Android accelerometer sensor listener frequency changing unexpectedly

Question

I have an application which calls sensorManager.registerListener() for the accelerometer, gyroscope, and magnetometer, which registers all sensors for the handler and they are each set to SENSOR_DELAY_NORMAL. This works fine with no issues the vast majority of the time.

However, when looking at some logs I noticed the accelerometer would seemingly randomly change is frequency from roughly 179ms (which seems the be the average SENSOR_DELAY_NORMAL on my phone) to about 20ms.

After doing a fair amount of digging and testing, I found the cause to be when the phone is shaken rapidly. When this happens all other sensors will maintain their ~179ms rate, but only the accelerometer will increase its rate to ~20ms. After some period of time the rate will eventually decrease from ~20ms back to the set rate of ~179ms.

I'm not sure how long it takes for it to return to the ~179ms rate, I've tried uninstalled and reinstalling the application and if enough time has not passed yet the accelerometer will still be firing events at ~20ms.

I wanted to see if I could resolve the issue but un-registering and re-registering the listener at the correct rate when this happens, however the accelerometer will keep going at ~20ms irregardless of what I reset it to. I did find out though that I can unregister the accelerometer listener, and that seems to work, but it doesn't solve my problem.

Anybody know why the accelerometer listener would change its rate at which it's firing, and how I might be able to resolve this?

Answer 1

The delay that you request Android for is only a suggested delay. Android system and other applications can change this. Source

The reason why this can happen is quite simple -

• There are only limited number of physical sensors available on the device, 1 accelerometer, 1 magnetometer, 1 gyroscope
• Say your application, registers for all events from accelerometer every 100ms.
• Another application, requests for all events from accelerometer every 10ms
• Now since there is only one sensor and there 2 different needs, Android enables the accelerometer to provide the data at the lowest of all delay requests made by all the apps and then Android reports all events at this delay frequency only.
• In this case, it is up to the application developer to disregard events when they are in excess to what is required.