 0
D/BtGatt.GattService( 3208): onClientRegistered() - UUID=1a9a0911-4d5c-41dc-8ac0-0284ef550510, clientIf=5
D/BluetoothGatt( 9620): onClientRegistered() - status=0 clientIf=5
D/BtGatt.GattService( 3208): clientConnect() - address=1C:BA:8C:1E:CA:36, isDirect=true
D/BtGatt.btif( 3208): btif_gattc_open
D/BtGatt.btif( 3208): btgattc_handle_event: Event 1004
D/BtGatt.btif( 3208): btif_get_device_type: Device [1c:ba:8c:1e:ca:36] type 2, addr. type 0
W/bt-l2cap( 3208): L2CAP - LE - cannot start new connection at conn st: 3

Any idea how can clear cahce mantain by L2CAP?

Answer 1

For your first question, as OneWorld said, it is advisable to let smartphone handle the connection delay interval settings. This settings are closely dependent on bluetooth hardware & stack used for particular smartphone.

About the disconnection issue, I also faced similar issues. I think, this is due to an issue logged in given link. When OS handles connection & pairing, you can not unpair the device and all the re-connection attempts fail after this. This doesn't happen if the device paired(& unpaired) programmatically using private APIs on 4.3, assuming you have have handled GATT connections correctly. In android 4.4.2, there is createBond API added for pairing. So with 4.4.2, communication works pretty well.

Regarding the stability of Bluetooth low energy on android, I can confirm that it is pretty unstable. I have tested an application installed on Nexus 4 & Nexus 5 with a low energy sensor. In spite of having the same OS version 4.4.2, both devices gave different results for connection. I observed that device got disconnected after certain time on Nexus 4 while for Nexus 5 things worked well.

Hope this helps you moving forward for your problem.

Answer 2

@Ashwini : As mentioned in the last comment with connection interval 7.5 it is working better for some amount of time. After some time, the L2CAP issue appears and the connectivity doesnt work unless the bluetooth adapter is reset. Also, a weird behavior is been noticed when the bluetooth adapter is disabled and re-enabled again programtically. We get the following GKI error below:

> /GKI_LINUX( 2232): ##### ERROR : GKI_exception: GKI_exception(): Task State Table
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: TASK ID [0] task name [BTU] state [0]
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: TASK ID [1] task name [BTIF] state [1]
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: TASK ID [2] task name [A2DP-MEDIA] state [1]
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: GKI_exception 65531 Sending to unknown dest#####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: 
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): 
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: * GKI_exception(): 65531 Sending to unknown dest
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): ##### ERROR : GKI_exception: ***************
> 02-05 15:49:24.466 E/GKI_LINUX( 2232): #####

Also, does this createBond API helps in improving the connection with BLE device (which actually doesnt need pairing for connection) ?

Answer 3

When I studied the Android BLE API, I could not find an API for changing the connection interval and supervision timeout (maybe slave latency as well, can't remember from the top of my head). I you do need to change these, you must do it from the slave device.

The answer from Ashwini you can just ignore, what he says is simply not correct. A Bluetooth 4.0 compliant master device must support connection intervals from 7.5 ms up to 4.0s. The slave device may request a change in connection parameters and sends a connection parameter update request, and the master will update the connection parameter accordingly.

On the other hand, the master (in your case the Android device) could have an interest in changing the connection interval on its own, in order to save power, and you would like to change the connection interval to a more relaxed interval.

In my opinion the Android API and even the hardware implementation on several devices are immature and using BLE, in the sense that BLE was intended, draws to much power on an Android device. In the future I believe you will see much better support on the API level and a division of the host and controller so that the controller can maintain connectivity even when the main CPU of the mobile device is sleeping. That will save a lot of power and you can maintain connectivity with your BLE devices 24/7 without any major constrain on you battery life.

Answer 4

I met auto disconnection problem same as your second question. Two ways to solve it:

1) Manually pair you Android device with the remote device through Bluetooth setting before running your application.

2) Or you can programmatically pair them in your code. Here's the pairing code I found online, which works for me

private void pairDevice(BluetoothDevice device) {
        try {
            Log.d("pairDevice()", "Start Pairing...");
            Method m = device.getClass()
                    .getMethod("createBond", (Class[]) null);
            m.invoke(device, (Object[]) null);
            Log.d("pairDevice()", "Pairing finished.");
        } catch (Exception e) {
            Log.e("pairDevice()", e.getMessage());
        }
    }

Answer 5

As for changing connection interval:

Since Android Lollipop API level 21 you can use: requestConnectionPriority() With 3 levels: CONNECTION_PRIORITY_BALANCED, CONNECTION_PRIORITY_HIGH or CONNECTION_PRIORITY_LOW_POWER.

It is still not so versatile as we developers would want, but at least something...