嵌入式Linux驱动笔记(四)------USB键盘驱动程序

你好！这里是风筝的博客，

欢迎和我一起交流。

Kernel版本为4.4.17.

编写USB键盘的驱动，可以参考Kernel里的usbkbd.c这个文件.

我越发觉得驱动都是按套路来的.......流程都差不多一样.

在这个文件里，最主要就是看usb_kbd_probe函数和usb_kbd_irq函数了。

在文件最开头有个数组：

static const unsigned char usb_kbd_keycode[256] = {  0,  0,  0,  0, 30, 48, 46, 32, 18, 33, 34, 35, 23, 36, 37, 38, 50, 49, 24, 25, 16, 19, 31, 20, 22, 47, 17, 45, 21, 44,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 28,  1, 14, 15, 57, 12, 13, 26, 27, 43, 43, 39, 40, 41, 51, 52, 53, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 87, 88, 99, 70,119,110,102,104,111,107,109,106,105,108,103, 69, 98, 55, 74, 78, 96, 79, 80, 81, 75, 76, 77, 71, 72, 73, 82, 83, 86,127,116,117,183,184,185,186,187,188,189,190,191,192,193,194,134,138,130,132,128,129,131,137,133,135,136,113,115,114,  0,  0,  0,121,  0, 89, 93,124, 92, 94, 95,  0,  0,  0,122,123, 90, 91, 85,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 29, 42, 56,125, 97, 54,100,126,164,166,165,163,161,115,114,113,150,158,159,128,136,177,178,176,142,152,173,140};

这个是USB键盘的码表，上报按键事件的时候需要用到。
接下来就是usb_kbd_probe函数了，就一点点内容，我都用注释写好了，还是比较简单的（其实注释也是我抄来的，///////捂脸）

static int usb_kbd_probe(struct usb_interface *iface, const struct usb_device_id *id){struct usb_device *dev = interface_to_usbdev(iface);struct usb_host_interface *interface;struct usb_endpoint_descriptor *endpoint;struct usb_kbd *kbd;struct input_dev *input_dev;int i, pipe, maxp;int error = -ENOMEM;interface = iface->cur_altsetting;if (interface->desc.bNumEndpoints != 1)return -ENODEV;endpoint = &interface->endpoint[0].desc;if (!usb_endpoint_is_int_in(endpoint))return -ENODEV;pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);maxp = usb_maxpacket(dev, pipe, usb_pipeout(pipe));kbd = kzalloc(sizeof(struct usb_kbd), GFP_KERNEL);input_dev = input_allocate_device();if (!kbd || !input_dev)goto fail1;if (usb_kbd_alloc_mem(dev, kbd))goto fail2;/* 填充 usb 设备结构体和输入设备结构体 */kbd->usbdev = dev;kbd->dev = input_dev;spin_lock_init(&kbd->leds_lock);/*以"厂商名字 产品名字"的格式将其写入kbd->name*/if (dev->manufacturer)strlcpy(kbd->name, dev->manufacturer, sizeof(kbd->name));if (dev->product) {if (dev->manufacturer)strlcat(kbd->name, " ", sizeof(kbd->name));strlcat(kbd->name, dev->product, sizeof(kbd->name));}/*检测不到厂商名字*/if (!strlen(kbd->name))snprintf(kbd->name, sizeof(kbd->name), "USB HIDBP Keyboard %04x:%04x", le16_to_cpu(dev->descriptor.idVendor), le16_to_cpu(dev->descriptor.idProduct));/*设备链接地址*/usb_make_path(dev, kbd->phys, sizeof(kbd->phys));strlcat(kbd->phys, "/input0", sizeof(kbd->phys));input_dev->name = kbd->name;input_dev->phys = kbd->phys;usb_to_input_id(dev, &input_dev->id);input_dev->dev.parent = &iface->dev;input_set_drvdata(input_dev, kbd);input_dev->evbit[0] = BIT_MASK(EV_KEY) | BIT_MASK(EV_LED) |BIT_MASK(EV_REP);input_dev->ledbit[0] = BIT_MASK(LED_NUML) | BIT_MASK(LED_CAPSL) |BIT_MASK(LED_SCROLLL) | BIT_MASK(LED_COMPOSE) |BIT_MASK(LED_KANA);for (i = 0; i < 255; i++)set_bit(usb_kbd_keycode[i], input_dev->keybit);clear_bit(0, input_dev->keybit);input_dev->event = usb_kbd_event;input_dev->open = usb_kbd_open;input_dev->close = usb_kbd_close;/*初始化中断URB*/usb_fill_int_urb(kbd->irq, dev, pipe, kbd->new, (maxp > 8 ? 8 : maxp), usb_kbd_irq, kbd, endpoint->bInterval);kbd->irq->transfer_dma = kbd->new_dma;kbd->irq->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;kbd->cr->bRequestType = USB_TYPE_CLASS | USB_RECIP_INTERFACE;kbd->cr->bRequest = 0x09;kbd->cr->wValue = cpu_to_le16(0x200);kbd->cr->wIndex = cpu_to_le16(interface->desc.bInterfaceNumber);kbd->cr->wLength = cpu_to_le16(1);/*初始化控制URB*/usb_fill_control_urb(kbd->led, dev, usb_sndctrlpipe(dev, 0),     (void *) kbd->cr, kbd->leds, 1,     usb_kbd_led, kbd);kbd->led->transfer_dma = kbd->leds_dma;kbd->led->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;error = input_register_device(kbd->dev);if (error)goto fail2;usb_set_intfdata(iface, kbd);device_set_wakeup_enable(&dev->dev, 1);return 0;fail2:usb_kbd_free_mem(dev, kbd);fail1:input_free_device(input_dev);kfree(kbd);return error;}

