android - Accelerometer stops delivering samples when the screen is off on Droid/Nexus One even with a WakeLock

Question

I have some code that extends a service and records onSensorChanged(SensorEvent event) accelerometer sensor readings on Android. I would like to be able to record these sensor readings even when the device is off (I'm careful with battery life and it's made obvious when it's running). While the screen is on the logging works fine on a 2.0.1 Motorola Droid and a 2.1 Nexus One.

However, when the phone goes to sleep (by pushing the power button) the screen turns off and the onSensorChanged events stop being delivered (verified by using a Log.e message every N times onSensorChanged gets called).

The service acquires a wakeLock to ensure that it keeps running in the background; but, it doesn't seem to have any effect. I've tried all the various PowerManager. wake locks but none of them seem to matter.

_WakeLock = _PowerManager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, "My Tag");
_WakeLock.acquire();

There have been conflicting reports about whether or not you can actually get data from the sensors while the screen is off... anyone have any experience with this on a more modern version of Android (Eclair) and hardware?

This seems to indicate that it was working in Cupcake: http://groups.google.com/group/android-developers/msg/a616773b12c2d9e5

PS: The exact same code works as intended in 1.5 on a G1. The logging continues when the screen turns off, when the application is in the background, etc.

Answer 1

We've deduced this started as of 2.0.1. It seems to be intentional, perhaps part of the battery life boost that was touted as a feature. We had a working shake to wakeup or unlock on 2.0, then it broke on the update and we haven't been able to get any kind of workaround. ;'( It doesn't matter if CPU partial lock is held which is supposed to always prevent CPU from sleeping. From what I've seen logging debug over USB there appears to occasionally be mention of sensor listener changes as sleep happens.

A user posted a workaround that he claimed works on the motorola devices - https://sites.google.com/a/bug-br.org.br/android/technical-documents

I tested the workaround, coming up with the following code from the tutorial and some manual revision (there are a few "bugs" in his tutorial presented code):

public class ShakeWakeupService extends Service implements SensorEventListener{
     private Context mContext;
     SensorManager mSensorEventManager;
     Sensor mSensor;

     // BroadcastReceiver for handling ACTION_SCREEN_OFF.
     public BroadcastReceiver mReceiver = new BroadcastReceiver() {

         @Override
         public void onReceive(Context context, Intent intent) {
             // Check action just to be on the safe side.
             if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
                 Log.v("shake mediator screen off","trying re-registration");
                 // Unregisters the listener and registers it again.
                 mSensorEventManager.unregisterListener(ShakeWakeupService.this);
                 mSensorEventManager.registerListener(ShakeWakeupService.this, mSensor,
                     SensorManager.SENSOR_DELAY_NORMAL);
             }
         }
     };

         @Override
         public void onCreate() {
           super.onCreate();
           Log.v("shake service startup","registering for shake");
           mContext = getApplicationContext();
             // Obtain a reference to system-wide sensor event manager.
           mSensorEventManager = (SensorManager) mContext.getSystemService(Context.SENSOR_SERVICE);
             // Get the default sensor for accel
           mSensor = mSensorEventManager.getDefaultSensor(Sensor.TYPE_ACCELEROMETER);
             // Register for events.
           mSensorEventManager.registerListener(this, mSensor, SensorManager.SENSOR_DELAY_NORMAL);

             // Register our receiver for the ACTION_SCREEN_OFF action. This will make our receiver
             // code be called whenever the phone enters standby mode.
           IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_OFF);
           registerReceiver(mReceiver, filter);
     }

     @Override
     public void onDestroy() {
        // Unregister our receiver.
         unregisterReceiver(mReceiver);
         // Unregister from SensorManager.
         mSensorEventManager.unregisterListener(this);
     }

     @Override
     public IBinder onBind(Intent intent) {
         // We don't need a IBinder interface.
  return null;
     }

 public void onShake() {
         //Poke a user activity to cause wake?
     }
     public void onAccuracyChanged(Sensor sensor, int accuracy) {
                //not used right now
            }
            //Used to decide if it is a shake
            public void onSensorChanged(SensorEvent event) {
                    if(event.sensor.getType() != Sensor.TYPE_ACCELEROMETER) return;
                  Log.v("sensor","sensor change is verifying");
            }
      }

The workaround works for me, but will not work while I have screebl running, which is a feature a lot of my users really want working in conjunction with what I'm developing.