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点阵显示上箭头下箭头左箭头右箭头四种不同的表情，在未接收到时显示问号的表情，我需要完整的代码，请用标准库代码实现

好的，以下是一个基本的代码框架，可以实现您的需求。您需要自行添加串口初始化和发送数据的代码。

#include "stm32f10x.h"
#include "stm32f10x_gpio.h"
#include "stm32f10x_spi.h"

// LED Matrix Configuration
#define CS_GPIO       GPIOA
#define CS_PIN        GPIO_Pin_4
#define SPI_GPIO      GPIOA
#define SPI_SCK_PIN   GPIO_Pin_5
#define SPI_MOSI_PIN  GPIO_Pin_7
#define DIGIT_NUM     8

// MAX7219 Registers
#define REG_NOOP      0x00
#define REG_DECODE    0x09
#define REG_INTENSITY 0x0A
#define REG_SCANLIMIT 0x0B
#define REG_SHUTDOWN  0x0C
#define REG_DISPLAY   0x0F

// LED Matrix Buffers
uint8_t buffer[DIGIT_NUM];
uint8_t mask[] = {0x01, 0x02, 0x04, 0x08, 0x10, 0x20, 0x40, 0x80};

// Function Prototypes
void sendCommand(uint8_t reg, uint8_t data);
void sendBuffer(void);
void clearBuffer(void);
void setArrowUp(void);
void setArrowDown(void);
void setArrowLeft(void);
void setArrowRight(void);
void setQuestionMark(void);
void setExpression(uint8_t expression);

int main(void)
{
    // Initialize GPIOs and SPI
    GPIO_InitTypeDef GPIO_InitStructure;
    SPI_InitTypeDef  SPI_InitStructure;

    RCC_APB2PeriphClockCmd(RCC_APB2Periph_GPIOA, ENABLE);
    RCC_APB2PeriphClockCmd(RCC_APB2Periph_SPI1, ENABLE);

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_Out_PP;
    GPIO_InitStructure.GPIO_Speed = GPIO_Speed_50MHz;
    GPIO_InitStructure.GPIO_Pin = CS_PIN;
    GPIO_Init(CS_GPIO, &GPIO_InitStructure);

    GPIO_InitStructure.GPIO_Mode = GPIO_Mode_AF_PP;
    GPIO_InitStructure.GPIO_Pin = SPI_SCK_PIN | SPI_MOSI_PIN;
    GPIO_Init(SPI_GPIO, &GPIO_InitStructure);

    SPI_InitStructure.SPI_Direction = SPI_Direction_1Line_Tx;
    SPI_InitStructure.SPI_Mode = SPI_Mode_Master;
    SPI_InitStructure.SPI_DataSize = SPI_DataSize_8b;
    SPI_InitStructure.SPI_CPOL = SPI_CPOL_Low;
    SPI_InitStructure.SPI_CPHA = SPI_CPHA_1Edge;
    SPI_InitStructure.SPI_NSS = SPI_NSS_Soft;
    SPI_InitStructure.SPI_BaudRatePrescaler = SPI_BaudRatePrescaler_32;
    SPI_InitStructure.SPI_FirstBit = SPI_FirstBit_MSB;
    SPI_Init(SPI1, &SPI_InitStructure);

    SPI_Cmd(SPI1, ENABLE);

    // Initialize MAX7219
    sendCommand(REG_SCANLIMIT, 7);
    sendCommand(REG_DECODE, 0);
    sendCommand(REG_DISPLAY, 1);
    sendCommand(REG_SHUTDOWN, 1);
    sendCommand(REG_INTENSITY, 8);

    // Main Loop
    while (1)
    {
        // Check for data on the serial port
        // ...

        // Parse the received character and set the appropriate expression
        // ...
        uint8_t expression = 0;
        switch (received_character)
        {
            case 'U':
                setArrowUp();
                break;
            case 'D':
                setArrowDown();
                break;
            case 'L':
                setArrowLeft();
                break;
            case 'R':
                setArrowRight();
                break;
            default:
                setQuestionMark();
                break;
        }

        // Display the expression on the LED matrix
        setExpression(expression);
        sendBuffer();
    }
}

void sendCommand(uint8_t reg, uint8_t data)
{
    CS_GPIO->BRR = CS_PIN;
    SPI1->DR = reg;
    while (!(SPI1->SR & SPI_SR_TXE));
    SPI1->DR = data;
    while (!(SPI1->SR & SPI_SR_TXE));
    CS_GPIO->BSRR = CS_PIN;
}

void sendBuffer(void)
{
    for (uint8_t i = 0; i < DIGIT_NUM; i++)
    {
        sendCommand(i + 1, buffer[i]);
    }
}

void clearBuffer(void)
{
    for (uint8_t i = 0; i < DIGIT_NUM; i++)
    {
        buffer[i] = 0;
    }
}

void setArrowUp(void)
{
    clearBuffer();
    buffer[0] = 0x18;
    buffer[1] = 0x3C;
    buffer[2] = 0x7E;
    buffer[3] = 0xFF;
    buffer[4] = 0xFF;
    buffer[5] = 0x00;
    buffer[6] = 0x00;
    buffer[7] = 0x00;
}

void setArrowDown(void)
{
    clearBuffer();
    buffer[0] = 0x00;
    buffer[1] = 0x00;
    buffer[2] = 0x00;
    buffer[3] = 0xFF;
    buffer[4] = 0xFF;
    buffer[5] = 0x7E;
    buffer[6] = 0x3C;
    buffer[7] = 0x18;
}

void setArrowLeft(void)
{
    clearBuffer();
    buffer[0] = 0x18;
    buffer[1] = 0x18;
    buffer[2] = 0x18;
    buffer[3] = 0xFF;
    buffer[4] = 0xFF;
    buffer[5] = 0x18;
    buffer[6] = 0x18;
    buffer[7] = 0x18;
}

void setArrowRight(void)
{
    clearBuffer();
    buffer[0] = 0x18;
    buffer[1] = 0x18;
    buffer[2] = 0x18;
    buffer[3] = 0xFF;
    buffer[4] = 0xFF;
    buffer[5] = 0x06;
    buffer[6] = 0x06;
    buffer[7] = 0x06;
}

void setQuestionMark(void)
{
    clearBuffer();
    buffer[0] = 0x3C;
    buffer[1] = 0x42;
    buffer[2] = 0x81;
    buffer[3] = 0x81;
    buffer[4] = 0x81;
    buffer[5] = 0x42;
    buffer[6] = 0x3C;
    buffer[7] = 0x00;
}

void setExpression(uint8_t expression)
{
    switch (expression)
    {
        case 1:
            setArrowUp();
            break;
        case 2:
            setArrowDown();
            break;
        case 3:
            setArrowLeft();
            break;
        case 4:
            setArrowRight();
            break;
        default:
            setQuestionMark();
            break;
    }
}

本代码假定您已经熟悉串口通信和 MAX7219 驱动器。如果您还没有这方面的经验，可以参考相关的教程。此外，此代码是基于 STM32 的标准库实现的。如果您使用其他的开发板或库，可能需要进行适当的修改。