STM32F4 USART-Interrupt landet in def_irq_handler

int main(void)

{

    //PD5 (TXD) konfigurieren

    GPIO_InitTypeDef GPIO_initStructur;

    RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOD, ENABLE);

    GPIO_initStructur.GPIO_Pin = (1<<5);

    GPIO_initStructur.GPIO_Mode = GPIO_Mode_AF;

    GPIO_initStructur.GPIO_PuPd = GPIO_PuPd_NOPULL;

    GPIO_initStructur.GPIO_OType = GPIO_OType_PP;

    GPIO_initStructur.GPIO_Speed = GPIO_Speed_100MHz;

    GPIO_Init(GPIOD, &GPIO_initStructur);

    GPIO_PinAFConfig(GPIOD, 5, GPIO_AF_USART2); //USART2 auflegen

    //NVIC Konfigurieren

    NVIC_InitTypeDef NVIC_InitStructure;

    NVIC_InitStructure.NVIC_IRQChannel =  USART2_IRQn;

    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;

    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 0x0F;

    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0x0F;

    NVIC_Init(&NVIC_InitStructure);

    //USART2 konfigurieren

    RCC_APB1PeriphClockCmd(RCC_APB1ENR_USART2EN, ENABLE);

    USART_InitTypeDef Debug_init_s;

    Debug_init_s.USART_BaudRate = 256000;

    Debug_init_s.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

    Debug_init_s.USART_Mode = USART_Mode_Tx;

    Debug_init_s.USART_Parity = USART_Parity_No;

    Debug_init_s.USART_StopBits = USART_StopBits_1;

    Debug_init_s.USART_WordLength = USART_WordLength_8b;

    USART_DeInit(USART2);

    USART_Init(USART2, &Debug_init_s);

    //Flag auf 0 setzten damit der INterrupt nicht sofort kommt

    USART_ClearITPendingBit(USART2, USART_FLAG_TC); 

    USART_Cmd(USART2, ENABLE);

    //Interrupt aktivieren

    USART_ITConfig(USART2, USART_IT_TC, ENABLE);

    //Daten senden

    USART_SendData(USART2, 0x00);

    while(1)

    {

    }

}

void HardFault_Handler()

{

    while(1)

    {

    }

}

void USART2_IRQHandler()

{

    USART_ClearITPendingBit(USART2,USART_IT_TC);

    asm("nop");

    asm("nop");

    asm("nop");

    asm("nop");

    return;

}