字符设备驱动程序之查询方式的按键驱动程序

来源：互联网发布：淘宝为什么不卖烟编辑：程序博客网时间：2024/06/05 17:46

这节比较简单，就是实现一个用查询方式实现的按键驱动。
还是按写驱动的几个步骤来编写：
① 写出操作的框架；
② 初始化file_operations；
③在入口函数中注册驱动；
④ 实现硬件操作；
4.1 在open()方法中进行配置
4.2 在read()方法中返回引脚状态
4.3 在入口函数中进行地址映射
驱动程序代码 keys_drv.c 如下:

#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 *gpgcon;volatile unsigned long *gpgdat;static int second_drv_open(struct inode *inode, struct file *file){/* K1,K2,K3,K4对应GPG0，GPG3，GPG5，GPG6配置GPG0，GPG3，GPG5，GPG6为输入引脚 */*gpgcon &= ~((0x3<<(0*2)) | (0x3<<(3*2)) | (0x3<<(5*2)) | (0x3<<(6*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)) //传入的大小不是我们要求返回的大小，就返回错误return -EINVAL;regval = *gpgdat;key_vals[0] = (regval & (1<<0)) ? 1 : 0;key_vals[1] = (regval & (1<<3)) ? 1 : 0;key_vals[2] = (regval & (1<<5)) ? 1 : 0;key_vals[3] = (regval & (1<<6)) ? 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 */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(gpgcon);return 0;}module_init(second_drv_init);module_exit(second_drv_exit);MODULE_LICENSE("GPL");

Makefile的编写也很简单：

KERN_DIR = /work/system/linux-2.6.22.6all:make -C $(KERN_DIR) M=`pwd` modules clean:make -C $(KERN_DIR) M=`pwd` modules cleanrm -rf modules.orderobj-m+= second_drv.o         #只要改一下目标就可以了

接下来，写测试程序：

#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>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]){printf("%04d key pressed: %d %d %d %d\n", cnt++, key_vals[0], key_vals[1], key_vals[2], key_vals[3]);}}return 0;}

平时是高电平，按下时是低电平。这里又不断查询的方式来读出键值。

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