What is a hold check, and what is hold time?
From PDVerse STA Mentor Guide · pdVerse Mentor Guide
Short Answer
A hold check verifies that data launched by a clock edge does not arrive at the capturing flop too soon after that same edge — the data must stay stable until a hold time (Th) after the edge; it is a min-delay check that does not depend on the clock period at all.
Example
In a worked hold example on the same clock edge, data arrives at 85 ps while the required time is 75 ps, giving a hold slack of +10 ps, which passes — notice the period never appears anywhere in this calculation.
Why It Matters
Hold violations cannot be fixed by slowing the clock — that's why hold failures are silicon killers: a hold problem exists at every frequency and can only be fixed by adding delay to the too-fast path.
Equation
hold slack = arrival - requiredMentor Note — Common Mistake
Trying to fix a hold violation by lowering clock frequency, which does nothing, since the check is period-independent — the only real fix is inserting delay into the fast path.
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