I have a little question about DDR3-IP core. my environment is ... FPGA: ArriaIIGX QuartusII: version 13.0 IP: DDR3-SDRAM controller with ALTMEMPHY v13.1 I have set 100MHz for "PLL reference clock frequency" . and memory clock frequency is 300MHz and I input 100MHz to pll_ref_clk pin as I set above. then this IP-core does not work ( init_done is stacking LOW ). I had no idea about this and tried many things. then I found that when I gave 50MHz clock to pll_ref_clk, DDR3-SDRAM works well. the "PLL reference clock frequency" is still 100MHz. I don't understand what happens. can anybody tell what do I miss? or is that correct?