一、異步通知概念：
異步通知是指：一旦裝置就緒，則主動通知應用程式，應用程式根本就不需要查詢裝置狀态，類似于中斷的概念，一個程序收到一個信号與處理器收到一個中斷請求可以說是一樣的。信号是異步的，一個程序不必通過任何操作來等待信号的到達。下面我們就看一下在linux中機制的實作方式。
在Linux中，異步通知是使用信号來實作的，而在Linux，大概有30種信号，比如大家熟悉的ctrl+c的SIGINT信号，程序能夠忽略或者捕獲除過SIGSTOP和SIGKILL的全部信号，當信号背捕獲以後，有相應的signal()函數來捕獲信号，函數原型：sighandler_t signal(int signum, sighandler_t handler);第 一個參數就是指定的信号的值，而第二個參數便是此信号的信号處理函數，當為SIG_IGN,表示信号被忽略，當為SIG_DFL時，表示采用系統的預設方 式來處理該信号。當然，信号處理函數也可以自己定義。當signal()調用成功後，傳回處理函數handler值，調用失敗後傳回SIG_ERR。
二、信号處理要點：
①、注冊信号處理函數：應用注冊
②、發送者：驅動drv
③、接受者：應用app
④、發送方法：kill_fasync (&button_async, SIGIO, POLL_IN);
三、 原子操作：執行過程中不會被别的代碼路徑所中斷的操作
常用原子操作函數：
atomic_t v = ATOMIC_INIT(0); //定義原子變量v并初始化為0
atomic_read(atomic_t *v); //傳回原子變量的值
void atomic_inc(atomic_t *v); //原子變量增加1
void atomic_dec(atomic_t *v); //原子變量減少1
int atomic_dec_and_test(atomic_t *v); //自減操作後測試結果，0傳回真，否則傳回假
四、信号量
1.定義：struct semaphore sem:
2.初始化：void sema_init(struct semaphore *sem, int val);
void init_MUTEX(stuct semaphore *sem); //初始化為0
static DECLARE_MUTEX(button_lock); //定義互斥鎖
3.獲得信号量: void down(struct semaphore *sem);
int down_interruptible(struct semaphore *sem);
int down_trylock(struct semaphore *sem);
4.釋放信号量：
void up(struct semaphore *sem);
五、阻塞：執行裝置操作時若不能獲得資源，則挂起進入休眠狀态，被從排程器的運作隊列移走，直到條件滿足。
非阻塞：執行裝置操作時若不能獲得資源，釋放或查詢等待條件滿足。 ： fd = open("/dev/buttons", O_RDWR | O_NONBLOCK);
六、示例代碼：1.驅動代碼: signal_drv.c ========================================
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
#include
static struct class *signaldrv_class;
static struct class_device *signaldrv_class_dev;
volatile unsigned long *gpfcon;
volatile unsigned long *gpfdat;
volatile unsigned long *gpgcon;
volatile unsigned long *gpgdat;
static DECLARE_WAIT_QUEUE_HEAD(button_waitq);
static volatile int ev_press = 0;
static struct fasync_struct *button_async;
struct pin_desc{
unsigned int pin;
unsigned int key_val;
};
static unsigned char key_val;
struct pin_desc pins_desc[4] = {
{S3C2410_GPF0, 0x01},
{S3C2410_GPF2, 0x02},
{S3C2410_GPG3, 0x03},
{S3C2410_GPG11, 0x04},
};
//static atomic_t canopen = ATOMIC_INIT(1); //定義原子變量并初始化為1
static DECLARE_MUTEX(button_lock); //定義互斥鎖
static irqreturn_t buttons_irq(int irq, void *dev_id)
{
struct pin_desc * pindesc = (struct pin_desc *)dev_id;
unsigned int pinval;
pinval = s3c2410_gpio_getpin(pindesc->pin);
if (pinval)
{
key_val = 0x80 | pindesc->key_val;
}
else
{
key_val = pindesc->key_val;
}
ev_press = 1;
wake_up_interruptible(&button_waitq);
kill_fasync (&button_async, SIGIO, POLL_IN);
return IRQ_RETVAL(IRQ_HANDLED);
}
static int signal_drv_open(struct inode *inode, struct file *file)
{
#if 0
if (!atomic_dec_and_test(&canopen))
{
atomic_inc(&canopen);
return -EBUSY;
}
#endif
if (file->f_flags & O_NONBLOCK)
{
if (down_trylock(&button_lock))
return -EBUSY;
}
else
{
down(&button_lock);
}
request_irq(IRQ_EINT0, buttons_irq, IRQT_BOTHEDGE, "S2", &pins_desc[0]);
