CoreMotion Accelerometer iPhone 5与iPod（5代）

Question

我正在运行iOS 7.0.4的iPhone 5和iPod（第5代）上执行以下代码。在iPhone上，更新几乎是实时的，而在iPod上有一个显着的延迟。我做错了什么导致这种差异？它们不应该是一样的吗？

motionManager = [[CMMotionManager alloc] init];
motionManager.accelerometerUpdateInterval  = 1.0/20.0; // Update at 20Hz
if (motionManager.accelerometerAvailable) {
    NSLog(@"Accelerometer avaliable");
    queue = [NSOperationQueue currentQueue];
    [motionManager startDeviceMotionUpdatesToQueue:queue
                                        withHandler:^(CMDeviceMotion *accelerometerData, NSError *error) {
                                            CMAcceleration useracceleration = accelerometerData.userAcceleration;
                                            xLabel.text = [NSString stringWithFormat:@"%f", useracceleration.x];
                                            xBar.progress = ABS(useracceleration.x);

                                            yLabel.text = [NSString stringWithFormat:@"%f", useracceleration.y];
                                            yBar.progress = ABS(useracceleration.y);

                                            zLabel.text = [NSString stringWithFormat:@"%f", useracceleration.z];
                                            zBar.progress = ABS(useracceleration.z);

                                            force = (bodymass * sqrt((pow(useracceleration.x,2) + pow(useracceleration.y,2) + pow(useracceleration.z,2))));



                                            forceLabel.text = [NSString stringWithFormat:@"%f", force];
                                            forceBar.progress = ABS(force);

                                        }];


}

请帮助...我希望此代码能够在两台设备上准确运行。谢谢！