|
在嵌入式系統(tǒng)的設(shè)計中，LED一般直接由CPU的GPIO（通用可編程I/O口）控制。GPIO一般由兩組寄存器控制，即一組控制寄存器和一組數(shù)據(jù)寄存器。控制寄存器可設(shè)置GPIO口的工作方式為輸入或是輸出。當(dāng)引腳被設(shè)置為輸出時，向數(shù)據(jù)寄存器的對應(yīng)位寫入1和0會分別在引腳上產(chǎn)生高電平和低電平；當(dāng)引腳設(shè)置為輸入時，讀取數(shù)據(jù)寄存器的對應(yīng)位可獲得引腳上的電平為高或低。
LED設(shè)備介于字符設(shè)備和塊設(shè)備之間我們稱之為misc（雜設(shè)備），其實按linux下的驅(qū)動位置來講還是一種字符設(shè)備。代碼清單1.1給出了Linux下LED的驅(qū)動。
代碼清單1.1 Linux操作系統(tǒng)下LED的驅(qū)動
1 #include .../*包含內(nèi)核中的多個頭文件*/
2 /*設(shè)備結(jié)構(gòu)體*/
3 struct light_dev {
4 struct cdev cdev; /*字符設(shè)備cdev結(jié)構(gòu)體*/
5 unsigned char vaule; /*LED亮?xí)r為1，熄滅時為0，用戶可讀寫此值*/
6 };
7 struct light_dev *light_devp;
8 int light_major = LIGHT_MAJOR;
9 MODULE_AUTHOR("Barry Song <21cnbao@gmail.com>");
10 MODULE_LICENSE("Dual BSD/GPL");
11 /*打開和關(guān)閉函數(shù)*/
12 int light_open(struct inode *inode, struct file *filp)
13 {
14 struct light_dev *dev;
15 /* 獲得設(shè)備結(jié)構(gòu)體指針 */
16 dev = container_of(inode->i_cdev, struct light_dev, cdev);
17 /* 讓設(shè)備結(jié)構(gòu)體作為設(shè)備的私有信息 */
18 filp->private_data = dev;
19 return 0;
20 }
21 int light_release(struct inode *inode, struct file *filp)
22 {
23 return 0;
24 }
25 /*讀寫設(shè)備:可以不需要 */
26 ssize_t light_read(struct file *filp, char __user *buf, size_t count,
27 loff_t *f_pos)
28 {
29 struct light_dev *dev = filp->private_data; /*獲得設(shè)備結(jié)構(gòu)體 */
30 if (copy_to_user(buf, &(dev->value), 1))
31 return -EFAULT;
32 return 1;
33 }
34 ssize_t light_write(struct file *filp, const char __user *buf, size_t count,
35 loff_t *f_pos)
36 {
37 struct light_dev *dev = filp->private_data;
38 if (copy_from_user(&(dev->value), buf, 1))
39 return -EFAULT;
40 /*根據(jù)寫入的值點亮和熄滅LED*/
41 if (dev->value == 1)
42 light_on();
43 else
44 light_off();
45 return 1;
46 }
47 /* ioctl函數(shù) */
48 int light_ioctl(struct inode *inode, struct file *filp, unsigned int cmd,
49 unsigned long arg)
50 {
51 struct light_dev *dev = filp->private_data;
52 switch (cmd) {
53 case LIGHT_ON:
54 dev->value = 1;
55 light_on();
56 break;
57 case LIGHT_OFF:
58 dev->value = 0;
59 light_off();
60 break;
61 default:
62 /* 不能支持的命令 */
63 return -ENOTTY;
64 }
65 return 0;
66 }
67 struct file_operations light_fops = {
68 .owner = THIS_MODULE,
69 .read = light_read,
70 .write = light_write,
71 .ioctl = light_ioctl,
72 .open = light_open,
73 .release = light_release,
74 };
75 /*設(shè)置字符設(shè)備cdev結(jié)構(gòu)體*/
76 static void light_setup_cdev(struct light_dev *dev, int index)
77 {
78 int err, devno = MKDEV(light_major, index);
79 cdev_init(&dev->cdev, &light_fops);
80 dev->cdev.owner = THIS_MODULE;
81 dev->cdev.ops = &light_fops;
82 err = cdev_add(&dev->cdev, devno, 1);
83 if (err)
84 printk(KERN_NOTICE "Error %d adding LED%d", err, index);
85 }
86 /*模塊加載函數(shù)*/
87 int light_init(void)
88 {
89 int result;
90 dev_t dev = MKDEV(light_major, 0);
91 /* 申請字符設(shè)備號*/
92 if (light_major)
93 result = register_chrdev_region(dev, 1, "LED");
94 else {
95 result = alloc_chrdev_region(&dev, 0, 1, "LED");
96 light_major = MAJOR(dev);
97 }
98 if (result < 0)
99 return result;
100 /* 分配設(shè)備結(jié)構(gòu)體的內(nèi)存 */
101 light_devp = kmalloc(sizeof(struct light_dev), GFP_KERNEL);
102 if (!light_devp) {
103 result = -ENOMEM;
104 goto fail_malloc;
105 }
106 memset(light_devp, 0, sizeof(struct light_dev));
107 light_setup_cdev(light_devp, 0);
108 light_gpio_init();
109 return 0;
110 fail_malloc:
111 unregister_chrdev_region(dev, light_devp);
112 return result;
113 }
114 /*模塊卸載函數(shù)*/
115 void light_cleanup(void)
116 {
117 cdev_del(&light_devp->cdev); /*刪除字符設(shè)備結(jié)構(gòu)體*/
118 kfree(light_devp); /*釋放在light_init中分配的內(nèi)存*/
119 unregister_chrdev_region(MKDEV(light_major, 0), 1); /*刪除字符設(shè)備*/
120 }
121 module_init(light_init);
122 module_exit(light_cleanup);
熱點鏈接：
1、嵌入式linux驅(qū)動要學(xué)哪些
2、典型嵌入式Linux系統(tǒng)設(shè)置
更多新聞>> |
