S5PV210（TQ210）学习笔记——按键驱动程序

经过前面的配置&＃xff0c;S5PV210开发已经可以成功进入Linux控制台了&＃xff0c;那么&＃xff0c;有了这个环境就可以开始学习Linux驱动的编写和测试了。学习Linux设备驱动&＃xff0c;通常是从字符设备驱动开始。由于linux驱动开发具有比较系统的体系结构&＃xff0c;我很难在一篇文章中阐述其开发思路&＃xff0c;为了简单起见&＃xff0c;从本文开始&＃xff0c;自行编写的驱动将直接附上代码&＃xff0c;对开发过程中感触比较深的地方稍作陈述。

我写的第一个驱动程序是Led的&＃xff0c;但是感觉没有必要发出来了&＃xff0c;S5PV210&＃xff08;TQ210&＃xff09;的按键驱动程序源码&＃xff0c;仅供参考&＃xff1a;

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include static dev_t devno;
static struct cdev cdev;
static struct class* buttons_class;
static struct device* buttons_device;static wait_queue_head_t button_waitq;static volatile int pressed &＃61; 0;
static unsigned char key_val;struct key_desc{unsigned int pin;unsigned char value;
};static struct key_desc key_descs[8] &＃61; {[0] &＃61; {.pin &＃61; S5PV210_GPH0(0),.value &＃61; 0x00,},[1] &＃61; {.pin &＃61; S5PV210_GPH0(1),.value &＃61; 0x01,},[2] &＃61; {.pin &＃61; S5PV210_GPH0(2),.value &＃61; 0x02,},[3] &＃61; {.pin &＃61; S5PV210_GPH0(3),.value &＃61; 0x03,},[4] &＃61; {.pin &＃61; S5PV210_GPH0(4),.value &＃61; 0x04,},[5] &＃61; {.pin &＃61; S5PV210_GPH0(5),.value &＃61; 0x05,},[6] &＃61; {.pin &＃61; S5PV210_GPH2(6),.value &＃61; 0x06,},[7] &＃61; {.pin &＃61; S5PV210_GPH2(7),.value &＃61; 0x07,},
};static irqreturn_t buttons_irq(int irq, void *dev_id){volatile struct key_desc *key &＃61; (volatile struct key_desc *)dev_id;if(gpio_get_value(key->pin)){key_val &＃61; key->value|0x80;}else{key_val &＃61; key->value;}pressed &＃61; 1;wake_up_interruptible(&button_waitq);return IRQ_RETVAL(IRQ_HANDLED);
}static int buttons_open(struct inode *inode, struct file *file){int ret;ret &＃61; request_irq(IRQ_EINT(0), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key1", &key_descs[0]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(1), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key2", &key_descs[1]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(2), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key3", &key_descs[2]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(3), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key4", &key_descs[3]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(4), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key5", &key_descs[4]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(5), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key6", &key_descs[5]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(22), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key7", &key_descs[6]);if(ret)return ret;ret &＃61; request_irq(IRQ_EINT(23), buttons_irq, IRQ_TYPE_EDGE_BOTH, "key8", &key_descs[7]);if(ret)return ret;return 0;
}static ssize_t buttons_read(struct file * file, char __user *data, size_t count, loff_t *loff){if(count !&＃61; 1){printk(KERN_ERR "The driver can only give one key value once!\n");return -ENOMEM;}wait_event_interruptible(button_waitq, pressed);pressed &＃61; 0;if(copy_to_user(data, &key_val, 1)){printk(KERN_ERR "The driver can not copy the data to user area!\n");return -ENOMEM;}return 0;
}static int buttons_close(struct inode *inode, struct file *file){free_irq(IRQ_EINT(0), &key_descs[0]);free_irq(IRQ_EINT(1), &key_descs[1]); free_irq(IRQ_EINT(2), &key_descs[2]);free_irq(IRQ_EINT(3), &key_descs[3]);free_irq(IRQ_EINT(4), &key_descs[4]);free_irq(IRQ_EINT(5), &key_descs[5]);free_irq(IRQ_EINT(22), &key_descs[6]);free_irq(IRQ_EINT(23), &key_descs[7]);return 0;
}struct file_operations buttons_ops &＃61; {.open &＃61; buttons_open,.read &＃61; buttons_read,.release &＃61; buttons_close,
};int buttons_init(void){int ret;cdev_init(&cdev, &buttons_ops);cdev.owner &＃61; THIS_MODULE;ret &＃61; alloc_chrdev_region(&devno, 0, 1, "buttons");if(ret){printk(KERN_ERR "alloc char device region faild!\n");return ret;}ret &＃61; cdev_add(&cdev, devno, 1);if(ret){printk(KERN_ERR "add char device faild!\n");goto add_error;}buttons_class &＃61; class_create(THIS_MODULE, "buttonsdrv");if(IS_ERR(buttons_class)){printk(KERN_ERR "create class error!\n");goto class_error;}buttons_device &＃61; device_create(buttons_class, NULL, devno, NULL, "buttons");if(IS_ERR(buttons_device)){printk(KERN_ERR "create buttons device error!\n");goto device_error;}init_waitqueue_head(&button_waitq);return 0;device_error:class_destroy(buttons_class);
class_error:cdev_del(&cdev);
add_error:unregister_chrdev_region(devno,1);return -ENODEV;
}void buttons_exit(void){device_destroy(buttons_class, devno);class_destroy(buttons_class);cdev_del(&cdev);unregister_chrdev_region(devno, 1);
}module_init(buttons_init);
module_exit(buttons_exit);
MODULE_LICENSE("GPL");


