I have built a ATMega32u4-AU custom board (8Mhz Ceramic Resonators, 3.3V), after set the fuse: Fuse High Byte: 1001 1001 (0x99) Fuse Low Byte: 0101 1110 (0x5E) Extended Fuse Byte: 1111 0011 (0XF3), and downloaded bootloader to the chip, the device manager still shows "Unknown USB device", I cannot find which step I did wrong, please kindly point out. Many thanks.