TImer problem samr21-xpro

Dear RIOT Team,

the function "timer_init" does not work. The function returns 0. So my function call is correct. But the ISR function is never called. Why ? I have read the doc but found nothing to solve the problem. Did i forget something ?

My Code:

Hi Oliver, please provide more information, e.g. the board you are using including Makefile for your app. Best Regards Robert