测试程序代码&＃xff1a;

#include
#include int main(){int fd &＃61; open("/dev/buttons", O_RDWR);if(fd <0){printf("open error");;return 0;}unsigned char key;while(1){read(fd, &key, 1);printf("The key &＃61; %x\n", key);}close(fd);
}

相比轮询方式的按键驱动程序&＃xff0c;中断方式编写的按键驱动程序可以很大程度上节省CPU资源&＃xff0c;因此&＃xff0c;推荐使用中断方式。

但是&＃xff0c;这种方式有个弊端&＃xff0c;如果一直接收不到按键&＃xff0c;程序就会永远阻塞在这里&＃xff0c;幸运的是&＃xff0c;linux内核提供了poll机制&＃xff0c;可以设置延迟时间&＃xff0c;如果在这个时间内受到按键消息则取得键值&＃xff0c;反之则超时退出。使内核支持poll非常简单&＃xff0c;为file_operations的poll成员提供poll处理函数即可。

使内核支持poll还需要以下几步&＃xff1a;

添加poll头文件

编写poll处理函数&＃xff1a;

static unsigned buttons_poll(struct file *file, poll_table *wait){unsigned int mask &＃61; 0;poll_wait(file, &button_waitq, wait);if (pressed)mask |&＃61; POLLIN | POLLRDNORM;return mask;
}

将poll处理函数添加给file_operations&＃xff1a;

.poll &＃61; buttons_poll,

这样&＃xff0c;驱动程序就支持poll机制了。下面是poll方式的测试程序&＃xff1a;

#include
#include
#include
#include
#include int main(int argc, char **argv){int fd;unsigned char key_val;int ret;struct pollfd fds[1];fd &＃61; open("/dev/buttons", O_RDWR);if (fd <0){printf("can&＃39;t open!\n");}fds[0].fd &＃61; fd;fds[0].events &＃61; POLLIN;while (1){ret &＃61; poll(fds, 1, 5000);if (ret &＃61;&＃61; 0){printf("time out\n");}else{read(fd, &key_val, 1);printf("key_val &＃61; 0x%x\n", key_val);}}return 0;
}

这样按键驱动程序就完成了。如果您在编写测试阶段发现了其他问题&＃xff0c;欢迎留言讨论。