1. The user needs to obtain the usb device name to determine whether it is our printer

2. code

public String getProductName(){
		byte[] rawDescs = mUsbDeviceConnection.getRawDescriptors();
		String manufacturer = "", product = "";
		try
		{
			byte[] buffer = new byte[255];
			int idxMan = rawDescs[14];
			int idxPrd = rawDescs[15];
			Logger.i("index",idxMan);

			int rdo = mUsbDeviceConnection.controlTransfer(UsbConstants.USB_DIR_IN
							| UsbConstants.USB_TYPE_STANDARD, STD_USB_REQUEST_GET_DESCRIPTOR,
					(LIBUSB_DT_STRING << 8) | idxMan, 0, buffer, 0xFF, 0);
			manufacturer = new String(buffer, 2, rdo - 2, "UTF-16LE");

			rdo = mUsbDeviceConnection.controlTransfer(UsbConstants.USB_DIR_IN
							| UsbConstants.USB_TYPE_STANDARD, STD_USB_REQUEST_GET_DESCRIPTOR,
					(LIBUSB_DT_STRING << 8) | idxPrd, 0, buffer, 0xFF, 0);
			product = new String(buffer, 2, rdo - 2, "UTF-16LE");


		} catch (Exception e)
		{
			e.printStackTrace();
			Logger.e(e.getMessage());
		}

		Logger.i("","Manufacturer:" + manufacturer + "\n");
		Logger.i("","Product:" + product + "\n");
		Logger.i("","Serial#:" + mUsbDeviceConnection.getSerial() + "\n");
		return product.trim()+manufacturer.trim();
	}

3. The description of controltransfer method is shown in the two figures. The first parameter refers to whether you are reading or writing. 2. What content you want to read or write. 3. The index of the field in the content structure. 4. What offset to start reading and writing. 5. The read container or the write data. 6. Length https://blog.csdn.net/obanaganastar/article/details/72866260

4. When tracking this method, it will break when it comes to here, so I guess the above 3 parameters

int usb_device_control_transfer(struct usb_device *device,
575                            int requestType,
576                            int request,
577                            int value,
578                            int index,
579                            void* buffer,
580                            int length,
581                            unsigned int timeout)
582{
583    struct usbdevfs_ctrltransfer  ctrl;
584
585    // this usually requires read/write permission
586    if (!usb_device_reopen_writeable(device))
587        return -1;
588
589    memset(&ctrl, 0, sizeof(ctrl));
590    ctrl.bRequestType = requestType;
591    ctrl.bRequest = request;
592    ctrl.wValue = value;
593    ctrl.wIndex = index;
594    ctrl.wLength = length;
595    ctrl.data = buffer;
596    ctrl.timeout = timeout;
597    return ioctl(device->fd, USBDEVFS_CONTROL, &ctrl);
598}
//Then call the kernel method.
#define USBDEVFS_CONTROL           _IOWR('U', 0, struct usbdevfs_ctrltransfer)

5. results

ps: because most of the underlying software of the printer is written by Epson, the product s used can be the same, and three splices are needed for comparison