（二）绕线 Clk to fist sdram<=6000mil （clk 到第一个 SDRAM 走线的长度<=6000MIL） Clk to last sdram<=12000mil（clk 到第一个 SDRAM 走线的长度<=12000MIL） Clk pair to each sdram matched within<=2mil(时钟线到每一个SDRAM 差分对间的误差 <=2mil) 550MIL<=L5-L11<=750MIL L5-L11 matched within<=5mil（在做等长时，最好将clk 的L5-L11 做成同一个数值，小数点