感觉主要的也没什么，就是：

选择interface.

获取描述符.

将endpoint设置为中断IN端点.

分配kbd、input_dev空间.

填充 usb 设备结构体和输入设备结构体 .

以"厂商名字 产品名字"的格式将其写入kbd->name.

设置上报输入子系统的事件类型.

设置上报输入子系统的事件有什么.

设置注册事件的处理、打开、关闭函数入口.

初始化中断URB.

初始化控制URB.

感觉就差不多了。

主要的还是usb_kbd_irq中断函数。

static void usb_kbd_irq(struct urb *urb){struct usb_kbd *kbd = urb->context;int i;switch (urb->status) {case 0:/* success */break;case -ECONNRESET:/* unlink */case -ENOENT:case -ESHUTDOWN:return;/* -EPIPE:  should clear the halt */default:/* error */goto resubmit;}for (i = 0; i < 8; i++)input_report_key(kbd->dev, usb_kbd_keycode[i + 224], (kbd->new[0] >> i) & 1);for (i = 2; i < 8; i++) {if (kbd->old[i] > 3 && memscan(kbd->new + 2, kbd->old[i], 6) == kbd->new + 8) {if (usb_kbd_keycode[kbd->old[i]])input_report_key(kbd->dev, usb_kbd_keycode[kbd->old[i]], 0);elsehid_info(urb->dev, "Unknown key (scancode %#x) released.\n", kbd->old[i]);}if (kbd->new[i] > 3 && memscan(kbd->old + 2, kbd->new[i], 6) == kbd->old + 8) {if (usb_kbd_keycode[kbd->new[i]])input_report_key(kbd->dev, usb_kbd_keycode[kbd->new[i]], 1);elsehid_info(urb->dev, "Unknown key (scancode %#x) pressed.\n", kbd->new[i]);}}input_sync(kbd->dev);memcpy(kbd->old, kbd->new, 8);resubmit:i = usb_submit_urb (urb, GFP_ATOMIC);/*发送USB请求块*/if (i)hid_err(urb->dev, "can't resubmit intr, %s-%s/input0, status %d",kbd->usbdev->bus->bus_name,kbd->usbdev->devpath, i);} 

其中，每次中断接收的值都是8个字节，是这样的：

data0 data1 data2 data3 data4 data5 data6 data7 

一般，只按下一个键时，键值会出现在data2上。

如按下键盘a时，数据为：00 00 04 00 00 00 00 00.

a键松开时，数据为：00 00 00 00 00 00 00 00.

同时按下两个键时，第二个键的键值会出现在data3上。

如按下a时再按下b键，数据为：00 00 04 05 00 00 00 00.

所以能同时按下6个按键。

接下来就很好分析中断函数了：

for (i = 0; i < 8; i++)input_report_key(kbd->dev, usb_kbd_keycode[i + 224], (kbd->new[0] >> i) & 1);

这一句是用来检测修饰按键的，虽然我也不造修饰按键是什么......

