实验代码 要求：使用STM32的串口来发送和接收数据。STM32通过串口和上位机的对话，STM32在收到上位机发过来的字符串后，原原本本的返回给上位机。

下面是一个简单的实验代码，可以实现STM32与上位机的串口通信，收到上位机发来的字符串后，原样返回给上位机：

#include "stm32f10x.h"
#include <stdio.h>

void USART1_Init(void);
void USART1_SendChar(char ch);
void USART1_SendString(char* str);
char USART1_ReceiveChar(void);
void USART1_ReceiveString(char* buffer, int buffer_size);

int main(void)
{
    USART1_Init(); // 初始化串口

    char buffer[128];
    while (1)
    {
        USART1_ReceiveString(buffer, sizeof(buffer)); // 接收上位机发来的字符串
        USART1_SendString(buffer); // 原样返回给上位机
    }
}

void USART1_Init(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;
    USART_InitTypeDef USART_InitStructure;
    NVIC_InitTypeDef NVIC_InitStructure;

    // 打开USART1和GPIOA的时钟
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1 | RCC_APB2Periph_GPIOA, ENABLE);

    // 配置USART1的TX引脚为复用推挽输出
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // 配置USART1的RX引脚为浮空输入
    GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_IN_FLOATING;
    GPIO_Init(GPIOA, &GPIO_InitStructure);

    // 配置USART1
    USART_InitStructure.USART_BaudRate = 115200;
    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);

    // 配置USART1中断
    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
    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);

    // 启动USART1
    USART_Cmd(USART1, ENABLE);
}

void USART1_SendChar(char ch)
{
    while (USART_GetFlagStatus(USART1, USART_FLAG_TXE) == RESET); // 等待发送缓冲区为空
    USART_SendData(USART1, ch); // 发送一个字符
}

void USART1_SendString(char* str)
{
    while (*str)
    {
        USART1_SendChar(*str++);
    }
}

char USART1_ReceiveChar(void)
{
    while (USART_GetFlagStatus(USART1, USART_FLAG_RXNE) == RESET); // 等待接收缓冲区非空
    return USART_ReceiveData(USART1); // 返回接收到的字符
}

void USART1_ReceiveString(char* buffer, int buffer_size)
{
    int i = 0;
    char ch;
    while (1)
    {
        ch = USART1_ReceiveChar();
        if (ch == '\r' || ch == '\n' || i == buffer_size - 1) // 收到回车、换行符或缓冲区满了，就停止接收
        {
            buffer[i] = '\0';
            break;
        }
        buffer[i++] = ch;
    }
}

void USART1_IRQHandler(void)
{
    if (USART_GetITStatus(USART1, USART_IT_RXNE) != RESET) // 接收到一个字符
    {
        USART_ClearITPendingBit(USART1, USART_IT_RXNE);
    }
}

在上位机的串口调试助手中，可以发送任意字符串给STM32，STM32将收到的字符串原样返回给上位机。