5、5 字符设备驱动程序_查询方式的按键驱动程序

一、编写驱动程序

#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>
#include <asm/arch/regs-gpio.h>
#include <asm/hardware.h>

static struct class *seconddrv_class;
static struct class_device	*seconddrv_class_dev;

volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;

volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;

static int second_drv_open(struct inode *inode, struct file *file)
{
	/* 配置GPF0,2为输入引脚 */
	*gpfcon &= ~((0x3<<(0*2)) | (0x3<<(2*2)));

	/* 配置GPG3,11为输入引脚 */
	*gpgcon &= ~((0x3<<(3*2)) | (0x3<<(11*2)));

	return 0;
}

ssize_t second_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
	/* 返回4个引脚的电平 */
	unsigned char key_vals[4];
	int regval;

	if (size != sizeof(key_vals))
		return -EINVAL;

	/* 读GPF0,2 */
	regval = *gpfdat;
	key_vals[0] = (regval & (1<<0)) ? 1 : 0;
	key_vals[1] = (regval & (1<<2)) ? 1 : 0;
	

	/* 读GPG3,11 */
	regval = *gpgdat;
	key_vals[2] = (regval & (1<<3)) ? 1 : 0;
	key_vals[3] = (regval & (1<<11)) ? 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,    /* 这是一个宏，推向编译模块时自动创建的__this_module变量 */
    .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");

	seconddrv_class_dev = class_device_create(seconddrv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */

	gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);
	gpfdat = gpfcon + 1;

	gpgcon = (volatile unsigned long *)ioremap(0x56000060, 16);
	gpgdat = gpgcon + 1;

	return 0;
}

static void second_drv_exit(void)
{
	unregister_chrdev(major, "second_drv");
	class_device_unregister(seconddrv_class_dev);
	class_destroy(seconddrv_class);
	iounmap(gpfcon);
	iounmap(gpgcon);
	return 0;
}


module_init(second_drv_init);

module_exit(second_drv_exit);

MODULE_LICENSE("GPL");

二、编写测试程序

#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[4];
	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]) //只要有一个等于0就说明按键被按下
		{
			printf("%04d key pressed: %d %d %d %d\n", cnt++, key_vals[0], key_vals[1], key_vals[2], key_vals[3]);
		}
	}
	
	return 0;
}

三、运行
在主机上：


在开发板上：

./seconddrvtest

在后台运行：
./secondrvtest &
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可以看出轮询方式， 死循环， 占用CPU