USB子系统学习（四）用户态下使用libusb读取鼠标数据

1、声明

本文是在学习韦东山《驱动大全》USB子系统时，为梳理知识点和自己回看而记录，全部内容高度复制粘贴。

韦老师的《驱动大全》：商品详情

其对应的讲义资料：https://e.coding.net/weidongshan/linux/doc_and_source_for_drivers.git

libusb api：https://libusb.sourceforge.io/api-1.0/libusb_api.html

2、HID协议

HID：Human Interface Devices, 人类用来跟计算机交互的设备。就是鼠标、键盘、游戏手柄等设备。对于USB接口的HID设备，有一套协议。

2.1、描述符

HID设备有如下描述符：

• HID设备的"设备描述符"并无实际意义，没有使用"设备描述符"来表示自己是HID设备。
• HID设备只有一个配置，所以只有一个配置描述符。
• 接口描述符：
  • bInterfaceClass为3，表示它是HID设备。
  • bInterfaceSubClass是0或1，1表示它支持"Boot Interface"(表示PC的BIOS能识别、使用它)，0表示必须等操作系统启动后通过驱动程序来使用它。
  • bInterfaceProtocol：0-None, 1-键盘, 2-鼠标。
• 端点描述符：HID设备有一个控制端点、一个中断端点。

对于鼠标，HOST可以通过中断端点读到数据。

2.2、鼠标数据格式

通过中断传输可以读到鼠标数据，它是8字节的数据，格式如下：

偏移	大小	描述
0	1字节
1	1字节	按键状态
2	2字节	X位移
4	2字节	Y位移
6	1字节或2字节	滚轮

按键状态里，每一位对应鼠标的一个按键，等1时表示对应按键被点击了，格式如下：

位	长度	描述
0	1	鼠标的左键
1	1	鼠标的右键
2	1	鼠标的中间键
3	5	保留，设备自己定义bit3: 鼠标的侧边按键bit4:

X位移、Y位移都是8位的有符号数。对于X位移，负数表示鼠标向左移动，正数表示鼠标向右移动，移动的幅度就使用这个8位数据表示。对于Y位移，负数表示鼠标向上移动，正数表示鼠标向下移动，移动的幅度就使用这个8位数据表示。

3、应用程序

本次应用程序使用的是同步接口读取鼠标数据。

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <libusb-1.0/libusb.h>int main(int argc, char **argv)
{int err;libusb_device *dev, **devs;int num_devices;int endpoint;int interface_num;int transferred;int count = 0;unsigned char buffer[8];struct libusb_config_descriptor *config_desc;struct libusb_device_handle *dev_handle = NULL;int found = 0;/* libusb init */err = libusb_init(NULL);if (err < 0) {fprintf(stderr, "failed to initialise libusb %d - %s\n", err, libusb_strerror(err));exit(1);}/* get device list */if ((num_devices = libusb_get_device_list(NULL, &devs)) < 0)    // 获取设备描述符列表（函数返回设备描述符数量）{fprintf(stderr, "libusb_get_device_list() failed\n");libusb_exit(NULL);exit(1);}   fprintf(stdout, "libusb_get_device_list() ok\n");/* for each device, get config descriptor */for (int i = 0; i < num_devices; i++){dev = devs[i];err = libusb_get_config_descriptor(dev, 0, &config_desc);   // 获取配置描述符if (err) {fprintf(stderr, "could not get configuration descriptor\n");continue;}fprintf(stdout, "libusb_get_config_descriptor() ok\n");/* parse interface descriptor, find usb mouse */for (int interface = 0; interface < config_desc->bNumInterfaces; interface++)   // 枚举所有接口描述符{const struct libusb_interface_descriptor *intf_desc = &config_desc->interface[interface].altsetting[0];     // 获取配置描述符里的第一个接口描述符interface_num = intf_desc->bInterfaceNumber;        // 记录该接口描述符的编号（编号是从0开始）if (intf_desc->bInterfaceClass != 3 || intf_desc->bInterfaceProtocol != 2)  // 判断是否是HID设备和是否是鼠标协议continue;/* 找到了USB鼠标 */fprintf(stdout, "find usb mouse ok\n");for (int ep = 0; ep < intf_desc->bNumEndpoints; ep++)   // 枚举所有端点描述符{// 判断是否是中断传输，是否是输入端点（输入输出都是以USB Host来讨论，所以该端点是USB Device输出到USB Host）if ((intf_desc->endpoint[ep].bmAttributes & 3) == LIBUSB_TRANSFER_TYPE_INTERRUPT || (intf_desc->endpoint[ep].bEndpointAddress & 0x80) == LIBUSB_ENDPOINT_IN){/* 找到了输入的中断端点 */fprintf(stdout, "find in int endpoint\n");endpoint = intf_desc->endpoint[ep].bEndpointAddress;found = 1;break;}}if (found)break;}libusb_free_config_descriptor(config_desc);if (found)break; }if (!found){/* free device list */libusb_free_device_list(devs, 1);libusb_exit(NULL);exit(1);}/* libusb open */if (found){err = libusb_open(dev, &dev_handle);if (err){fprintf(stderr, "failed to open usb mouse\n");exit(1);}fprintf(stdout, "libusb_open ok\n");}/* free device list */libusb_free_device_list(devs, 1);/* claim interface */libusb_set_auto_detach_kernel_driver(dev_handle, 1);  err = libusb_claim_interface(dev_handle, interface_num);if (err){fprintf(stderr, "failed to libusb_claim_interface\n");exit(1);}fprintf(stdout, "libusb_claim_interface ok\n");/* libusb interrupt transfer */while (1){err = libusb_interrupt_transfer(dev_handle, endpoint, buffer, 8, &transferred, 5000);		// 发起中断传输，阻塞等待，5s超时时间if (!err) {/* parser data */printf("%04d datas: ", count++);printf("recv datas len = %d\n", transferred);for (int i = 0; i < transferred; i++){printf("%02x ", buffer[i]);}printf("\n");} else if (err == LIBUSB_ERROR_TIMEOUT){fprintf(stderr, "libusb_interrupt_transfer timout\n");} else {const char *errname = libusb_error_name(err);fprintf(stderr, "libusb_interrupt_transfer err : %d, %s\n", err, errname);//exit(1);}}/* libusb close */libusb_release_interface(dev_handle, interface_num);libusb_close(dev_handle);libusb_exit(NULL);
}

