内核定时器用于按键处理

#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include ccess.h>
#include
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#include
#include

static struct timer_list buttons_timer;

static struct class *sixthdrv_class;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
static struct fasync_struct *button_async;
//static atomic_t canopen = ATOMIC_INIT(1); //定义原子变量并初始化为1
static DECLARE_MUTEX(button_lock); //定义互斥锁

/* 中断事件标志, 中断服务程序将它置1，buttons_timer_read将它清0 */
static volatile int ev_press = 0;//等于0的话就会一直等待
static unsigned char key_val;

struct pin_desc {
unsigned int pin;
unsigned int val;
};
struct pin_desc pins [] = {
{S3C2410_GPG(0),1},
{S3C2410_GPG(3),2},
{S3C2410_GPG(5),3},
{S3C2410_GPG(6),4}
};

static struct pin_desc *irq_pd;

static irqreturn_t buttons_irq(int irq, void *dev_id)
{
/* 10ms后启动定时器 */
/*
原理当触发中断的时候，进入此函数，然后修改定时器的值10ms后
去执行定时器指定的函数，读取键值
*/
irq_pd = (struct pin_desc *)dev_id;//这里为参数传递，因为
//buttons_timer_function里没法得到传入引脚值
mod_timer(&buttons_timer, jiffies+HZ/100);
return IRQ_RETVAL(IRQ_HANDLED);
}

static void buttons_timer_function(unsigned long data)
{
//printk("irqno = %dn" , irqno);
struct pin_desc *pings = irq_pd;

if (pings==NULL)
return -EFAULT;

if(s3c2410_gpio_getpin(pings->pin))//传入pin值
{
/* 松开 */
key_val = 0x80 | pings->val;
}
else
{
/* 按下 */
key_val = pings->val;
}
ev_press = 1; /* 表示中断发生了 */
wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
/*
通过系统函数kill_fasync向进程发送异步IO信号
POLL_IN表示数据可读
*/
kill_fasync (&button_async, SIGIO, POLL_IN);
//return IRQ_RETVAL(IRQ_HANDLED);//这里是一个宏，里面是一个条件判断，最终返回1
}

static int buttons_timer_open(struct inode *inode, struct file *file)
{//S3C2410_GPG(0)

/*
* K1,K2,K3,K4对应GPG0，GPG3，GPG5，GPG6
*/
#if 0
if (!atomic_dec_and_test(&canopen))//自减并判断是否为0，为0返回true，不然返回false
{
atomic_inc(&canopen);//自增
return -EBUSY;
}
#endif

if (file->f_flags & O_NONBLOCK)//以非阻塞方式打开，不成功还是返回
{

//printk(KERN_EMERG "open failedn");
//down_trylock获取信号量不成功不会睡眠而是正常退出
if (down_trylock(&button_lock))//申请信号量，如果成功申请则返回0，不然返回非0
return -EBUSY;//不会导致睡眠
//return 100;
}
else
{
/* 获取信号量 */
down(&button_lock);//如果获取不到信号量，将进入不可中断的睡眠
// down_killable(&button_lock)//如果获取不到信号量,可以杀
// down_interruptible(&button_lock)//如果获取不到信号量,可以中断方式唤醒
}

request_irq(IRQ_EINT8, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K1", &pins[0]);
request_irq(IRQ_EINT11, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K2", &pins[1]);
request_irq(IRQ_EINT13, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K3", &pins[2]);
request_irq(IRQ_EINT14, buttons_irq, IRQ_TYPE_EDGE_BOTH, "K4", &pins[3]);

return 0;
}

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

if (size != 8)//格式控制，如果用户程序传过来的不是1长度，则直接返回
return -EINVAL;
if (file->f_flags & O_NONBLOCK)//非阻塞方式读，没有键值，返回，不会等待
{
if (!ev_press)
return -EAGAIN;
}
else
{
/* 如果没有按键动作, 休眠 */
wait_event_interruptible(button_waitq, ev_press);
}

/* 如果没有按键动作, 休眠 在此就使应用程序休眠，直到有中断来唤醒*/
//wait_event_interruptible(button_waitq, ev_press);//ev_press = 0时休眠
//执行到这，说明已被唤醒,ev_press = 1,所以要清零
ev_press = 0;
copy_to_user(buf, &key_val, 1);

return 1;
}
int buttons_timer_close(struct inode *inode, struct file *file)
{
free_irq(IRQ_EINT8, &pins[0]);
free_irq(IRQ_EINT11, &pins[1]);
free_irq(IRQ_EINT13, &pins[2]);
free_irq(IRQ_EINT14, &pins[3]);
//atomic_inc(&canopen);
up(&button_lock);
return 0;
}
static unsigned buttons_timer_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0; //为0则poll_wait加入队列后进入休眠
poll_wait(file, &button_waitq, wait); // 先加入队列，不会立即休眠

if (ev_press)
mask |= POLLIN | POLLRDNORM;

return mask;//返回非零直接唤醒进程
}
static int buttons_timer_fasync (int fd, struct file *filp, int on)
{
printk("driver: buttons_timer_fasyncn");
return fasync_helper (fd, filp, on, &button_async);//此函数会初始化button_async结构体
}

static struct file_operations buttons_timer_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 = buttons_timer_open,
.read=buttons_timer_read,
.release = buttons_timer_close,
.poll = buttons_timer_poll,
.fasync = buttons_timer_fasync,//注册异步处理函数
};//当应用程序一打开异步模式，就会调用此函数

int major;
static int buttons_timer_init(void)
{

init_timer(&buttons_timer);
buttons_timer.function = buttons_timer_function;
//buttons_timer.expires = 0;
add_timer(&buttons_timer);

major = register_chrdev(0, "buttons_timer", &buttons_timer_fops);

sixthdrv_class = class_create(THIS_MODULE, "buttons_timer");

device_create(sixthdrv_class, NULL, MKDEV(major, 0), NULL, "buttons_timer"); /* /dev/buttons */

return 0;
}

static void buttons_timer_exit(void)
{
unregister_chrdev(major, "buttons_timer");
device_destroy(sixthdrv_class,MKDEV(major, 0));
class_destroy(sixthdrv_class);

}

module_init(buttons_timer_init);

module_exit(buttons_timer_exit);

MODULE_LICENSE("GPL");

这里有一点需要注意，就是关于空指针的问题如：

这里定义static struct pin_desc *irq_pd;指针，但是没给它赋值的话，虽然定时器函数中irq_pd = (struct pin_desc *)dev_id;好像赋了值，但是在struct pin_desc *pings = irq_pd;中再次使用的时候，也会有空指针问题热报错 所以要加入

if (pings==NULL)
return -EFAULT;