On Jul 25, 2013, at 18:52 , [email protected] wrote:
> I'm getting about a half second lag behind the system clock.
> This is actually reasonable for my purposes, but I wonder if I'm missing
> something that might be more in sync.
You can do this using NSTimers, but you need to make sure you adjust for the
current fraction of a second. That is, if you simply set up a scheduled timer
with a one-second interval, you'll get called every second, but it won't
necessarily be at the instant the wall clock second ticks over.
So, thing to do is to create a repeating timer with a fire date rounded to the
next second and a one-second interval. Something like this (written
off-the-cuff, so might need some tweaking):
CFAbsoluteTime fireDateAbs = CFAbsoluteTimeGetCurrent();
fireDateAbs = trunc(fireDateAbs + 0.5); // Round
to the next second
NSDate* fireDate = [NSDate dateWithTimeIntervalSinceReferenceDate:
fireDateAbs];
mTimer = [[NSTimer alloc] initWithFireDate: fireDate interval: 1.0 target:
self selector: @selector(update:) userInfo: nil repeats: true];
[[NSRunLoop currentRunLoop] addTimer: mTimer forMode: NSRunLoopCommonModes];
--
Rick
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