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：

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：

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。