请教关于stm32f4的printf打印输出只输出点不输出数据的问题

hswkcg

在用f4调串口程序，本来是计算一个程序的执行时间，结果就是单纯的一个简单的printf串口打印输出都有问题，target中的Use Micro LIB选项选了，mian.c文件中包含了stdio.h文件，printf重定向也有了，串口，gpio初始化也有了，但是printf单纯的打印输出一个字符，结果串口看到的就是一个点，对，就是这个  .     郁闷坏了，不知道是什么原因，向大家请教，大家有遇到过这个问题的还请指导一下。   
这是输出结果图：

这是程序：

#include "stm32f4xx.h"

#include <stdio.h>

void OpenCom(void)

{

USART_InitTypeDef USART_InitStructure;

NVIC_InitTypeDef NVIC_InitStructure;

GPIO_InitTypeDef GPIO_InitStructure;

RCC_AHB1PeriphClockCmd(RCC_AHB1Periph_GPIOA, ENABLE);        

RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1);        

GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1);

GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9|GPIO_Pin_10;

GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;

GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;

GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;

GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;

GPIO_Init(GPIOA, &GPIO_InitStructure);

USART_InitStructure.USART_BaudRate = BaudRate;

USART_InitStructure.USART_WordLength = USART_WordLength_8b;

USART_InitStructure.USART_StopBits = USART_StopBits_1;

USART_InitStructure.USART_Parity = USART_Parity_No;

USART_InitStructure.USART_HardwareFlowControl = USART_HardwareFlowControl_None;

USART_InitStructure.USART_Mode = USART_Mode_Rx|USART_Mode_Tx;

USART_ITConfig(USART1,USART_IT_RXNE,ENABLE);

USART_Init(USART1, &USART_InitStructure);        /* USART configuration */

USART_Cmd(USART1, ENABLE); /* Enable USART */

USART_ClearFlag(USART1, USART_FLAG_TC);

NVIC_InitStructure.NVIC_IRQChannel=USART1_IRQn;

NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority=0;

NVIC_InitStructure.NVIC_IRQChannelSubPriority=0;

NVIC_InitStructure.NVIC_IRQChannelCmd=ENABLE;

NVIC_Init(&NVIC_InitStructure);

}

int main(void)

{

  unsigned char i='a';     

  OpenCom();

  printf("%c\r\n",i);      

}

int fputc(int ch,FILE *f)

{

USART_SendData(USART1,(unsigned char)ch);

while(!(USART1->SR&USART_FLAG_TXE));

return (ch);

}

hswkcg

BaudRate = 9600