title: no onCharacteristicChanged callbacks received from TI SensorTag
body: <p>I have a TI Sensor Tag that I'm trying to interface with Android using BLE. I'm following the instructions here: <a href="http://processors.wiki.ti.com/index.php/SensorTag_User_Guide#SensorTag_Android_Development" rel="nofollow">http://processors.wiki.ti.com/index.php/SensorTag_User_Guide#SensorTag_Android_Development</a> and things work up until the last step, I am not receiving onCharacteristicChanged callbacks.  Note: I do receive ONE onCharacteristicWrite callback, but nothing after that. Please help!</p>
  
  <p>At first I thought this might be due to the synchronous callbacks &amp; queue issue explained in the instructions, but I implemented that and it didn't solve the problem.</p>
  
  <p>Applicable classes of my code: <a href="https://github.com/bhadley/ble_testing/tree/master/src/com/example/helloworld" rel="nofollow">https://github.com/bhadley/ble_testing/tree/master/src/com/example/helloworld</a></p>
  
  <pre><code>D/BtGatt.GattService(  771): onGetDescriptor() - address=BC:6A:29:AC:72:D9, stat
  us=0, descUuid=00002901-0000-1000-8000-00805f9b34fb
  D/BluetoothGatt( 3500): onGetDescriptor() - Device=BC:6A:29:AC:72:D9 UUID=000029
  01-0000-1000-8000-00805f9b34fb
  D/BtGatt.btif(  771): btif_gattc_get_descriptor
  D/BtGatt.btif(  771): btgattc_handle_event: Event 1010
  D/BtGatt.GattService(  771): onGetDescriptor() - address=BC:6A:29:AC:72:D9, stat
  us=133, descUuid=00002901-0000-1000-8000-00805f9b34fb
  D/BluetoothGatt( 3500): onSearchComplete() = Device=BC:6A:29:AC:72:D9 Status=0
  I/BLE     ( 3500): onServicesDiscovered
  D/BluetoothGatt( 3500): writeCharacteristic() - uuid: f000aa32-0451-4000-b000-00
  0000000000
  D/BtGatt.GattService(  771): writeCharacteristic() - address=BC:6A:29:AC:72:D9
  D/BtGatt.btif(  771): btif_gattc_write_char
  D/BtGatt.btif(  771): btgattc_handle_event: Event 1015
  D/BluetoothGatt( 3500): setCharacteristicNotification() - uuid: f000aa31-0451-40
  00-b000-000000000000 enable: true
  D/BtGatt.GattService(  771): registerForNotification() - address=BC:6A:29:AC:72:
  D9 enable: true
  D/BtGatt.btif(  771): btif_gattc_reg_for_notification
  D/BtGatt.btif(  771): btgattc_handle_event: Event 1018
  D/BluetoothGatt( 3500): writeDescriptor() - uuid: 00002902-0000-1000-8000-00805f
  9b34fb
  D/BtGatt.GattService(  771): onRegisterForNotifications() - address=null, status
  =0, registered=1, charUuid=f000aa31-0451-4000-b000-000000000000
  D/BtGatt.GattService(  771): writeDescriptor() - address=BC:6A:29:AC:72:D9
  D/BtGatt.btif(  771): btif_gattc_write_char_descr
  D/BtGatt.btif(  771): btgattc_handle_event: Event 1016
  E/bt-btif (  771): already has a pending command!!
  I/BLE     ( 3500): status of enabling magnetometer notifications: true
  D/BtGatt.btif(  771): btif_gattc_upstreams_evt: Event 4
  D/BtGatt.GattService(  771): onWriteCharacteristic() - address=BC:6A:29:AC:72:D9
  , status=0
  D/BluetoothGatt( 3500): onCharacteristicWrite() - Device=BC:6A:29:AC:72:D9 UUID=
  f000aa32-0451-4000-b000-000000000000 Status=0
  I/BLE     ( 3500): onCharacteristicWrite
  </code></pre>