poll机制,就是一种查询机制--给定一段时间,如果在这段时间内有按键按下,则立刻返回键值;如果在这段时间里没有按键按下,则处于休眠状态,如果这段时间到了就会返回。
1. poll > sys_poll > do_sys_poll > poll_initwait,poll_initwait函数注册一下回调函数__pollwait,它就是我们的驱动程序执行poll_wait时,真正被调用的函数。
2. 接下来执行file->f_op->poll,即我们驱动程序里自己实现的poll函数
它会调用poll_wait把自己挂入某个队列,这个队列也是我们的驱动自己定义的;
它还判断一下设备是否就绪。
3. 如果设备未就绪,do_sys_poll里会让进程休眠一定时间
4. 进程被唤醒的条件有2:一是上面说的“一定时间”到了,二是被驱动程序唤醒。驱动程序发现条件就绪时,就把“某个队列”上挂着的进程唤醒,这个队列,就是前面通过poll_wait把本进程挂过去的队列。
5. 如果驱动程序没有去唤醒进程,那么chedule_timeout(__timeou)超时后,会重复2、3动作,直到应用程序的poll调用传入的时间到达。
- #include <linux/module.h>
- #include <linux/kernel.h>
- #include <linux/fs.h>
- #include <linux/init.h>
- #include <linux/delay.h>
- #include <linux/irq.h>
- #include <asm/uaccess.h>
- #include <asm/irq.h>
- #include <asm/io.h>
- #include <asm/arch/regs-gpio.h>
- #include <asm/hardware.h>
- #include <linux/poll.h>
- static struct class *forthdrv_class;
- static struct class_device *forthdrv_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);
- /* 中断事件标志, 中断服务程序将它置1,forth_drv_read将它清0 */
- static volatile int ev_press = 0;
- struct pin_desc{
- unsigned int pin;
- unsigned int key_val;
- };
- /* 键值: 按下时, 0x01, 0x02, 0x03, 0x04 */
- /* 键值: 松开时, 0x81, 0x82, 0x83, 0x84 */
- static unsigned char key_val;
- struct pin_desc pins_desc[4] = {
- {S3C2410_GPF0, 0x01},
- {S3C2410_GPF2, 0x02},
- {S3C2410_GPG3, 0x03},
- {S3C2410_GPG11, 0x04},
- };
- /*
- * 确定按键值
- */
- 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)
- {
- /* 松开 */
- key_val = 0x80 | pindesc->key_val;
- }
- else
- {
- /* 按下 */
- key_val = pindesc->key_val;
- }
- ev_press = 1; /* 表示中断发生了 */
- wake_up_interruptible(&button_waitq); /* 唤醒休眠的进程 */
-
- return IRQ_RETVAL(IRQ_HANDLED);
- }
- static int forth_drv_open(struct inode *inode, struct file *file)
- {
- /* 配置GPF0,2为输入引脚 */
- /* 配置GPG3,11为输入引脚 */
- 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 forth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos)
- {
- if (size != 1)
- return -EINVAL;
- /* 如果没有按键动作, 休眠 */
- wait_event_interruptible(button_waitq, ev_press);
- /* 如果有按键动作, 返回键值 */
- copy_to_user(buf, &key_val, 1);
- ev_press = 0;
-
- return 1;
- }
- int forth_drv_close(struct inode *inode, struct file *file)
- {
- 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]);
- return 0;
- }
- static unsigned forth_drv_poll(struct file *file, poll_table *wait)
- {
- unsigned int mask = 0;
- poll_wait(file, &button_waitq, wait); // 不会立即休眠
- if (ev_press)
- mask |= POLLIN | POLLRDNORM;
- return mask;
- }
- 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 = forth_drv_open,
- .read = forth_drv_read,
- .release = forth_drv_close,
- .poll = forth_drv_poll,
- };
- int major;
- static int forth_drv_init(void)
- {
- major = register_chrdev(0, "forth_drv", &sencod_drv_fops);
- forthdrv_class = class_create(THIS_MODULE, "forth_drv");
- forthdrv_class_dev = class_device_create(forthdrv_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 forth_drv_exit(void)
- {
- unregister_chrdev(major, "forth_drv");
- class_device_unregister(forthdrv_class_dev);
- class_destroy(forthdrv_class);
- iounmap(gpfcon);
- iounmap(gpgcon);
- return 0;
- }
- module_init(forth_drv_init);
- module_exit(forth_drv_exit);
- MODULE_LICENSE("GPL");
poll的用法可以在linux终端下通过命令man poll来查询。
测试程序:
- #include <sys/types.h>
- #include <sys/stat.h>
- #include <fcntl.h>
- #include <stdio.h>
- #include <poll.h>
- /* forthdrvtest
- */
- int main(int argc, char **argv)
- {
- int fd;
- unsigned char key_val;
- int ret;
- struct pollfd fds[1];
-
- fd = open("/dev/buttons", O_RDWR);
- if (fd < 0)
- {
- printf("can't open!\n");
- }
- fds[0].fd = fd;
- fds[0].events = POLLIN;
- while (1)
- {
- ret = poll(fds, 1, 5000);
- if (ret == 0) // 等待5s如果没有按键按下返回值为0,则打印超时并退出
- {
- printf("time out\n");
- }
- else
- {
- read(fd, &key_val, 1); // 在5s内有按键按下立即返回按键值。
- printf("key_val = 0x%x\n", key_val);
- }
- }
-
- return 0;
- }
阅读(1410) | 评论(0) | 转发(0) |