Timer Interrupt am STM32F103RB

Hallo,

ich versuche mit dem  STM32F103 ein Timer Interrupt hin zu bekommen.
Allegings wird das Interrupt nie ausgeführt und der Controller bleib 
irgendwo im Programm hängen.

Kann mir da jemand einen Tip geben?



#include <stm32f10x_gpio.h>
#include <stm32f10x_rcc.h>
#include <stm32f10x_tim.h>
#include <stm32f10x.h>
#include <misc.h>

 timer_init()
{
  TIM_TimeBaseInitTypeDef    TIM_TimeBaseStructure;
  NVIC_InitTypeDef NVIC_InitStructure;

  RCC_APB1PeriphClockCmd(RCC_APB1Periph_TIM2, ENABLE);


  TIM_TimeBaseStructInit(&TIM_TimeBaseStructure);
  TIM_TimeBaseStructure.TIM_ClockDivision = TIM_CKD_DIV1;
  TIM_TimeBaseStructure.TIM_Prescaler = 1000-1;
  //TIM_TimeBaseStructure.TIM_Period = 8400-1;

  TIM_TimeBaseStructure.TIM_CounterMode = TIM_CounterMode_Up;
  TIM_TimeBaseStructure.TIM_RepetitionCounter = 0;
  TIM_TimeBaseInit(TIM2, &TIM_TimeBaseStructure);

  TIM_ITConfig(TIM2, TIM_IT_Update, ENABLE);


  NVIC_InitStructure.NVIC_IRQChannel = TIM2_IRQn;
  NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
  NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
  NVIC_InitStructure.NVIC_IRQChannelSubPriority = 1;
  NVIC_Init(&NVIC_InitStructure);


  TIM3->CR1 = TIM_CR1_CEN;
}

void TIM2_IRQHandler()
{
  while ((TIM2->SR & (1 << 0)) > 0) TIM2->SR &= ~(1 << 0);
  GPIOA->BSRR = (1 << 5);
}
int main()
{
  GPIO_InitTypeDef GPIO_InitStructure;

  RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_5;

  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  timer_init();


  while (1)
  {

  }}