libusb_bulk_transfer 说明

libusb_bulk_transfer函数说明

1.  
   API_EXPORTED int libusb_bulk_transfer(struct libusb_device_handle *dev_handle,
2.  
   unsigned char endpoint, unsigned char *data, int length, int *transferred,
3.  
   unsigned int timeout)
4.  
   {
5.  
   // 调用do_sync_bulk_transfer
6.  
   return do_sync_bulk_transfer(dev_handle, endpoint, data, length,
7.  
   transferred, timeout, LIBUSB_TRANSFER_TYPE_BULK);
8.  
   }

代码：

1.  
   static int do_sync_bulk_transfer(struct libusb_device_handle *dev_handle,
2.  
   unsigned char endpoint, unsigned char *buffer, int length,
3.  
   int *transferred, unsigned int timeout, unsigned char type)
4.  
   {
5.  
   struct libusb_transfer *transfer = libusb_alloc_transfer(0);
6.  
   int completed = 0;
7.  
   int r;
8.  
    
9.  
   if (!transfer)
10.  
    return LIBUSB_ERROR_NO_MEM;
11.  
     
12.  
    //传输结构 想必其核心就是传输的数据以及一些状态 其实就是货车
13.  
    libusb_fill_bulk_transfer(transfer, dev_handle, endpoint, buffer, length,
14.  
    bulk_transfer_cb, &completed, timeout);
15.  
    transfer->type = type;
16.  
     
17.  
    //在货车装完货物就可以出发了， 申请传输
18.  
    r = libusb_submit_transfer(transfer);
19.  
    if (r < 0) {
20.  
    libusb_free_transfer(transfer);
21.  
    return r;
22.  
    }
23.  
     
24.  
     
25.  
     
26.  
    //complete就是一个装载完毕的标准
27.  
     
28.  
    while (!completed) {
29.  
    r = libusb_handle_events(HANDLE_CTX(dev_handle));
30.  
    if (r < 0) {
31.  
    if (r == LIBUSB_ERROR_INTERRUPTED)
32.  
    continue;
33.  
    libusb_cancel_transfer(transfer);
34.  
    while (!completed)
35.  
    if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
36.  
    break;
37.  
    libusb_free_transfer(transfer);
38.  
    return r;
39.  
    }
40.  
    }
41.  
     
42.  
    *transferred = transfer->actual_length;
43.  
    switch (transfer->status) {
44.  
    case LIBUSB_TRANSFER_COMPLETED:
45.  
    r = 0;
46.  
    break;
47.  
    case LIBUSB_TRANSFER_TIMED_OUT:
48.  
    r = LIBUSB_ERROR_TIMEOUT;
49.  
    break;
50.  
    case LIBUSB_TRANSFER_STALL:
51.  
    r = LIBUSB_ERROR_PIPE;
52.  
    break;
53.  
    case LIBUSB_TRANSFER_OVERFLOW:
54.  
    r = LIBUSB_ERROR_OVERFLOW;
55.  
    break;
56.  
    case LIBUSB_TRANSFER_NO_DEVICE:
57.  
    r = LIBUSB_ERROR_NO_DEVICE;
58.  
    break;
59.  
    default:
60.  
    usbi_warn(HANDLE_CTX(dev_handle),
61.  
    "unrecognised status code %d", transfer->status);
62.  
    r = LIBUSB_ERROR_OTHER;
63.  
    }
64.  
    libusb_free_transfer(transfer);
65.  
    return r;
66.  
    }

     

    https://blog.csdn.net/zdyueguanyun/article/details/51192885