The MIG Spartan-6 MCB design requires that specific trace matching guidelines be followed to ensure proper behavior in hardware. The trace length/matching guidelines are available in theSpartan-6 FPGA Memory Controller User Guide(UG388); see the"Designing with the MCB">"PCB Layout Considerations" section: http://www.xilinx.com/support/documentation/ip_documentation/ug388.pdf.
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Common Trace Matching Questions
The trace matching guidelines are established through characterization of high-speed operation. The tight requirements are required for guaranteed operation at maximum performance.
Currently, the MCBdesign does not include per-pit deskew.Therefore, adherence to the DQ/DQS trace matching is extremely important.
The package delay should be included when determining the effective trace length. Note that different parts in the same package have different internal package skew values. De-rate the minimum period appropriately in the MIG Controller Options page when different parts in the same package are used.The most accurate and recommended method for determining the delay is to use the L and C values for each pin from the IBIS models. The delay value is determined as sqrt(L C); see also(Xilinx Answer 34174).