其中，kbd->new为urb的缓冲区，在probe函数里有一句：usb_kbd_alloc_mem(dev, kbd)，函数中为kbd->new分配8字节内存：kbd->new = usb_buffer_alloc(dev, 8, GFP_ATOMIC, &kbd->new_dma), 
并且在中断urb初始化函数中usb_fill_int_urb(kbd->irq, dev, pipe, kbd->new, (maxp > 8 ? 8 : maxp), usb_kbd_irq, kbd, endpoint->bInterval); 
即从端点里取得的数据会放在new指向的内存里面，最大为8字节.
接下来的才是真正的常用按键检测：

for (i = 2; i < 8; i++) {if (kbd->old[i] > 3 && memscan(kbd->new + 2, kbd->old[i], 6) == kbd->new + 8) {if (usb_kbd_keycode[kbd->old[i]])input_report_key(kbd->dev, usb_kbd_keycode[kbd->old[i]], 0);elsehid_info(urb->dev, "Unknown key (scancode %#x) released.\n", kbd->old[i]);}if (kbd->new[i] > 3 && memscan(kbd->old + 2, kbd->new[i], 6) == kbd->old + 8) {if (usb_kbd_keycode[kbd->new[i]])input_report_key(kbd->dev, usb_kbd_keycode[kbd->new[i]], 1);elsehid_info(urb->dev, "Unknown key (scancode %#x) pressed.\n", kbd->new[i]);}}

因为键值是在data2及其之后存放的，所以for循环从i=2开始查询。

for里面有两个if，第一个if是判断按键是否是松开的，第二个if是判断按键是否被按下的。

其中memscan函数是判断键值是否相等的，kbd->old存放的是上一次按键的数据，kbd->new是这一次按键的数据，memscan函数在string.c里，如下：

void *memscan(void *addr, int c, size_t size){unsigned char *p = addr;while (size) {if (*p == c)return (void *)p;p++;size--;}  return (void *)p;}

很简单的一个c语言函数，主要就是判断是否相等而已。通过上一次数据和这一次数据的比较就知道按键是否被按下了。然后上报按键事件即可。
最后，memcpy(kbd->old, kbd->new, 8);就是把kbd->new的成员赋值给kbd->old，实现新旧数据存储。

