如何用MFRC522 RFID模块做一个简易的充值和消费系统：按键盘上的字母键“R”，进入充值功能，可输入充值金额，充值功能后显示卡上余额；按键盘上的字母键“C”，进入消费功能，可输入消费金额，扣除消费金额后显示卡上余额。可以简要回答

使用MFRC522 RFID模块做一个简易的充值和消费系统，可以按照以下步骤进行：

1. 初始化MFRC522 RFID模块和LCD1602屏幕，设置好读卡参数和显示参数。

2. 实现一个循环结构，不断读取RFID卡片，判断卡片类型并获取卡片信息，例如卡号、余额等。

3. 当按下键盘上的字母键“R”时，进入充值功能，提示用户输入充值金额，并将余额加上充值金额后更新到卡片中，并显示卡上余额。

4. 当按下键盘上的字母键“C”时，进入消费功能，提示用户输入消费金额，并将余额减去消费金额后更新到卡片中，并显示卡上余额。

以下是一个示例代码：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <rtthread.h>
#include <rtdevice.h>
#include <board.h>
#include <drv_gpio.h>
#include <drv_spi.h>
#include <drv_lcd1602.h>
#include <drv_mfrc522.h>

#define SPI_BUS_NAME        "spi1"          // SPI总线名称
#define RC522_DEV_NAME      "rc522"         // MFRC522 RFID模块设备名称
#define LCD_DEV_NAME        "lcd"           // LCD1602屏幕设备名称
#define LCD_ROW             2               // LCD1602屏幕行数
#define LCD_COLUMN          16              // LCD1602屏幕列数
#define MAX_BALANCE         10000           // 最大余额
#define RC522_KEY_R         0x52            // “R”键的键值
#define RC522_KEY_C         0x43            // “C”键的键值

static rt_device_t rc522_dev;              // MFRC522 RFID模块设备对象
static rt_device_t lcd_dev;                // LCD1602屏幕设备对象
static char lcd_buffer[LCD_ROW][LCD_COLUMN + 1]; // LCD1602屏幕缓冲区
static rt_uint8_t card_uid[MFRC522_MAX_UID_LENGTH]; // 卡片UID
static rt_uint8_t card_uid_len;             // 卡片UID长度
static rt_uint32_t card_balance = 0;        // 卡片余额

static void rc522_thread_entry(void *parameter)
{
    rt_uint8_t key_value;
    rt_uint8_t sector_key[MFRC522_KEY_LENGTH] = {0xFF, 0xFF, 0xFF, 0xFF, 0xFF, 0xFF};
    rt_uint8_t block_data[MFRC522_BLOCK_LENGTH];
    rt_uint8_t trailer_data[MFRC522_BLOCK_LENGTH];
    rt_uint8_t trailer_addr;
    rt_uint8_t block_addr;
    rt_err_t ret;

    while (1)
    {
        // 等待卡片进入感应区
        if (rt_device_control(rc522_dev, MFRC522_CMD_REQA, RT_NULL) == RT_EOK)
        {
            // 获取卡片UID
            card_uid_len = sizeof(card_uid);
            if (rt_device_control(rc522_dev, MFRC522_CMD_ANTICOLL, card_uid) == RT_EOK)
            {
                // 选择卡片
                ret = rt_device_control(rc522_dev, MFRC522_CMD_SELECT, card_uid);
                if (ret == RT_EOK)
                {
                    // 验证卡片密码
                    rt_memcpy(trailer_data, sector_key, sizeof(sector_key));
                    trailer_addr = 3 * 4 + 3;
                    ret = rt_device_control(rc522_dev, MFRC522_CMD_AUTH, &trailer_addr, trailer_data);
                    if (ret == RT_EOK)
                    {
                        // 读取卡片余额
                        block_addr = 3 * 4 + 1;
                        ret = rt_device_read(rc522_dev, block_addr, block_data, sizeof(block_data));
                        if (ret == sizeof(block_data))
                        {
                            card_balance = (block_data[0] << 24) | (block_data[1] << 16) | (block_data[2] << 8) | block_data[3];
                        }
                    }
                }
            }
        }

        // 检测按键
        key_value = rt_device_read(rc522_dev, MFRC522_REG_FIFO_DATA, RT_NULL, 0);
        if (key_value == RC522_KEY_R)
        {
            // 进入充值功能
            rt_kprintf("Enter recharge function.\n");

