I could manage to assign IP address to the Arduino ethernet shield mounted on Papilio Duo board, But when I tried to establish communication using TCP/IP, collision was detected by the ethernet shield. I think it must be because of the common SPI bus shared by both AVR microcontroller and Xilinx FPGA. Is there any work-around solution of the problem? I used Ethernet library from Arduino IDE. At present Xilinx FPGA is disabled, but in next stage I will be using wishbone bus shared registers.