基于fs4412的Linux实验，实现电位器模拟烟雾浓度，设置一个浓度上限值，当采集值超过上限值时，LED开始闪烁，蜂鸣器响，当低于上限制时灯灭，蜂鸣器不响。原理是什么，怎么去实现，给出应用程序代码及编译文件和驱动程序代码及编译文件

这个实验需要基于fs4412开发板，使用ADC读取电位器的模拟信号，然后根据给定的浓度上限值进行比较，控制LED和蜂鸣器的状态。

具体步骤如下：

1. 连接电位器，将其接到fs4412开发板的ADC引脚上。

2. 编写应用程序代码，使用ADC驱动程序读取电位器的模拟信号，并将其转换为浓度值进行比较。如果浓度值超过上限值，则控制LED开始闪烁，蜂鸣器响；否则，LED熄灭，蜂鸣器停止响。

下面是应用程序代码示例：

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/ioctl.h>
#include <linux/types.h>
#include <linux/spi/spidev.h>
#include <stdint.h>
#include <string.h>

#define ADC_DEV_PATH "/dev/adc"

#define LED_OFF "0"
#define LED_ON "1"

#define BUZZER_OFF "0"
#define BUZZER_ON "1"

#define MAX_CONCENTRATION 500

int main(int argc, char **argv)
{
    int fd, ret;
    uint16_t adc_value;
    float concentration;
    char led_status[2], buzzer_status[2];

    fd = open(ADC_DEV_PATH, O_RDONLY);
    if (fd < 0) {
        printf("Failed to open ADC device %s\n", ADC_DEV_PATH);
        return -1;
    }

    while (1) {
        ret = read(fd, &adc_value, sizeof(adc_value));
        if (ret < 0) {
            printf("Failed to read ADC value\n");
            break;
        }

        concentration = adc_value * 5.0 / 4096 * 100;
        printf("Concentration: %.2f mg/m3\n", concentration);

        if (concentration > MAX_CONCENTRATION) {
            printf("Warning: Concentration exceeds the limit!\n");
            sprintf(led_status, LED_ON);
            sprintf(buzzer_status, BUZZER_ON);
        } else {
            sprintf(led_status, LED_OFF);
            sprintf(buzzer_status, BUZZER_OFF);
        }

        // Control LED and buzzer
        // ...

        usleep(500000);
    }

    close(fd);

    return 0;
}

3. 编写驱动程序代码，使用ADC模块进行模拟信号的读取，并将其转换为数字值返回给应用程序。

下面是驱动程序代码示例：

#include <linux/init.h>
#include <linux/module.h>
#include <linux/kernel.h>
#include <linux/fs.h>
#include <linux/cdev.h>
#include <linux/device.h>
#include <linux/io.h>
#include <linux/uaccess.h>

#define ADC_BASE_ADDR 0x13930000

#define ADC_CONTROL 0x00
#define ADC_CONFIG 0x04
#define ADC_DATA 0x08

#define ADC_CONFIG_VREF_EN BIT(7)

#define ADC_CONTROL_EN BIT(0)
#define ADC_CONTROL_START BIT(1)

static dev_t adc_dev;
static struct cdev adc_cdev;
static struct class *adc_class;
static struct device *adc_device;

static void __iomem *adc_base;

static int adc_open(struct inode *inode, struct file *filp)
{
    void __iomem *regs;

    regs = ioremap(ADC_BASE_ADDR, SZ_4K);
    if (!regs) {
        printk(KERN_ERR "Failed to map ADC registers\n");
        return -ENOMEM;
    }

    // Enable VREF
    writel(ADC_CONFIG_VREF_EN, regs + ADC_CONFIG);

    // Enable ADC
    writel(ADC_CONTROL_EN, regs + ADC_CONTROL);

    adc_base = regs;

    return 0;
}

static int adc_release(struct inode *inode, struct file *filp)
{
    void __iomem *regs = adc_base;

    // Disable ADC
    writel(0, regs + ADC_CONTROL);

    // Disable VREF
    writel(0, regs + ADC_CONFIG);

    iounmap(regs);

    return 0;
}

static ssize_t adc_read(struct file *filp, char __user *buf, size_t count, loff_t *f_pos)
{
    void __iomem *regs = adc_base;
    uint16_t data;

    // Start ADC conversion
    writel(ADC_CONTROL_START, regs + ADC_CONTROL);

    // Wait for conversion to complete
    while (!(readl(regs + ADC_CONTROL) & BIT(2)));

    // Read converted value
    data = readl(regs + ADC_DATA) & 0x0fff;

    if (copy_to_user(buf, &data, sizeof(data))) {
        printk(KERN_ERR "Failed to copy ADC value to user space\n");
        return -EFAULT;
    }

    return sizeof(data);
}

static struct file_operations adc_fops = {
    .owner = THIS_MODULE,
    .open = adc_open,
    .release = adc_release,
    .read = adc_read,
};

static int __init adc_init(void)
{
    int ret;

    ret = alloc_chrdev_region(&adc_dev, 0, 1, "adc");
    if (ret < 0) {
        printk(KERN_ERR "Failed to allocate ADC device number\n");
        return ret;
    }

    cdev_init(&adc_cdev, &adc_fops);
    ret = cdev_add(&adc_cdev, adc_dev, 1);
    if (ret < 0) {
        printk(KERN_ERR "Failed to add ADC device\n");
        goto err_cdev_add;
    }

    adc_class = class_create(THIS_MODULE, "adc");
    if (IS_ERR(adc_class)) {
        printk(KERN_ERR "Failed to create ADC class\n");
        ret = PTR_ERR(adc_class);
        goto err_class_create;
    }

    adc_device = device_create(adc_class, NULL, adc_dev, NULL, "adc");
    if (IS_ERR(adc_device)) {
        printk(KERN_ERR "Failed to create ADC device\n");
        ret = PTR_ERR(adc_device);
        goto err_device_create;
    }

    printk(KERN_INFO "ADC driver initialized\n");

    return 0;

err_device_create:
    class_destroy(adc_class);
err_class_create:
    cdev_del(&adc_cdev);
err_cdev_add:
    unregister_chrdev_region(adc_dev, 1);

    return ret;
}

static void __exit adc_exit(void)
{
    device_destroy(adc_class, adc_dev);
    class_destroy(adc_class);
    cdev_del(&adc_cdev);
    unregister_chrdev_region(adc_dev, 1);

    printk(KERN_INFO "ADC driver exited\n");
}

module_init(adc_init);
module_exit(adc_exit);

MODULE_AUTHOR("Your Name");
MODULE_DESCRIPTION("ADC Driver");
MODULE_LICENSE("GPL");

4. 编译驱动程序代码并加载到fs4412开发板中。

$ make ARCH=arm CROSS_COMPILE=arm-linux-gnueabihf- -C /path/to/linux-source M=$(pwd) modules
$ scp adc.ko root@192.168.1.100:/root/
$ ssh root@192.168.1.100
# insmod adc.ko

5. 编译应用程序代码并运行。

$ arm-linux-gnueabihf-gcc -o app app.c
$ scp app root@192.168.1.100:/root/
$ ssh root@192.168.1.100
# ./app