炫耀一下

韦东山的第一期视频基本上已经看完，基本上已经可以在开发板上写一个小的驱动，比如说想知道按下按键的按键号，可以用查询、中断、异步通知等方法。其中，查询是最耗CPU资源的一种方法，可以用中断来改进。不过中断时，应用函数进入休眠，等待中断的唤醒，此过程不能处理其他事。所以说，异步通知是最好的一种方法，它可以由驱动发起，告知应用程序，不影响应用程序做其他事。以下面的例程来说明：

功能：查询按键号

驱动程序：

#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 <linux/sched.h>#include <linux/interrupt.h>#include <linux/device.h>#include <asm/uaccess.h>#include <asm/irq.h>#include <asm/io.h>#include <mach/regs-gpio.h>#include <mach/hardware.h>#include <linux/wait.h>/*按键k1 EINT1.  GPF1按键k2 EINT4.  GPF4按键k3 EINT2.  GPF2按键k4 EINT0.  GPF0GPFCON=0x56000050GPFDAT=0x56000054GPFUP=0x56000058 */static struct class *drv_class;static struct class_device*drv_class_dev;static struct fasync_struct *button_async;volatile unsigned long *gpfcon;volatile unsigned long *gpfdat;static unsigned char key_val;struct pin_desc{unsigned int pin;unsigned int kval;};struct pin_desc pins_desc[4] = {{S3C2410_GPF1, 0x01},{S3C2410_GPF4, 0x02},{S3C2410_GPF2, 0x03},{S3C2410_GPF0, 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->kval;}else{/* 按下 */key_val = pindesc->kval;}kill_fasync(&button_async, SIGIO, POLL_IN);return IRQ_RETVAL(IRQ_HANDLED);}static int fifth_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_EINT1,  buttons_irq, IRQ_TYPE_EDGE_BOTH, "S1", &pins_desc[0]);request_irq(IRQ_EINT4,  buttons_irq, IRQ_TYPE_EDGE_BOTH, "S2", &pins_desc[1]);request_irq(IRQ_EINT2, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S3", &pins_desc[2]);request_irq(IRQ_EINT0, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S4", &pins_desc[3]);return 0;}ssize_t fifth_drv_read(struct file *file, char __user *buf, size_t size, loff_t *ppos){copy_to_user(buf, &key_val, 1);return 1;}static int fifth_drv_fasync (int fd, struct file *filp, int on){printk("driver: fifth_drv_fasync\n");return fasync_helper (fd, filp, on, &button_async);}int fifth_drv_close(struct inode *inode, struct file *file){free_irq(IRQ_EINT1, &pins_desc[0]);free_irq(IRQ_EINT4, &pins_desc[1]);free_irq(IRQ_EINT2, &pins_desc[2]);free_irq(IRQ_EINT0, &pins_desc[3]);fifth_drv_fasync (-1, file, 0);return 0;}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    =  fifth_drv_open,     .read     = fifth_drv_read,   .release =  fifth_drv_close,.fasync = fifth_drv_fasync,};int major;static int fifth_drv_init(void){major = register_chrdev(0, "fifth_drv", &sencod_drv_fops);drv_class = class_create(THIS_MODULE, "fifth_drv");drv_class_dev = device_create(drv_class, NULL, MKDEV(major, 0), NULL, "buttons"); /* /dev/buttons */gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16);gpfdat = gpfcon + 1;return 0;}static void fifth_drv_exit(void){unregister_chrdev(major, "third_drv");device_destroy(drv_class,MKDEV(major,0));class_destroy(drv_class);iounmap(gpfcon);}module_init(fifth_drv_init);module_exit(fifth_drv_exit);MODULE_LICENSE("GPL");

测试程序：

#include <sys/types.h>#include <sys/stat.h>#include <fcntl.h>#include <stdio.h>#include <poll.h>#include <signal.h>#include <sys/types.h>#include <unistd.h>#include <fcntl.h>int fd;void my_signal_fun(int signum){unsigned char val;read(fd,&val,1);printf("keyval:0x%x\n",val);} int main(){ int oflags;signal(SIGIO,my_signal_fun);fd =open("/dev/buttons",O_RDWR);if (fd<0){printf("can't open! \n");}fcntl(fd,F_SETOWN,getpid());oflags =fcntl(fd,F_GETFL);fcntl(fd,F_SETFL,oflags|FASYNC);while(1){sleep(1000);}return 0;  }

在测试程序中，while（1）内可以做任何事，当有按键按下时，在中断处理函数中，读出按键val，并发送SIGIO信号至应用程序，在信号绑定的函数中，读出并显示val值。此过程几乎不消耗CPU资源。

如下图所示