second_drv.c驅動源碼：

#include "linux/device.h"

#include "linux/module.h"

#include "linux/kernel.h"

#include "linux/fs.h"

#include "linux/init.h"

#include "linux/delay.h"

#include "asm/uaccess.h"

#include "asm/irq.h"

#include "asm/io.h"

static struct class *seconddrv_class;

volatile unsigned long *gph2con;

volatile unsigned long *gph2dat;

volatile unsigned long *gph3con;

volatile unsigned long *gph3dat;

static int second_drv_open(struct inode *inode, struct file *file)

{

    // 配置GPH2_3為輸入引腳 

    *gph2con &= ~(0xf<<(3*4));

    // 配置GPH3_0,GPH3_1,GPH3_2,GPH3_3為輸入引腳 

    *gph3con &= ~((0xf<<(0*4)) | (0xf<<(1*4)) | (0xf<<(2*4)) | (0xf<<(3*4)));

    return 0;

}

ssize_t second_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)

{

    // 返回5個引腳的電平 

    unsigned char key_vals[5];

    int regval;

    if (size != sizeof(key_vals))

        return -EINVAL;

    // 讀GPH2_3 

    regval = *gph2dat;

    key_vals[0] = (regval & (1<<3)) ? 1 : 0;    

    // 讀GPH3_0,GPH3_1,GPH3_2,GPH3_3 

    regval = *gph3dat;

    key_vals[1] = (regval & (1<<0)) ? 1 : 0;

    key_vals[2] = (regval & (1<<1)) ? 1 : 0;

    key_vals[3] = (regval & (1<<2)) ? 1 : 0;

    key_vals[4] = (regval & (1<<3)) ? 1 : 0;

    copy_to_user(buf, key_vals, sizeof(key_vals));

    return sizeof(key_vals);

}

static struct file_operations sencod_drv_fops = {

    .owner  =   THIS_MODULE,    // 這是一個宏，推向編譯模塊時自動創建的__this_module變量 

    .open   =   second_drv_open,     

    .read   =   second_drv_read,       

};

int major;

static int second_drv_init(void)

{

    major = register_chrdev(0, "second_drv", &sencod_drv_fops);

    seconddrv_class = class_create(THIS_MODULE, "second_drv");

    device_create(seconddrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); // /dev/buttons 

    gph2con = (volatile unsigned long *)ioremap(0xe0200c40, 16);

    gph2dat = gph2con + 1;

    gph3con = (volatile unsigned long *)ioremap(0xE0200C60, 16);

    gph3dat = gph3con + 1;

    return 0;

}

static void second_drv_exit(void)

{

    unregister_chrdev(major, "second_drv");

    device_destroy(seconddrv_class, MKDEV(major, 0));

    class_destroy(seconddrv_class);

    iounmap(gph2con);

    iounmap(gph3con);

    return 0;

}

module_init(second_drv_init);

module_exit(second_drv_exit);

MODULE_LICENSE("GPL");

====================================================================

seconddrvtest.c測試程序：

#include "sys/types.h"

#include "sys/stat.h"

#include "fcntl.h"

#include "stdio.h"

// seconddrvtest 

int main(int argc, char **argv)

{

    int fd;

    unsigned char key_vals[5];

    int cnt = 0;

    fd = open("/dev/buttons", O_RDWR);

    if (fd < 0)

    {

        printf("can't open!\n");

    }

    while (1)

    {

        read(fd, key_vals, sizeof(key_vals));

        if (!key_vals[0] || !key_vals[1] || !key_vals[2] || !key_vals[3] || !key_vals[4])

        {

            printf("d key pressed: %d %d %d %d %d\n", cnt++, key_vals[0], 

                                                                                             key_vals[1], key_vals[2], 

                                                                                             key_vals[3], key_vals[4]);

        }

    }

    return 0;

}