[IPhone SDK] NSTimer conflicts with touch events

Question

Hi all,
i've an NSTimer that refresh the UIView at 30 fps. Below there is the scheduled timer:
animationTimer = [NSTimer scheduledTimerWithTimeInterval:animationInterval target:self selector:@selector(refreshAll) userInfo:nil repeats:YES];
The problem is that the app doesn't wrap the touch events (touchbegan, touchesMoved and touchEnded) because the timer interval is too low and conflicts with this events.
I tried to set the animation interval to 2 seconds and the touch events works but the rendering obviously is slow.
However the problem is only on the device because when i launch the app on the simulator i have no problem with the timer.
Can anyone tell me how I can solve this problem?
Thanks

Answer 1

The game I'm developing for the iPhone has 2 play modes (the second mode has more on screen objects). In the first game mode, I get a solid 29-30 frames per second (acceptable), however the second mode with more objects gives me 25 fps (slightly jerky). BTW, on a PC with modern hardware I get >1300 fps @1680x1050.
At first I thought that the NSTimer resolution might be causing problems. The Apple demos all use a resolution of 1/60. Setting a value of 0.0 actually bumps the frame rate up by few frames, but I lose the ability to process touch input (crap). Adding usleep(a_delta) hoping to invode a context switch does nothing for the touch input.
The next thing I tried was creating a dedicated rendering thread which basically does a while (1) render(); The thread will loop as fast as it can, and I regain touch input. On the plus side, I gained 3-4 fps for both game modes, so now I can hit 30 fps for the second mode (sweet).
To make this work, I obviously needed to add locking primitives between the render thread and the iphone input (touch, sleep, phone call etc). The render loop is now basically:
while (alive)
aLock->Lock();
render();
aLock->Unlock();
Anyway, I thought people would appretiate my experience when looking to squeeze a few more frames out of the iPhone. You just need to understand multiprocessing to work out the synchronisation issues.
PS. There is some interesting advice in the following thread:
http://discussions.apple.com/thread.jspa?messageID=7898898&#7898898
Basically, they set invoke the runloop from the animation method. This might be simpler than spawning threads and handling locking, but I haven't tried it.