request_irq(IRQ_EINT2, buttons_irq, IRQT_BOTHEDGE, "S3", &pins_desc[1]);
request_irq(IRQ_EINT11, buttons_irq, IRQT_BOTHEDGE, "S4", &pins_desc[2]);
request_irq(IRQ_EINT19, buttons_irq, IRQT_BOTHEDGE, "S5", &pins_desc[3]);
return 0;
}
ssize_t signal_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
{
if (size != 1)
return -EINVAL;
if (file->f_flags & O_NONBLOCK)
{
if (!ev_press)
return -EAGAIN;
}
else
{
wait_event_interruptible(button_waitq, ev_press);
}
copy_to_user(buf, &key_val, 1);
ev_press = 0;
return 1;
}
int signal_drv_close(struct inode *inode, struct file *file)
{
//atomic_inc(&canopen);
free_irq(IRQ_EINT0, &pins_desc[0]);
free_irq(IRQ_EINT2, &pins_desc[1]);
free_irq(IRQ_EINT11, &pins_desc[2]);
free_irq(IRQ_EINT19, &pins_desc[3]);
up(&button_lock);
return 0;
}
static unsigned signal_drv_poll(struct file *file, poll_table *wait)
{
unsigned int mask = 0;
poll_wait(file, &button_waitq, wait); // 不會立即休眠
if (ev_press)
mask |= POLLIN | POLLRDNORM;
return mask;
}
static int signal_drv_fasync (int fd, struct file *filp, int on)
{
printk("driver: signal_drv_fasync\n");
return fasync_helper (fd, filp, on, &button_async);
}
static struct file_operations sencod_drv_fops = {
.owner = THIS_MODULE,
.open = signal_drv_open,
.read = signal_drv_read,
.release = signal_drv_close,
.poll = signal_drv_poll,
.fasync = signal_drv_fasync,
};
int major;
static int signal_drv_init(void)
{
major = register_chrdev(0, "signal_drv", &sencod_drv_fops);
signaldrv_class = class_create(THIS_MODULE, "signal_drv");
signaldrv_class_dev = class_device_create(signaldrv_class, NULL, MKDEV(major, 0), NULL, "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 signal_drv_exit(void)
{
unregister_chrdev(major, "signal_drv");
class_device_unregister(signaldrv_class_dev);
class_destroy(signaldrv_class);
iounmap(gpfcon);
iounmap(gpgcon);
return 0;
}
module_init(signal_drv_init);
module_exit(signal_drv_exit);
MODULE_LICENSE("GPL");
2.測試代碼：signaltest.c =============================================
#include
#include
#include
#include
#include
#include
#include
#include
#include
int fd;
void my_signal_fun(int signum)
{
unsigned char key_val;
read(fd, &key_val, 1);
printf("key_val: 0x%x\n", key_val);
}
int main(int argc, char **argv)
{
unsigned char key_val;
int ret;
int Oflags;
//signal(SIGIO, my_signal_fun);
fd = open("/dev/buttons", O_RDWR | O_NONBLOCK);
if (fd < 0)
{
printf("can't open!\n");
return -1;
}
//fcntl(fd, F_SETOWN, getpid());
//Oflags = fcntl(fd, F_GETFL);
//fcntl(fd, F_SETFL, Oflags | FASYNC);
while (1)
{
ret = read(fd, &key_val, 1);
printf("key_val: 0x%x, ret = %d\n", key_val, ret);
sleep(5);
}
return 0;
}
3.Makefile: ================================
KERN_DIR = /work/system/linux-2.6.22.6
all:
make -C $(KERN_DIR) M=`pwd` modules
clean:
make -C $(KERN_DIR) M=`pwd` modules clean
rm -rf modules.order
obj-m += signal_drv.o
rm -rf modules.order
obj-m+= signal_drv.o
