static int period_to_usecs(struct snd_pcm_runtime *runtime)
{
	int usecs;

	if (! runtime->rate)
		return -1; /* invalid */

	/* take 75% of period time as the deadline */
	usecs = (750000 / runtime->rate) * runtime->period_size;
	usecs += ((750000 % runtime->rate) * runtime->period_size) /
		runtime->rate;

	return usecs;
}
static int period_to_usecs(struct snd_pcm_runtime *runtime)
{
	int usecs;

	if (! runtime->rate)
		return -1;  

	 
	usecs = (750000 / runtime->rate) * runtime->period_size;
	usecs += ((750000 % runtime->rate) * runtime->period_size) /
		runtime->rate;

	return usecs;
}