libusb_submit_transfer例子

下面是一个示例，展示如何使用libusb_submit_transfer函数提交传输：

#include <stdio.h>
#include <stdlib.h>
#include <libusb.h>

#define VENDOR_ID 0x0a5c
#define PRODUCT_ID 0x4503

#define ENDPOINT_IN 0x81
#define ENDPOINT_OUT 0x02

#define TRANSFER_SIZE 16

int main(void)
{
    libusb_device_handle *dev_handle;
    libusb_context *ctx = NULL;
    int r;

    // 初始化
    r = libusb_init(&ctx);
    if (r < 0)
    {
        fprintf(stderr, "libusb_init error: %d\n", r);
        return EXIT_FAILURE;
    }

    // 打开设备
    dev_handle = libusb_open_device_with_vid_pid(ctx, VENDOR_ID, PRODUCT_ID);
    if (dev_handle == NULL)
    {
        fprintf(stderr, "libusb_open_device_with_vid_pid error\n");
        libusb_exit(ctx);
        return EXIT_FAILURE;
    }

    // 分配传输缓冲区
    unsigned char *buffer = (unsigned char *)malloc(TRANSFER_SIZE);
    if (buffer == NULL)
    {
        fprintf(stderr, "malloc error\n");
        libusb_close(dev_handle);
        libusb_exit(ctx);
        return EXIT_FAILURE;
    }

    // 准备传输
    libusb_transfer *transfer = libusb_alloc_transfer(0);
    if (transfer == NULL)
    {
        fprintf(stderr, "libusb_alloc_transfer error\n");
        free(buffer);
        libusb_close(dev_handle);
        libusb_exit(ctx);
        return EXIT_FAILURE;
    }

    libusb_fill_bulk_transfer(transfer, dev_handle, ENDPOINT_OUT, buffer, TRANSFER_SIZE, NULL, NULL, 0);

    // 提交传输
    r = libusb_submit_transfer(transfer);
    if (r < 0)
    {
        fprintf(stderr, "libusb_submit_transfer error: %d\n", r);
        libusb_free_transfer(transfer);
        free(buffer);
        libusb_close(dev_handle);
        libusb_exit(ctx);
        return EXIT_FAILURE;
    }

    // 等待传输完成
    r = libusb_handle_events(ctx);
    if (r < 0)
    {
        fprintf(stderr, "libusb_handle_events error: %d\n", r);
        libusb_cancel_transfer(transfer);
        libusb_free_transfer(transfer);
        free(buffer);
        libusb_close(dev_handle);
        libusb_exit(ctx);
        return EXIT_FAILURE;
    }

    // 释放资源
    libusb_free_transfer(transfer);
    free(buffer);
    libusb_close(dev_handle);
    libusb_exit(ctx);
    return EXIT_SUCCESS;
}

这个示例使用libusb_open_device_with_vid_pid函数打开一个特定的USB设备，然后使用libusb_alloc_transfer函数分配一个传输结构体。

接下来，使用libusb_fill_bulk_transfer函数填充传输结构体，指定设备句柄、端点地址、缓冲区和缓冲区大小。然后，使用libusb_submit_transfer函数提交传输。

最后，使用libusb_handle_events函数等待传输完成。如果传输失败，可以使用libusb_cancel_transfer函数取消传输。