Trace length variations cause data valid window variations between the signals, reducing margin. For example, DDR2-800 at 400 MHz has a data valid window that is smaller than 1,250 ps. Trace length skew or crosstalk can reduce this data valid window further, making it difficult to design a reliably operating memory interface. Ensure that the skew figure previously entered into the Intel® FPGA IP matches that actually achieved on the PCB, otherwise Quartus Prime timing analysis of the interface is accurate.
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