使用USB将Android连接到Rambo

Question

我尝试将我的archos Titanium HD连接到我的RAMBo（http://reprap.org/wiki/Rambo）。目前我可以连接到设备，我找到USB_DIR_IN，但当我从连接读取时，我得到null。我做错了什么？

public void onReceive(Context context, Intent intent) {
            EditText myfield = (EditText) findViewById(R.id.editText1);
            String action = intent.getAction();
            if (ACTION_USB_PERMISSION.equals(action)) {
                synchronized (this) {
                    UsbDevice device = (UsbDevice)intent.getParcelableExtra(UsbManager.EXTRA_DEVICE);

                    if (intent.getBooleanExtra(UsbManager.EXTRA_PERMISSION_GRANTED, false)) {
                        if(device != null){

                            myfield.setText(myfield.getText()+"start connection");
                            UsbInterface intf = device.getInterface(0);


                            UsbManager mUsbManager=(UsbManager) getSystemService(Context.USB_SERVICE);
                            UsbDeviceConnection connection = mUsbManager.openDevice(device); 

                            if(connection.claimInterface(intf, forceClaim)){


                                for(int i=0;i<intf.getEndpointCount();i++){
                                    UsbEndpoint endpoint = intf.getEndpoint(i); 

                                    if(endpoint.getDirection()== UsbConstants.USB_DIR_IN){
                                        myfield.setText(myfield.getText()+"endpoint zum lesen:"+i);


                                        int ret=connection.bulkTransfer(endpoint, mybytes, 20, TIMEOUT);

                                        myfield.setText(myfield.getText()+"ret"+ret+" "+Arrays.toString(mybytes)+"first read");


                                    }
                                    else if(endpoint.getDirection()==UsbConstants.USB_DIR_OUT){

                                        myfield.setText(myfield.getText()+"endpoint zum schreiben"+i);
                                    }
                                    else{
                                        myfield.setText(myfield.getText()+"irgendein endpoint");

                                    }
                                }
                            }
                            else{

                                myfield.setText(myfield.getText()+"verbindung nicht möglich");
                            }

                          //call method to set up device cmmunication
                       }
                    } 
                    else {
                        myfield.setText("Permission denied");
                        //Log.d(TAG, "permission denied for device " + device);
                    }
                }
            }
        }
    };