4、编译应用程序

假设你的开发板是ubuntu系统：

# 安装libusb库
$ sudo apt install libusb-1.0-0-dev# 编译程序
$ gcc -o readmouse readmouse.c -lusb-1.0

5、测试

将usb鼠标插入开发板：

执行程序：

$ sudo ./readmouse

移动鼠标：

滚轮滑动：

按键状态：

另外，每个鼠标的数据格式是不一样的。以上测试结果只是我使用的鼠标。

6、其它

以下是使用异步接口读取鼠标数据的测试程序。

#include <errno.h>
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>#include <libusb-1.0/libusb.h>struct usb_mouse {struct libusb_device_handle *handle;int interface;int endpoint;unsigned char buf[16];int transferred;struct libusb_transfer *transfer;struct usb_mouse *next;
};static struct usb_mouse *usb_mouse_list;void free_usb_mouses(struct usb_mouse *usb_mouse_list)
{struct usb_mouse *pnext;while (usb_mouse_list){pnext = usb_mouse_list->next;free(usb_mouse_list);usb_mouse_list = pnext;}
}int get_usb_mouse(libusb_device **devs, int num_devices, struct usb_mouse **usb_mouse_list)
{int err;libusb_device *dev;int endpoint;int interface_num;struct libusb_config_descriptor *config_desc;struct libusb_device_handle *dev_handle = NULL;struct usb_mouse *pmouse;struct usb_mouse *list = NULL;int mouse_cnt = 0;/* for each device, get config descriptor */for (int i = 0; i < num_devices; i++) {dev = devs[i];/* parse interface descriptor, find usb mouse */        err = libusb_get_config_descriptor(dev, 0, &config_desc);       // 获取配置描述符if (err) {fprintf(stderr, "could not get configuration descriptor\n");continue;}fprintf(stdout, "libusb_get_config_descriptor() ok\n");for (int interface = 0; interface < config_desc->bNumInterfaces; interface++) {     // 枚举所有接口描述符const struct libusb_interface_descriptor *intf_desc = &config_desc->interface[interface].altsetting[0];interface_num = intf_desc->bInterfaceNumber;        // 记录该接口描述符的编号（编号是从0开始）if (intf_desc->bInterfaceClass != 3 || intf_desc->bInterfaceProtocol != 2)      // 判断是否是HID设备和是否是鼠标协议    continue;else{/* 找到了USB鼠标 */fprintf(stdout, "find usb mouse ok\n");for (int ep = 0; ep < intf_desc->bNumEndpoints; ep++)   // 枚举所有端点描述符{// 判断是否是中断传输，是否是输入端点（输入输出都是以USB Host来讨论，所以该端点是USB Device输出到USB Host）if ((intf_desc->endpoint[ep].bmAttributes & 3) == LIBUSB_TRANSFER_TYPE_INTERRUPT ||(intf_desc->endpoint[ep].bEndpointAddress & 0x80) == LIBUSB_ENDPOINT_IN) {/* 找到了输入的中断端点 */fprintf(stdout, "find in int endpoint\n");endpoint = intf_desc->endpoint[ep].bEndpointAddress;/* libusb_open */err = libusb_open(dev, &dev_handle);if (err){fprintf(stderr, "failed to open usb mouse\n");return -1;}fprintf(stdout, "libusb_open ok\n");/* 记录下来: 放入链表 */pmouse = malloc(sizeof(struct usb_mouse));if (!pmouse){fprintf(stderr, "can not malloc\n");return -1;}pmouse->endpoint  = endpoint;pmouse->interface = interface_num;pmouse->handle    = dev_handle;pmouse->next      = NULL;if (!list)list = pmouse;else{pmouse->next = list;list = pmouse;}mouse_cnt++;break;}}}}libusb_free_config_descriptor(config_desc);}*usb_mouse_list = list;return mouse_cnt;
