Setup and Hold Checks · sta

Part 1 · Timing Paths and Checks · All levels

4topics
4lessons

Setup and hold are the two checks at the heart of STA. Setup asks whether data arrives early enough before the capture edge; hold asks whether it stays long enough after the edge it must not disturb. This topic derives both inequalities from the launch and capture edges, works numeric examples, and defines slack, WNS and TNS.

Lesson	After it you can...
Launch and Capture Edges	Name the launch and capture edge for any pair of flops.
Setup Check Derivation	Write and evaluate the setup inequality with latencies and uncertainty.
Hold Check Derivation	Write and evaluate the hold inequality and say why the period does not appear for same-edge paths on one clock.
Slack and Criticality	Compute slack, WNS and TNS from a list of endpoints.

Suggested order: the four lessons in page order. Setup, Hold and Slack gives the RTL designer's version of the same idea.

Check yourself Which check depends on the clock period, setup or hold?

Setup. Data has one full period (adjusted for the edge relationship) to arrive. Hold compares data launched at an edge with the capture of the previous data at the same edge, so for same-edge paths on one clock the period does not appear.

Up nextLaunch and Capture Edges

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