不准确的加速度计更新间隔

Question

我正在使用CoreMotion API，我想每10毫秒（100赫兹）保存加速度计的值。到目前为止我获得的更新间隔不准确。 这是我得到的更新间隔的示例（第二个）：

0.010414999997
0.0105919999769
0.0117060000193
0.0198359999922
0.00989700001082
0.0100809999858
0.0100519999978
0.0106810000143
0.010420000006
0.0107459999854
0.0105899999908
0.0105130000156
0.0104829999909
0.0107439999992
0.010391000018
0.0105859999894
0.0102320000005
0.010134000011
0.0101929999946
0.010666999995
0.00996399999713
0.0123709999898
0.0181950000115
0.0107940000016
0.00988500000676
0.0101469999936
0.0103529999906

如您所见，某些值高于10毫秒 更多信息：
- Xcode 3.2.6 / iOS4.3 / armv7
- 测试iPhone4 iOS5.1和iPodTouch4 iOS4.3.3
- 源代码：

-(void) viewDidLoad {
    started = NO;
    motionManager = [[CMMotionManager alloc] init];
    if ([motionManager isAccelerometerAvailable]) {
        motionManager.accelerometerUpdateInterval = 0.01; //100Hz
        motionQueue = [[NSOperationQueue alloc] init];
        [motionQueue setMaxConcurrentOperationCount:1]; // Serial operation queue
     } else {
         NSLog(@"Accelerometer is not available!\n");
     }
     NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
     NSMutableString *documentsDirectory = [[NSMutableString alloc] initWithString:[paths objectAtIndex:0]];
     path = [[NSMutableString alloc] init];
     [path setString:[NSString stringWithFormat:@"%@/timestamp.cap", documentsDirectory]];
    NSFileManager *fileManager = [NSFileManager defaultManager];
[fileManager removeItemAtPath:path error:NULL];
    [fileManager createFileAtPath:path contents:nil attributes:nil];
}


- (IBAction) startStopButton:(id) sender {
    if(!started) {
        started = YES;
        [sender setTitle:@"Stop" forState:UIControlStateNormal];
        CMAccelerometerHandler dataHandler = ^(CMAccelerometerData *accelerometerData, NSError *error) {
            NSString *content = [NSString stringWithFormat:@"%f\n", accelerometerData.timestamp];
            NSFileHandle *fh = [NSFileHandle fileHandleForWritingAtPath:path];
            [fh seekToEndOfFile];
            [fh writeData:[content dataUsingEncoding:NSUTF8StringEncoding]];
            [fh closeFile];
        };        
        [motionManager startAccelerometerUpdatesToQueue:motionQueue withHandler:dataHandler];
    } else {
        started = NO;
        [motionManager stopAccelerometerUpdates];
        [motionQueue waitUntilAllOperationsAreFinished];
        [sender setTitle:@"Start" forState:UIControlStateNormal];
    }
}

提前感谢您的回答。