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When I run timequest and report datasheet, I get negative values for t_h; i.e. Hold Times. Is this reasonable?
For some synthesis, t_h is positive, when I change settings t_h becomes negative. Does it mean something is wrong?
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negative slack = failure
You should not just play with settings to get a pass but rather set it to your io correctly.
Your design is really too complicated for a beginner to get i right because your clk is opposite data direction and you have inserted a PLL with phase shift. I suggest you first remove the pll and compute your settings then if necessary add pll
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