even if there's nothing else in the design, you won't be able to make an On Chip Memory that uses the entire FPGA. this has to do with how the fitter stitches together M9K
you'll probably need to increment the On Chip Memory size (in steps equal to an M9K) to find the max size you can do in the FPGA, or use pencil and paper after you figure out how the tool is placing the RAM