}static void mouse_irq(struct libusb_transfer *transfer)
{static int count = 0;if (transfer->status == LIBUSB_TRANSFER_COMPLETED){/* parser data */printf("%04d datas: ", count++);for (int i = 0; i < transfer->actual_length; i++){printf("%02x ", transfer->buffer[i]);}printf("\n");}if (libusb_submit_transfer(transfer) < 0){fprintf(stderr, "libusb_submit_transfer err\n");}
}int main(int argc, char **argv)
{int err;libusb_device **devs;int num_devices, num_mouse;struct usb_mouse *pmouse;/* libusb init */err = libusb_init(NULL);if (err < 0) {fprintf(stderr, "failed to initialise libusb %d - %s\n", err, libusb_strerror(err));exit(1);}/* get device list */if ((num_devices = libusb_get_device_list(NULL, &devs)) < 0)    // 获取设备描述符列表（函数返回设备描述符数量）{fprintf(stderr, "libusb_get_device_list() failed\n");libusb_exit(NULL);exit(1);}   fprintf(stdout, "libusb_get_device_list() ok\n");/* get usb mouse */num_mouse = get_usb_mouse(devs, num_devices, &usb_mouse_list);if (num_mouse <= 0){/* free device list */libusb_free_device_list(devs, 1);libusb_exit(NULL);exit(1);}fprintf(stdout, "get %d mouses\n", num_mouse);/* free device list */libusb_free_device_list(devs, 1);/* claim interface */pmouse = usb_mouse_list;while (pmouse){libusb_set_auto_detach_kernel_driver(pmouse->handle, 1);  err = libusb_claim_interface(pmouse->handle, pmouse->interface);if (err){fprintf(stderr, "failed to libusb_claim_interface\n");exit(1);}pmouse = pmouse->next;}fprintf(stdout, "libusb_claim_interface ok\n");/* for each mouse, alloc transfer, fill transfer, submit transfer */pmouse = usb_mouse_list;while (pmouse){/* alloc transfer */pmouse->transfer = libusb_alloc_transfer(0);/* fill transfer */libusb_fill_interrupt_transfer(pmouse->transfer, pmouse->handle, pmouse->endpoint, pmouse->buf,sizeof(pmouse->buf), mouse_irq, pmouse, 0);/* submit transfer */libusb_submit_transfer(pmouse->transfer);pmouse = pmouse->next;}/* handle events */while (1) {struct timeval tv = { 5, 0 };int r;r = libusb_handle_events_timeout(NULL, &tv);if (r < 0) {fprintf(stderr, "libusb_handle_events_timeout err\n");break;}}/* libusb_close */pmouse = usb_mouse_list;while (pmouse){libusb_release_interface(pmouse->handle, pmouse->interface);libusb_close(pmouse->handle);        pmouse = pmouse->next;}free_usb_mouses(usb_mouse_list);libusb_exit(NULL);}

运行程序前，先把多个鼠标插入开发板，然后运行测试程序，移动鼠标，查看打印结果。