The mapping is done by the five last significant bits in the registers CY_U3P_PIB_GPIF_THREAD_CONFIG_ADDRESS(0...3) in the GPIF descriptors. There you can map one of the 32 sockets to each hardware thread.
Hi，Chris R. Thanks for your answer.
Do you know which document could I found the detail specification of the GPIFII config registers?
There is no document but the header file. Take a look into it by clicking "Go to declaration" in Eclipse.