//代码
#include "stm32f10x.h"
#include "usart.h"
#include <stdio.h>

int main(void)
{
        Usart_Init(115200);
        while (1)
        {       
                printf(" I am in while loop ");
        }
}



//usart.c
#include "usart.h"
#include "stm32f10x.h"
#include <stdio.h>


int fputc(int ch, FILE *f)
{      
        while((USART1->SR&0X40)==0);//循环发送,直到发送完毕   
    USART1->DR = (u8) ch;      
        return ch;
}

void Usart_Init(unsigned int bound)
{       
        GPIO_InitTypeDef GPIO_InitStructure;
        USART_InitTypeDef USART_InitStructure;
        NVIC_InitTypeDef NVIC_InitStructure;
       
        RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA, ENABLE);

        GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
        GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
        GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
       
                GPIO_Init(GPIOA, &GPIO_InitStructure);
        //rxd PA10 浮空输入
        GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
        GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
       
                GPIO_Init(GPIOA, &GPIO_InitStructure);
       
       
        NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
        NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
        NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority  = 3;
        NVIC_InitStructure.NVIC_IRQChannelSubPriority = 3;
               
                NVIC_Init(&NVIC_InitStructure);
       
       
       
        USART_InitStructure.USART_BaudRate = bound;
  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_Init(USART1, &USART_InitStructure);
                USART_ITConfig(USART1,USART_IT_RXNE, ENABLE);
                USART_Cmd(USART1, ENABLE);
               
  printf(" USART is now ok! ");
}


//usart.h
#ifndef __USART_H
#define __USART_H

#include "stm32f10x.h"
void Usart_Init(unsigned int bound);

#endif


不知道为什么波特率会减半 比如我这里设置的115200波特率 下载到板子上打开串口调试工具 要调到57600波特率才能正常接收信息