sound and Nstimer stopped when iphone is in deepsl

I am creating an application in which I'm using nstimer and avaudioplayer to play sound,but both sound and timer stops when phone is in deep sleep mode.how to solve this issue?

here is the code to play audio

-(void)PlayTickTickSound:(NSString*)SoundFileName
{
//Get the filename of the sound file:
NSString *path = [NSString stringWithFormat:@"%@%@",[[NSBundle mainBundle] resourcePath],[NSString stringWithFormat:@"/%@",SoundFileName]];// @"/Tick.mp3"];
//Get a URL for the sound file
NSURL *filePath = [NSURL fileURLWithPath:path isDirectory:NO];
NSError *error;
if(self.TickPlayer==nil)
{
    self.TickPlayer = [[AVAudioPlayer alloc] initWithContentsOfURL:filePath error:&error];
    // handle errors here.
    self.TickPlayer.delegate=self;
    [self.TickPlayer setNumberOfLoops:-1];  // repeat forever
    [self.TickPlayer play];
}
else
{
    [self.TickPlayer play];
}
}

In order to prevent an app from going to sleep when the screen is locked, you must set your audio session to be of type kAudioSessionCategory_MediaPlayback.

Here's an example:

UInt32 category = kAudioSessionCategory_MediaPlayback;
OSStatus result = AudioSessionSetProperty(kAudioSessionProperty_AudioCategory,
                                        sizeof(category), &category);

if (result){
    DebugLog(@"ERROR SETTING AUDIO CATEGORY!\n");
}

result = AudioSessionSetActive(true);
if (result) {
    DebugLog(@"ERROR SETTING AUDIO SESSION ACTIVE!\n");
}

If you don't set the audio session category, then your app will sleep.

This will only continue to prevent the app from being put to sleep as long as you continue to play audio. If you stop playing audio and the screen is still locked, the app will go to sleep and your timers will be paused.

If you want the app to remain awake indefinitely, you'll need to play a "silent" audio file to keep it awake.

I have a code example of this here: Preventing iPhone Sleep