韦东山驱动视频笔记——2.字符设备驱动程序之中断方式的按键驱动程序
linux内核版本：linux-2.6.30.4
目的：当有按键按下和松开时，在终端输出不同的键值
原理：假设我们现在已经加载（insmod）了third_drv.ko，当我们进入main函数后，可以打开设备节点"/dev/buttons"，然后进入while循环，接着系统调用read，内核经过一系列的处理，进入到我们的驱动程序的read函数（third_drv_read），这时候如果没有按键按下，应用程序就会停在wait_event_interruptible处休眠，程序就不会向下面跑了，假如在某个时间点我们按下了按键，就会触发中断，调用中断处理函数（buttons_irq），经过读取按键的引脚的电平高低来判断是按下还是松开，然后给key_val赋不同的值，最后唤醒等待队列，然后重新调用wait_event_interruptible，此时ev_press = 1，就不会再休眠，所以可以继续执行，就把按键值返回了用户空间，所以我们的应用程序中的key_val得到了按键值。
1 #include <linux/module.h> 2 #include <linux/kernel.h> 3 #include <linux/fs.h> 4 #include <linux/init.h> 5 #include <linux/delay.h> 6 #include <asm/uaccess.h> 7 #include <asm/irq.h> 8 #include <asm/io.h> 9 #include <linux/device.h> 10 #include <linux/irq.h> 11 #include <linux/interrupt.h> 12 #include <mach/regs-gpio.h> 13 14 15 static struct class *third_drv_class; 16 static struct class_device *third_drv_class_dev; 17 18 static volatile unsigned long *gpfcon; 19 static volatile unsigned long *gpfdat; 20 static int major; 21 22 struct pin_desc 23 { 24 unsigned int pin; 25 unsigned int key_val; 26 }; 27 28 static unsigned char key_val; 29 30 static struct pin_desc pins_desc[4] = 31 { 32 {S3C2410_GPF1, 0x01}, 33 {S3C2410_GPF4, 0x02}, 34 {S3C2410_GPF2, 0x03}, 35 {S3C2410_GPF0, 0x04}, 36 }; 37 38 static DECLARE_WAIT_QUEUE_HEAD(button_waitq); 39 static volatile int ev_press = 0; 40 41 static irqreturn_t buttons_irq(int irq, void *dev_id) 42 { 43 struct pin_desc *pin = (struct pin_desc *)dev_id; 44 unsigned int pinval; 45 pinval = s3c2410_gpio_getpin(pin->pin); 46 47 if (pinval) 48 { 49 //松开 50 key_val = 0x80 | pin->key_val; 51 } 52 else 53 { 54 //按下 55 key_val = pin->key_val; 56 } 57 58 wake_up_interruptible(&button_waitq); 59 ev_press = 1; 60 61 return IRQ_HANDLED; 62 } 63 64 65 static int third_drv_open(struct inode *inode, struct file *file) 66 { 67 request_irq(IRQ_EINT1, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S1", &pins_desc[0]); 68 request_irq(IRQ_EINT4, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S2", &pins_desc[1]); 69 request_irq(IRQ_EINT2, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S3", &pins_desc[2]); 70 request_irq(IRQ_EINT0, buttons_irq, IRQ_TYPE_EDGE_BOTH, "S4", &pins_desc[3]); 71 return 0; 72 } 73 74 75 static ssize_t third_drv_read(struct file *file, char __user *buf, 76 size_t count, loff_t *ppos) 77 { 78 if (count != 1) 79 return -EINVAL; 80 /*如果没有按键动作，休眠*/ 81 wait_event_interruptible(button_waitq, ev_press); 82 83 84 /*如果有按键动作发生，返回键值*/ 85 copy_to_user(buf, &key_val, 1); 86 ev_press = 0; 87 return 1; 88 } 89 90 static int third_drv_release(struct inode *inode, struct file *file) 91 { 92 free_irq(IRQ_EINT1, &pins_desc[0]); 93 free_irq(IRQ_EINT4, &pins_desc[1]); 94 free_irq(IRQ_EINT2, &pins_desc[2]); 95 free_irq(IRQ_EINT0, &pins_desc[3]); 96 return 0; 97 } 98 99 100 static struct file_operations third_fops = { 101 .owner = THIS_MODULE, 102 .open = third_drv_open, 103 .read = third_drv_read, 104 .release = third_drv_release, 105 }; 106 107 int third_init() 108 { 109 int ret; 110 major = register_chrdev(0, "third_drv", &third_fops); 111 third_drv_class = class_create(THIS_MODULE, "third_drv"); 112 device_create(third_drv_class, NULL, MKDEV(major, 0), NULL, "buttons"); 113 114 gpfcon = (volatile unsigned long *)ioremap(0x56000050, 16); 115 gpfdat = gpfcon + 1; 116 117 return 0; 118 } 119 static void third_exit() 120 { 121 unregister_chrdev(major, "third_drv"); 122 device_destroy(third_drv_class, MKDEV(major, 0)); 123 class_destroy(third_drv_class); 124 iounmap(gpfcon); 125 } 126 127 module_init(third_init); 128 module_exit(third_exit); 129 130 MODULE_LICENSE("GPL");
测试程序：
1 #include <sys/types.h> 2 #include <sys/stat.h> 3 #include <fcntl.h> 4 #include <stdio.h> 5 6 /* thirddrvtest 7 */ 8 int main(int argc, char **argv) 9 { 10 int fd; 11 unsigned char key_val; 12 int cnt = 0; 13 14 fd = open("/dev/buttons", O_RDWR); 15 if (fd < 0) 16 { 17 printf("can't open!\n"); 18 } 19 20 while (1) 21 { 22 read(fd, &key_val, 1); 23 printf("key_val === 0x%x\n", key_val); 24 25 } 26 27 return 0; 28 }
运行效果：
