CMMotionManager: Device Calibration does not work on a real device - ios

Question

I've a strange behavior with CMMotionManager. I try to calibrate the position of my device to enable my App to support multiple device orientations.
When I debug my App on a real device (not in Simulator), everything is working fine.
When I run the same App without debugging, the calibration does not work.
Here's my code:
static CMMotionManager* _motionManager;
static CMAttitude* _referenceAttitude;
// Returns a vector with the current orientation values
// At the first call a reference orientation is saved to ensure the motion detection works for multiple device positions
+(GLKVector3)getMotionVectorWithLowPass{
// Motion
CMAttitude *attitude = self.getMotionManager.deviceMotion.attitude;
if (_referenceAttitude==nil) {
// Cache Start Orientation
_referenceAttitude = [_motionManager.deviceMotion.attitude copy];
} else {
// Use start orientation to calibrate
[attitude multiplyByInverseOfAttitude:_referenceAttitude];
NSLog(#"roll: %f", attitude.roll);
}
return [self lowPassWithVector: GLKVector3Make(attitude.pitch,attitude.roll,attitude.yaw)];
}
+(CMMotionManager*)getMotionManager {
if (_motionManager==nil) {
_motionManager=[[CMMotionManager alloc]init];
_motionManager.deviceMotionUpdateInterval=0.25;
[_motionManager startDeviceMotionUpdates];
}
return _motionManager;
}

Answer 1

I've found a solution. The issue was caused due the different timing behavior between debug and non debug mode. CMMotionManager needs a little time for initializing, before it returns correct values. The solution was to postpone the calibration for 0.25 seconds.
This code works:
+(GLKVector3)getMotionVectorWithLowPass{
// Motion
CMAttitude *attitude = self.getMotionManager.deviceMotion.attitude;
if (_referenceAttitude==nil) {
// Cache Start Orientation
// NEW:
[self performSelector:#selector(calibrate) withObject:nil afterDelay:0.25];
} else {
// Use start orientation to calibrate
[attitude multiplyByInverseOfAttitude:_referenceAttitude];
NSLog(#"roll: %f", attitude.roll);
}
return [self lowPassWithVector: GLKVector3Make(attitude.pitch,attitude.roll,attitude.yaw)];
}
// NEW:
+(void)calibrate
_referenceAttitude = [self.getMotionManager.deviceMotion.attitude copy]
}