Accurate timing in iOS

Question

I am looking at the \'Metronome\' sample code from the iOS SDK (http://developer.apple.com/library/ios/#samplecode/Metronome/Introduction/Intro.html). I am running the metro

Answer 1

If you need <100msec precision, look into CADisplayLink. It calls a selector at regular intervals, as fast as 60 times a second, i.e. every .0166667 sec.

If you want to do your metronome test, you'd set frameInterval to 60 so it gets called back once a second.

self.syncTimer = [CADisplayLink displayLinkWithTarget:self selector:@selector(syncFired:)];
self.syncTimer.frameInterval = 60;
[self.syncTimer addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSDefaultRunLoopMode];

-(void)syncFired:(CADisplayLink *)displayLink
{
    static NSTimeInterval lastSync = 0;
    NSTimeInterval now = CACurrentMediaTime();
    if (lastSync > 0) {
        NSLog(@"interval: %f", now - lastSync);
    }
    lastSync = now;
}

In my tests, that timer is called consistently every second within 0.0001 sec.

On the off chance you're running on a device with a different refresh rate than 60Hz, you'd have to divide displayLink.duration into 1.0 and round to the nearest integer (not the floor).