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; 在(zai)嵌(qian)入式系統的(de)設計中，LED一(yi)般(ban)(ban)直(zhi)接由(you)(you)CPU的(de)GPIO（通(tong)用可(ke)(ke)編程I/O口）控(kong)(kong)制。GPIO一(yi)般(ban)(ban)由(you)(you)兩組(zu)寄(ji)存器控(kong)(kong)制，即一(yi)組(zu)控(kong)(kong)制寄(ji)存器和一(yi)組(zu)數(shu)據(ju)寄(ji)存器。控(kong)(kong)制寄(ji)存器可(ke)(ke)設置GPIO口的(de)工作方式為輸(shu)入或是輸(shu)出。當引(yin)(yin)腳被設置為輸(shu)出時(shi)，向數(shu)據(ju)寄(ji)存器的(de)對(dui)應位(wei)寫入1和0會分別在(zai)引(yin)(yin)腳上產生(sheng)高電(dian)平和低電(dian)平；當引(yin)(yin)腳設置為輸(shu)入時(shi)，讀取數(shu)據(ju)寄(ji)存器的(de)對(dui)應位(wei)可(ke)(ke)獲得引(yin)(yin)腳上的(de)電(dian)平為高或低。
LED設備(bei)介于字符設備(bei)和塊設備(bei)之(zhi)間(jian)我們稱之(zhi)為misc（雜設備(bei)），其實按(an)linux下(xia)的(de)驅動位置來(lai)講還是一(yi)種字符設備(bei)。代碼清單1.1給(gei)出了Linux下(xia)LED的(de)驅動。
代碼清單1.1 Linux操作系統(tong)下LED的驅動(dong)
1 #include .../*包含內核中的多個頭文件*/
2 /*設備結構體*/
3 struct light_dev {
4 struct cdev cdev; /*字符設備cdev結構體*/
5 unsigned char vaule; /*LED亮時為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 /*打開和關閉函數*/
12 int light_open(struct inode *inode, struct file *filp)
13 {
14 struct light_dev *dev;
15 /* 獲得設備結構體指針 */
16 dev = container_of(inode->i_cdev, struct light_dev, cdev);
17 /* 讓設備結構體作為設備的私有信息 */
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; /*獲得設備結構體 */
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 */
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 /*設置字符設備cdev結構體*/
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*/
87 int light_init(void)
88 {
89 int result;
90 dev_t dev = MKDEV(light_major, 0);
91 /* 申請字符設備號*/
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 /* 分配設備結構體的內存 */
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*/
115 void light_cleanup(void)
116 {
117 cdev_del(&light_devp->cdev); /*刪除字符設備結構體*/
118 kfree(light_devp); /*釋放在light_init中分配的內存*/
119 unregister_chrdev_region(MKDEV(light_major, 0), 1); /*刪除字符設備*/
120 }
121 module_init(light_init);
122 module_exit(light_cleanup);
熱點(dian)鏈(lian)接：
1、嵌入式linux驅動要學哪些
2、典型嵌入式Linux系統設置
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