Archived:MIDlet cannot power down GPS module with an existing satellite fix (Known Issue)
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Overview
When using Location API's (JSR-179) methods to get a proper provider, it is not possible to stop GPS module location activity if there is a GPS satellite fix, resulting in reduced battery life.
Description
Location API's getInstance(Criteria criteria) method selects the location provider based on the defined criteria, where the value null indicates the least restrictive criteria with default values.
Example usage for acquiring location provider information with JSR-179:
..
LocationProvider locProvider;
..
locProvider = LocationProvider.getInstance(null);
locProvider.setLocationListener(this, -1, 0, 0); //setting listener for LocationProvider updates
When acquiring location provider information as defined above, the Location API does not stop GPS module location activity if there is a GPS satellite fix. When the location listener is stopped and the location provider is reset, the actual receiver does not stop and it does not power down (regardless of whether the satellite fix continues to be available or not):
locProvider.setLocationListener(null, -1, 0, 0); // setting registered listener cancelled
locProvider.reset(); // resetting LocationProvider by aborting all pending synchronous requests
As a result, battery life is reduced to below 10 hours.
How to reproduce
Download and install Nokia Energy Profiler.
Implement a test MIDlet using this source code.
Procedures:
- Launch Nokia Energy Profiler. From Options, choose Start to begin measurement and check the initial battery level in the top right corner.
- Leave Nokia Energy Profiler running and exit it by pressing the Menu key.
- Launch the test MIDlet. The MIDlet starts searching for a fix. After a fix has been found, press Stop GPS. Leave the MIDlet running and exit it by pressing the Menu key.
- Resume to the Nokia Energy Profiler and check the battery level. It is now reduced to below 10 hours.
- Repeat step 2.
- Resume to the running MIDlet and close it by pressing Exit.
- Repeat step 4. The battery level will be slowly resumed. Close the Profiler by pressing Exit. Relaunch the Profiler and start the measurement again to view the improved battery level.
Solution
Exiting the MIDlet results in improved battery level.
Update November 2011
A few considerations need to be made regarding the issue mentioned here. Ideally, when setting the location listener, the default values for interval, time out and max age, should be passed to the Location Listener object. For testing purposes it would make sense to replace this line:
provider.setLocationListener(this, -1, 0, 0);
with this one:
provider.setLocationListener(this, -1, -1, -1);
Another thing, that requires attention is the fact that when trying to stop the location listener from listening to location updates, the following code:
provider.setLocationListener(null, -1, 0, 0);
should be replaced with:
provider.setLocationListener(this, 0, 0, 0);
This is in order for the location listener to be replaced with a new object that does not listen for location updates. Only one location listener can be registered with the given location provider. Registering again a location listener to the given provider, means that the new one replaces the old one. Setting the interval of the listener to 0, indicates that the application wants to receive only provider status updates and not location updates. In this case, the values of time out and max Age, don’t matter. The LocationListener argument of the setLocationListener method needs to change from null to this in order for the method to refer to a valid LocationListener object, since the midlet implements the LocationListener interface.
After performing the above changes, I tested the behavior of the application on various platforms and devices, in order to see how the GPS usage affects the Power Consumptions. Bellow are my findings:
3rd Edition FP1- Nokia E71
5th Edition - Nokia C5-03
Symbian Anna - Nokia C06-01
Conclusion
From the above results, it is visible that the power consumption before and after stopping the GPS module from within the application, improves greatly in later Symbian platforms. In Symbian Anna for example, this is no longer an issue.
