使用C语言编写代码实现以下功能：循环接收串口数据自动缓冲处理解析出指令内容指令以#号开头以n结尾。

假设使用的是串口1，波特率为9600，以下是代码实现：

#include <stdio.h>
#include <string.h>
#include "stm32f4xx.h"

#define BUFFER_SIZE 128

char buffer[BUFFER_SIZE];
int buffer_index = 0;
int flag_receive = 0;

void USART1_IRQHandler(void)
{
  if (USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
  {
    char received = USART_ReceiveData(USART1);
    if (received == '#')
    {
      // 开始接收指令
      buffer_index = 0;
      flag_receive = 1;
    }
    else if (received == '\n')
    {
      // 指令接收完成
      flag_receive = 0;
      buffer[buffer_index] = '\0';
      printf("Received: %s\n", buffer);
    }
    else if (flag_receive && buffer_index < BUFFER_SIZE - 1)
    {
      // 正在接收指令
      buffer[buffer_index++] = received;
    }
  }
}

int main(void)
{
  // 初始化串口1
  USART_InitTypeDef USART_InitStructure;
  GPIO_InitTypeDef GPIO_InitStructure;
  NVIC_InitTypeDef NVIC_InitStructure;

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

  // 配置PA9为复用功能，用于USART1_TX
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_9;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
  GPIO_InitStructure.GPIO_OType = GPIO_OType_PP;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_UP;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  // 配置PA10为复用功能，用于USART1_RX
  GPIO_InitStructure.GPIO_Pin = GPIO_Pin_10;
  GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF;
  GPIO_InitStructure.GPIO_PuPd = GPIO_PuPd_NOPULL;
  GPIO_Init(GPIOA, &GPIO_InitStructure);

  GPIO_PinAFConfig(GPIOA, GPIO_PinSource9, GPIO_AF_USART1); // 将PA9引脚复用为USART1_TX
  GPIO_PinAFConfig(GPIOA, GPIO_PinSource10, GPIO_AF_USART1); // 将PA10引脚复用为USART1_RX

  USART_InitStructure.USART_BaudRate = 9600;
  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);

  // 使能USART1接收中断
  USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);

  // 配置USART1中断优先级
  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);

  USART_Cmd(USART1, ENABLE);

  while (1)
  {
    // 程序主循环
  }
}

解释一下代码：

1. 定义了一个长度为128的缓冲区buffer，一个缓冲区指针buffer_index，以及一个标志位flag_receive，表示当前是否在接收指令。
2. 在USART1_IRQHandler中断处理函数中，判断接收到的字符是否为#，如果是，则说明开始接收指令，将缓冲区指针归零，标志位设为1；如果接收到的字符为\n，则说明指令接收完成，标志位设为0，缓冲区最后一个字符设为\0，即字符串结尾标志，然后打印出接收到的指令。
3. 在主函数中，初始化USART1，使能接收中断，配置中断优先级，然后进入主循环