I’ve got a SASEBO-W board, which has a FPGA & a FT2232H for high-speed USB comms. I was seeing errors on the high-speed USB device, and couldn’t figure out why:
The SASEBO-W is a multi-purpose board including a Xilinx LX150 Spartan 6 FPGA and a FTDI FT2232H USB interface. One use of the board is for measuring the power consumption of the FPGA and using that power consumption to perform power analysis attacks. I believe for this reason the ground planes are split, to facilitate making those measurements.