2.8.2 FDDR Subsystem

The FDDR subsystem has one interface to the DDR. This is a multiplexed interface from the FPGA fabric, which can be configured as either a single AXI 64-bit bus or two 32-bit AHB-Lite buses. There is also a 16-bit APB configuration bus, which is used to initialize the majority of the internal registers within the FDDR subsystem after reset. This APB configuration bus can be mastered by a host in the FPGA fabric.