用libusb写一个usb通信例子

下面是一个利用libusb实现USB通信的例子，本例子实现的是使用USB-HID协议控制一个USB设备的LED灯开关：

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <libusb-1.0/libusb.h>

#define VENDOR_ID 0x1234
#define PRODUCT_ID 0x5678

#define HID_GET_REPORT 0x01
#define HID_SET_REPORT 0x09

#define REPORT_ID 0x01

static int send_report(libusb_device_handle *handle, const unsigned char *data, int length)
{
    int res, transferred;
    unsigned char buf[length + 1];
    memset(buf, 0, length + 1);
    buf[0] = REPORT_ID;
    memcpy(&buf[1], data, length);
    res = libusb_control_transfer(handle, LIBUSB_REQUEST_TYPE_CLASS | LIBUSB_ENDPOINT_OUT,
                                   HID_SET_REPORT, (REPORT_ID << 8) | 0x00, 0x00, buf, length + 1, 1000);
    if (res != length + 1) {
        fprintf(stderr, "Error: control transfer failed. %d\n", res);
        return -1;
    }
    res = libusb_interrupt_transfer(handle, 0x81, buf, length + 1, &transferred, 1000);
    if (res != 0) {
        fprintf(stderr, "Error: interrupt transfer failed. %d\n", res);
        return -1;
    }
    return 0;
}

int main(int argc, char **argv)
{
    libusb_device **devs;
    libusb_device_handle *handle;
    struct libusb_device_descriptor desc;
    int r, i, transferred;
    ssize_t cnt;
    unsigned char data[1];

    r = libusb_init(NULL);
    if (r < 0) {
        fprintf(stderr, "Error: failed to initialize libusb. %d\n", r);
        return -1;
    }

    cnt = libusb_get_device_list(NULL, &devs);
    if (cnt < 0) {
        fprintf(stderr, "Error: failed to get device list. %d\n", r);
        libusb_exit(NULL);
        return -1;
    }

    for (i = 0; i < cnt; i++) {
        r = libusb_get_device_descriptor(devs[i], &desc);
        if (r < 0) {
            fprintf(stderr, "Error: failed to get device descriptor. %d\n", r);
            break;
        }

        if (desc.idVendor == VENDOR_ID && desc.idProduct == PRODUCT_ID) {
            r = libusb_open(devs[i], &handle);
            if (r < 0) {
                fprintf(stderr, "Error: failed to open device. %d\n", r);
                break;
            }

            r = libusb_kernel_driver_active(handle, 0);
            if (r == 1) {
                r = libusb_detach_kernel_driver(handle, 0);
                if (r < 0) {
                    fprintf(stderr, "Error: failed to detach kernel driver. %d\n", r);
                    break;
                }
            }

            r = libusb_claim_interface(handle, 0);
            if (r < 0) {
                fprintf(stderr, "Error: failed to claim interface. %d\n", r);
                break;
            }

            data[0] = 0x01;
            send_report(handle, data, sizeof(data));

            data[0] = 0x00;
            send_report(handle, data, sizeof(data));

            libusb_release_interface(handle, 0);
            libusb_close(handle);
            break;
        }
    }

    libusb_free_device_list(devs, 1);
    libusb_exit(NULL);

    return 0;
}

这个例子打开一个VID为0x1234、PID为0x5678的USB设备，并控制设备的LED灯开关。具体实现过程是：先打开设备、卸载内核驱动和申请接口，然后发送一个开灯的命令和一个关灯的命令，最后释放接口和关闭设备。其中，`send_report`函数用于发送HID报告，通过控制传输和中断传输两个步骤实现。