#include"stm32f4xx.h"
void MY_USAR_Init()
{ 
GPIO_InitTypeDef GPIO_InitStruct;
USART_InitTypeDef USART_InitStruct;
NVIC_InitTypeDef  NVIC_InitStruct;

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA,ENABLE);
RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1,ENABLE);

GPIO_PinAFConfig(GPIOA,GPIO_Pin_9,GPIO_AF_USART1);
GPIO_PinAFConfig(GPIOA,GPIO_Pin_10,GPIO_AF_USART1);

GPIO_InitStruct.GPIO_Pin=GPIO_Pin_9|GPIO_Pin_10;
GPIO_InitStruct.GPIO_Mode=GPIO_Mode_AF;
GPIO_InitStruct.GPIO_OType=GPIO_OType_PP;
GPIO_InitStruct.GPIO_PuPd=GPIO_PuPd_UP;
GPIO_InitStruct.GPIO_Speed=GPIO_Speed_100MHz;
GPIO_Init(GPIOA,&GPIO_InitStruct);



USART_Cmd(USART1,ENABLE);
USART_InitStruct.USART_BaudRate=115200;
USART_InitStruct.USART_HardwareFlowControl=USART_HardwareFlowControl_None;
USART_InitStruct.USART_Mode=USART_Mode_Rx|USART_Mode_Tx;
USART_InitStruct.USART_Parity=USART_Parity_No;
USART_InitStruct.USART_StopBits=USART_StopBits_1;
USART_InitStruct.USART_WordLength=USART_WordLength_8b;
USART_Init(USART1,&USART_InitStruct);
USART_Cmd(USART1,ENABLE);

USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);
NVIC_InitStruct.NVIC_IRQChannel=USART1_IRQn;
NVIC_InitStruct.NVIC_IRQChannelCmd=ENABLE;
NVIC_InitStruct.NVIC_IRQChannelPreemptionPriority=1;
NVIC_InitStruct.NVIC_IRQChannelSubPriority=1;
NVIC_Init(&NVIC_InitStruct);


}

void USART1_IRQHandler(void)
{
u8 res;

if(USART_GetITStatus(USART1,USART_IT_RXNE)) 
{
res=USART_ReceiveData(USART1);
    USART_SendData(USART1,res);

  }

}

int main()
{
NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);
MY_USAR_Init();

while(1);


}
串口通信代码怎么不正常？？？？？？？？？？
求大侠帮忙