What is data required time?
From PDVerse STA Mentor Guide · pdVerse Mentor Guide
Short Answer
Data required time is the latest moment (for a setup check) or earliest moment (for a hold check) that a signal is allowed to arrive at its destination.
Example
For a setup check with a 1000 ps period, a 60 ps setup requirement, and 40 ps of clock uncertainty, the data required time works out to 1000 - 60 - 40 = 900 ps.
Why It Matters
Required time is the other half of every timing check — the tool derives it from the capture clock edge adjusted for the capturing flop's setup or hold requirement, clock skew, and clock uncertainty, then compares it to arrival time to get slack.
Equation
data required = period - setup - uncertainty = 1000 - 60 - 40 = 900Mentor Note — Common Mistake
Assuming required time is a fixed number independent of the clock — in reality it shifts with skew and uncertainty, so the 'deadline' for data to arrive can move depending on how the clock behaves at the capture flop.
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