            // 提示用户输入充值金额
            rt_device_control(lcd_dev, LCD1602_CMD_CLEAR_SCREEN, RT_NULL);
            snprintf(lcd_buffer[0], LCD_COLUMN + 1, "Recharge:        ");
            rt_device_write(lcd_dev, 0, lcd_buffer[0], strlen(lcd_buffer[0]));
            snprintf(lcd_buffer[1], LCD_COLUMN + 1, "Balance: %4d  ", card_balance);
            rt_device_write(lcd_dev, 0, lcd_buffer[1], strlen(lcd_buffer[1]));
            rt_device_control(lcd_dev, LCD1602_CMD_SET_CURSOR, (void *)0x40);

            // 等待用户输入充值金额
            rt_uint32_t recharge_amount = 0;
            while (1)
            {
                key_value = rt_device_read(rc522_dev, MFRC522_REG_FIFO_DATA, RT_NULL, 0);
                if (key_value >= '0' && key_value <= '9')
                {
                    rt_kprintf("Input recharge amount: %c\n", key_value);
                    recharge_amount = recharge_amount * 10 + (key_value - '0');

                    snprintf(lcd_buffer[0], LCD_COLUMN + 1, "Recharge: %4d    ", recharge_amount);
                    rt_device_write(lcd_dev, 0, lcd_buffer[0], strlen(lcd_buffer[0]));
                    rt_device_control(lcd_dev, LCD1602_CMD_SET_CURSOR, (void *)0x40);
                }
                else if (key_value == RC522_KEY_C)
                {
                    break;
                }
            }

            // 更新卡片余额
            if (recharge_amount > 0)
            {
                card_balance += recharge_amount;
                if (card_balance > MAX_BALANCE)
                {
                    card_balance = MAX_BALANCE;
                }

                // 写入卡片余额
                block_addr = 3 * 4 + 1;
                block_data[0] = (card_balance >> 24) & 0xFF;
                block_data[1] = (card_balance >> 16) & 0xFF;
                block_data[2] = (card_balance >> 8) & 0xFF;
                block_data[3] = card_balance & 0xFF;
                ret = rt_device_write(rc522_dev, block_addr, block_data, sizeof(block_data));
                if (ret == sizeof(block_data))
                {
                    rt_kprintf("Recharge success, balance: %d.\n", card_balance);
                }
                else
                {
                    rt_kprintf("Failed to write balance.\n");
                }
            }

            // 显示卡片余额
            rt_device_control(lcd_dev, LCD1602_CMD_CLEAR_SCREEN, RT_NULL);
            snprintf(lcd_buffer[0], LCD_COLUMN + 1, "Recharge: %4d    ", recharge_amount);
            rt_device_write(lcd_dev, 0, lcd_buffer[0], strlen(lcd_buffer[0]));
            snprintf(lcd_buffer[1], LCD_COLUMN + 1, "Balance: %4d  ", card_balance);
            rt_device_write(lcd_dev, 0, lcd_buffer[1], strlen(lcd_buffer[1]));
        }
        else if (key_value == RC522_KEY_C)
        {
            // 进入消费功能
            rt_kprintf("Enter consumption function.\n");

            // 提示用户输入消费金额
            rt_device_control(lcd_dev, LCD1602_CMD_CLEAR_SCREEN, RT_NULL);
            snprintf(lcd_buffer[0], LCD_COLUMN + 1, "Consumption:      ");
            rt_device_write(lcd_dev, 0, lcd_buffer[0], strlen(lcd_buffer[0]));
            snprintf(lcd_buffer[1], LCD_COLUMN + 1, "Balance: %4d  ", card_balance);
            rt_device_write(lcd_dev, 0, lcd_buffer[1], strlen(lcd_buffer[1]));
            rt_device_control(lcd_dev, LCD1602_CMD_SET_CURSOR, (void *)0x40);

            // 等待用户输入消费金额
            rt_uint32_t consumption_amount = 0;
            while (1)
            {
                key_value = rt_device_read(rc522_dev, MFRC522_REG_FIFO_DATA, RT_NULL, 0);
                if (key_value >= '0' && key_value <= '9')
                {
                    rt_kprintf("Input consumption amount: %c\n", key_value);
                    consumption_amount = consumption_amount * 10 + (key_value - '0');

                    snprintf(lcd_buffer[0], LCD_COLUMN + 1, "Consumption: %4d ", consumption_amount);
                    rt_device_write(lcd_dev, 0, lcd_buffer[0], strlen(lcd_buffer[0]));
                    rt_device_control(lcd_dev, LCD1602_CMD_SET_CURSOR, (void *)0x40);
                }
                else if (key_value == RC522_KEY_C)
                {
                    break;
                }
            }

            // 更新卡片余额
            if (consumption_amount > 0 && consumption_amount <= card_balance)
            {
                card_balance -= consumption_amount;

                // 写入