libusb_bulk_transfer函数说明
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API_EXPORTED int libusb_bulk_transfer(struct libusb_device_handle *dev_handle,
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unsigned char endpoint, unsigned char *data, int length, int *transferred,
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unsigned int timeout)
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{
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// 调用do_sync_bulk_transfer
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return do_sync_bulk_transfer(dev_handle, endpoint, data, length,
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transferred, timeout, LIBUSB_TRANSFER_TYPE_BULK);
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}
代码：
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static int do_sync_bulk_transfer(struct libusb_device_handle *dev_handle,
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unsigned char endpoint, unsigned char *buffer, int length,
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int *transferred, unsigned int timeout, unsigned char type)
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{
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struct libusb_transfer *transfer = libusb_alloc_transfer(0);
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int completed = 0;
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int r;
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if (!transfer)
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return LIBUSB_ERROR_NO_MEM;
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//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
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libusb_fill_bulk_transfer(transfer, dev_handle, endpoint, buffer, length,
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bulk_transfer_cb, &completed, timeout);
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transfer->type = type;
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//在货车装完货物就可以出发了， 申请传输
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r = libusb_submit_transfer(transfer);
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if (r < 0) {
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libusb_free_transfer(transfer);
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return r;
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}
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//complete就是一个装载完毕的标准
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while (!completed) {
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r = libusb_handle_events(HANDLE_CTX(dev_handle));
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if (r < 0) {
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if (r == LIBUSB_ERROR_INTERRUPTED)
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continue;
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libusb_cancel_transfer(transfer);
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while (!completed)
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if (libusb_handle_events(HANDLE_CTX(dev_handle)) < 0)
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break;
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libusb_free_transfer(transfer);
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return r;
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}
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}
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*transferred = transfer->actual_length;
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switch (transfer->status) {
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case LIBUSB_TRANSFER_COMPLETED:
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r = 0;
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break;
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case LIBUSB_TRANSFER_TIMED_OUT:
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r = LIBUSB_ERROR_TIMEOUT;
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break;
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case LIBUSB_TRANSFER_STALL:
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r = LIBUSB_ERROR_PIPE;
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break;
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case LIBUSB_TRANSFER_OVERFLOW:
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r = LIBUSB_ERROR_OVERFLOW;
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break;
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case LIBUSB_TRANSFER_NO_DEVICE:
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r = LIBUSB_ERROR_NO_DEVICE;
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break;
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default:
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usbi_warn(HANDLE_CTX(dev_handle),
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"unrecognised status code %d", transfer->status);
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r = LIBUSB_ERROR_OTHER;
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}
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libusb_free_transfer(transfer);
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return r;
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}https://blog.csdn.net/zdyueguanyun/article/details/51192885