好了。接下来写驱动程序就照葫芦画瓢就可以了：

/*参考usbkbd.c*/#include <linux/kernel.h>#include <linux/slab.h>#include <linux/module.h>#include <linux/init.h>#include <linux/usb/input.h>#include <linux/hid.h>static const unsigned char usb_kbd_keycode[256] = {/*键值码表*/  0,  0,  0,  0, 30, 48, 46, 32, 18, 33, 34, 35, 23, 36, 37, 38, 50, 49, 24, 25, 16, 19, 31, 20, 22, 47, 17, 45, 21, 44,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 28,  1, 14, 15, 57, 12, 13, 26, 27, 43, 43, 39, 40, 41, 51, 52, 53, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 87, 88, 99, 70,119,110,102,104,111,107,109,106,105,108,103, 69, 98, 55, 74, 78, 96, 79, 80, 81, 75, 76, 77, 71, 72, 73, 82, 83, 86,127,116,117,183,184,185,186,187,188,189,190,191,192,193,194,134,138,130,132,128,129,131,137,133,135,136,113,115,114,  0,  0,  0,121,  0, 89, 93,124, 92, 94, 95,  0,  0,  0,122,123, 90, 91, 85,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0,  0, 29, 42, 56,125, 97, 54,100,126,164,166,165,163,161,115,114,113,150,158,159,128,136,177,178,176,142,152,173,140};static int len;static struct input_dev *uk_dev;static char *usb_buf;static dma_addr_t usb_buf_phys;static struct urb *uk_urb;static struct usb_device_id keyboard_id_table [] = {{ USB_INTERFACE_INFO(USB_INTERFACE_CLASS_HID, USB_INTERFACE_SUBCLASS_BOOT,USB_INTERFACE_PROTOCOL_KEYBOARD) },/*3,1,1分别表示接口类,接口子类,接口协议;3,1,1为键盘接口类;鼠标为3,1,2*/{ }/* Terminating entry */};void buffer_copy (char *usb_buf_source , char *usb_buf_target , int len){int i;for(i=0;i<len;i++){usb_buf_target[i] = usb_buf_source[i];}}static void keyboard_irq(struct urb *urb){struct usb_kbd *kbd = urb->context;int i;static char usb_buf_pre_val[8];for (i = 2; i < 8; i++) {/*若同时只按下1个按键则在第[2]个字节,若同时有两个按键则第二个在第[3]字节，类推最多可有6个按键同时按下*/ if(usb_buf[i]!=usb_buf_pre_val[i]){if((usb_buf[i] ) ? 1 : 0)input_report_key(uk_dev, usb_kbd_keycode[usb_buf[i]],  1);elseinput_report_key(uk_dev, usb_kbd_keycode[usb_buf_pre_val[i]],  0);}}/*同步设备,告知事件的接收者驱动已经发出了一个完整的报告*/ input_sync(uk_dev);buffer_copy(usb_buf , usb_buf_pre_val , 8);/*防止未松开时被当成新的按键处理*//* 重新提交urb */usb_submit_urb(uk_urb, GFP_KERNEL);}static int keyboard_probe(struct usb_interface *intf, const struct usb_device_id *id){struct usb_device *dev = interface_to_usbdev(intf);struct usb_host_interface *interface;struct usb_endpoint_descriptor *endpoint;int pipe;/*当前选择的interface*/interface = intf->cur_altsetting;/*获取端点描述符*/endpoint = &interface->endpoint[0].desc;/* a. 分配一个input_dev */uk_dev = input_allocate_device();    if ( !uk_dev)printk("allocate false \n");/* b. 设置 *//* b.1 能产生哪类事件 */set_bit(EV_KEY, uk_dev->evbit);/*键码事件*/set_bit(EV_REP, uk_dev->evbit);/*自动重覆数值*/;uk_dev->ledbit[0] = BIT(LED_NUML)/*数字灯*/ | BIT(LED_CAPSL)/*大小写灯*/ | BIT(LED_SCROLLL)/*滚动灯*/ | BIT(LED_COMPOSE) | BIT(LED_KANA);/* b.2 能产生哪些事件 */for (len = 0; len < 255; len++) set_bit(usb_kbd_keycode[len], uk_dev->keybit);clear_bit(0, uk_dev->keybit);/* c. 注册 */input_register_device(uk_dev);/* d. 硬件相关操作 *//* 数据传输3要素: 源,目的,长度 *//* 源: USB设备的某个端点 */pipe = usb_rcvintpipe(dev, endpoint->bEndpointAddress);/*将endpoint设置为中断IN端点*//* 长度: */len = endpoint->wMaxPacketSize;/* 目的: *///usb_buf = usb_buffer_alloc(dev, len, GFP_ATOMIC, &usb_buf_phys);usb_buf = usb_alloc_coherent(dev, len, GFP_ATOMIC, &usb_buf_phys);/* 使用"3要素" *//* 分配usb request block */uk_urb = usb_alloc_urb(0, GFP_KERNEL);/* 使用"3要素设置urb" */usb_fill_int_urb(uk_urb, dev, pipe, usb_buf, len, keyboard_irq, NULL, endpoint->bInterval);uk_urb->transfer_dma = usb_buf_phys;uk_urb->transfer_flags |= URB_NO_TRANSFER_DMA_MAP;/* 使用URB */usb_submit_urb(uk_urb, GFP_KERNEL);/*发送USB请求块*/return 0;}static void keyboard_disconnect(struct usb_interface *intf){struct usb_device *dev = interface_to_usbdev(intf);usb_kill_urb(uk_urb);usb_free_urb(uk_urb);usb_free_coherent(dev, len, usb_buf, usb_buf_phys);input_unregister_device(uk_dev);input_free_device(uk_dev);}/* 1. 分配/设置usb_driver */static struct usb_driver keyboard_driver = {/*任何一个LINUX下的驱动都有个类似的驱动结构*/.name= "my_keyboard",.probe= keyboard_probe,/*驱动探测函数,加载时用到*/.disconnect= keyboard_disconnect,.id_table= keyboard_id_table,/*驱动设备ID表,用来指定设备或接口*/ };static int keyboard_init(void){/* 2. 注册 */int result = usb_register(&keyboard_driver);if (result != 0) /*注册失败*/ printk("register false \n");return 0;}static void keyboard_exit(void){usb_deregister(&keyboard_driver);}module_init(keyboard_init);module_exit(keyboard_exit);MODULE_LICENSE("GPL");

其中kbd我没有用到，就不写了，实现了按键即可。

Makefile:

KERN_DIR = /work/system/linux-4.4.17all:make -C $(KERN_DIR) M=`pwd` modules clean:make -C $(KERN_DIR) M=`pwd` modules cleanrm -rf modules.orderobj-m+= my_keyboard.o

最后make编译好，insmod my_keyboard.ko

插上键盘即可，usb键盘是热拔插的，随便插都没事。

cat /dev/tty1

即可看到在键盘按下的数据。

哦，忘记了，我是4.4.17的Kernel，usb键盘的驱动是没被编译进内核的，所以insmod自己写的驱动时不会出问题，其他的Kernel需要自己注意下，避免加载冲突了。

要是想用Kernel自带的驱动，在

Device Drivers  ---> HID support  ---> USB HID support  ---> < > USB HID transport layer

选中<*> USB HID transport layer即可。

估计以前的Kernel是

Device Drivers  ---> HID support  ---><*>  USB Human Interface Device (full HID) suppoort

默认是选中的，反正我现在的Kernel是 USB Human Interface Device (full HID) suppoort没有了的，估计就是变成了USB HID transport layer