Zybo build utilization of fpga

Question

I would like to know how much resources of Zybo fpga board are utilized if we use the stock implementation of Rocket core(with FP). If it is already 60% then it probably would not make sense to start with Zybo board if I plan to add some instructions.

Answer 1

I can't speak exactly to a Zynq zybo FPGA board, but I can provide some numbers for a Zynq zedboard I use.

Utilization:
  FF - 22%
  LUT - 59%
  BRAM - 15% (easily adjustable and dependent on cache sizing)

However, the important thing to remember is the Rocket core itself is only a small part of the FPGA area - it's the uncore and surrounding I/O infrastructure that maps poorly to FPGA resources and takes up most of the LUT resources.

In short, you should easily be able to add new instructions to the core and see little to no change in FPGA resource utilization. Unless of course your new instructions require significant resources that map poorly to FPGAs (e.g., enormous shifters or huge, highly ported register files).