请帮我设计一个stm32f103程序使其可以接收来自python串口通信的字符，并根据接受的字符控制两个级联MAX7219led点阵在未接收到字符时都显示问号，接收1，2，3，4，时分别显示上下左右的四个箭头的表情

好的，下面是一个简单的实现代码，你可以参考一下：

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

#define USART_RX_BUF_SIZE 64
#define MAX7219_CS_Pin GPIO_Pin_4
#define MAX7219_CS_GPIO GPIOA
#define MAX7219_DIN_Pin GPIO_Pin_5
#define MAX7219_DIN_GPIO GPIOA
#define MAX7219_CLK_Pin GPIO_Pin_7
#define MAX7219_CLK_GPIO GPIOA

uint8_t usart_rx_buf[USART_RX_BUF_SIZE];
uint8_t usart_rx_len = 0;
uint8_t arrow_up[8] = {0x08, 0x1C, 0x36, 0x63, 0x41, 0x41, 0x41, 0x00};
uint8_t arrow_down[8] = {0x00, 0x41, 0x41, 0x41, 0x63, 0x36, 0x1C, 0x08};
uint8_t arrow_left[8] = {0x08, 0x0C, 0x0E, 0xFF, 0xFF, 0x0E, 0x0C, 0x08};
uint8_t arrow_right[8] = {0x10, 0x18, 0x1C, 0xFF, 0xFF, 0x1C, 0x18, 0x10};

void GPIO_Configuration(void)
{
    GPIO_InitTypeDef GPIO_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);

    GPIO_InitStructure.GPIO_Pin = MAX7219_CS_Pin | MAX7219_DIN_Pin | MAX7219_CLK_Pin;
    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_Init(GPIOA, &GPIO_InitStructure);
}

void USART_Configuration(void)
{
    USART_InitTypeDef USART_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_USART1, ENABLE);

    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_Init(USART1, &USART_InitStructure);
    USART_Cmd(USART1, ENABLE);

    USART_ITConfig(USART1, USART_IT_RXNE, ENABLE);
}

void NVIC_Configuration(void)
{
    NVIC_InitTypeDef NVIC_InitStructure;

    NVIC_PriorityGroupConfig(NVIC_PriorityGroup_2);

    NVIC_InitStructure.NVIC_IRQChannel = USART1_IRQn;
    NVIC_InitStructure.NVIC_IRQChannelPreemptionPriority = 1;
    NVIC_InitStructure.NVIC_IRQChannelSubPriority = 0;
    NVIC_InitStructure.NVIC_IRQChannelCmd = ENABLE;
    NVIC_Init(&NVIC_InitStructure);
}

void MAX7219_SendByte(uint8_t byte)
{
    uint8_t i;
    GPIO_ResetBits(MAX7219_CS_GPIO, MAX7219_CS_Pin);
    for(i = 8; i > 0; i--)
    {
        GPIO_ResetBits(MAX7219_CLK_GPIO, MAX7219_CLK_Pin);
        if(byte & 0x80)
            GPIO_SetBits(MAX7219_DIN_GPIO, MAX7219_DIN_Pin);
        else
            GPIO_ResetBits(MAX7219_DIN_GPIO, MAX7219_DIN_Pin);
        byte <<= 1;
        GPIO_SetBits(MAX7219_CLK_GPIO, MAX7219_CLK_Pin);
    }
    GPIO_SetBits(MAX7219_CS_GPIO, MAX7219_CS_Pin);
}

void MAX7219_SendCmd(uint8_t cmd, uint8_t data)
{
    uint8_t i;
    GPIO_ResetBits(MAX7219_CS_GPIO, MAX7219_CS_Pin);
    for(i = 8; i > 0; i--)
    {
        GPIO_ResetBits(MAX7219_CLK_GPIO, MAX7219_CLK_Pin);
        if(i == 8)
            MAX7219_SendByte(cmd);
        else
            MAX7219_SendByte(data);
        GPIO_SetBits(MAX7219_CLK_GPIO, MAX7219_CLK_Pin);
    }
    GPIO_SetBits(MAX7219_CS_GPIO, MAX7219_CS_Pin);
}

void MAX7219_Init(void)
{
    MAX7219_SendCmd(0x09, 0x00);
    MAX7219_SendCmd(0x0A, 0x03);
    MAX7219_SendCmd(0x0B, 0x07);
    MAX7219_SendCmd(0x0C, 0x01);
    MAX7219_SendCmd(0x0F, 0x00);
    MAX7219_SendCmd(0x0E, 0x00);
}

void MAX7219_Display(uint8_t *data)
{
    uint8_t i, j;
    for(i = 1; i <= 8; i++)
    {
        MAX7219_SendCmd(i, data[i-1]);
    }
}

void USART1_IRQHandler(void)
{
    if(USART_GetITStatus(USART1, USART_IT_RXNE) != RESET)
    {
        usart_rx_buf[usart_rx_len++] = USART_ReceiveData(USART1);
        if(usart_rx_len >= USART_RX_BUF_SIZE)
            usart_rx_len = 0;
        USART_ClearITPendingBit(USART1, USART_IT_RXNE);
    }
}

int main(void)
{
    GPIO_Configuration();
    USART_Configuration();
    NVIC_Configuration();
    MAX7219_Init();

    while(1)
    {
        if(usart_rx_len > 0)
        {
            switch(usart_rx_buf[usart_rx_len-1])
            {
                case '1':
                    MAX7219_Display(arrow_up);
                    break;
                case '2':
                    MAX7219_Display(arrow_down);
                    break;
                case '3':
                    MAX7219_Display(arrow_left);
                    break;
                case '4':
                    MAX7219_Display(arrow_right);
                    break;
                default:
                    MAX7219_Display((uint8_t*)"????????");
                    break;
            }
            usart_rx_len = 0;
        }
        else
        {
            MAX7219_Display((uint8_t*)"????????");
        }
    }
}

这个程序通过USART1接收来自Python串口通信的字符，根据接收到的字符控制MAX7219点阵的显示。在未接收到字符时，程序会一直显示问号。MAX7219点阵的显示数据通过一个8字节的数组来表示，分别对应MAX7219点阵的8行数据。在本程序中，我们定义了四个数组，分别表示上下左右四个箭头的表情。在接收到1，2，3，4时，程序会分别显示这四个数组中的数据。

需要注意的是，本程序中使用了中断方式接收USART数据，所以需要在配置NVIC时开启USART1中断，并在USART1_IRQHandler中处理接收到的数据。