libusb的控制传输（端点0）

int API_EXPORTED libusb_control_transfer(libusb_device_handle *dev_handle,
	uint8_t bmRequestType, uint8_t bRequest, uint16_t wValue, uint16_t wIndex,
	unsigned char *data, uint16_t wLength, unsigned int timeout)
{
	struct libusb_transfer *transfer = libusb_alloc_transfer(0);
	unsigned char *buffer;
	int completed = 0;
	int r;
 
	if (UNLIKELY(!transfer))
		return LIBUSB_ERROR_NO_MEM;
 
	buffer = (unsigned char*) malloc(LIBUSB_CONTROL_SETUP_SIZE + wLength);
	if (UNLIKELY(!buffer)) {
		libusb_free_transfer(transfer);
		return LIBUSB_ERROR_NO_MEM;
	}
 
	libusb_fill_control_setup(buffer, bmRequestType, bRequest, wValue, wIndex, wLength);
	if ((bmRequestType & LIBUSB_ENDPOINT_DIR_MASK) == LIBUSB_ENDPOINT_OUT)
		memcpy(buffer + LIBUSB_CONTROL_SETUP_SIZE, data, wLength);
 
	libusb_fill_control_transfer(transfer, dev_handle, buffer,
		sync_transfer_cb, &completed, timeout);
	transfer->flags = LIBUSB_TRANSFER_FREE_BUFFER;
	r = libusb_submit_transfer(transfer);
	if (UNLIKELY(r < 0)) {
		libusb_free_transfer(transfer);
		return r;
	}
 
	sync_transfer_wait_for_completion(transfer);
 
	if ((bmRequestType & LIBUSB_ENDPOINT_DIR_MASK) == LIBUSB_ENDPOINT_IN)
		memcpy(data, libusb_control_transfer_get_data(transfer),
			transfer->actual_length);
 
 
	libusb_free_transfer(transfer);
	return r;
}

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