Setup vs Hold

Setup as a Maximum-Delay Problem

Setup analysis asks whether the data path takes too long to satisfy the required timing relationship.

Hold as a Minimum-Delay Problem

Hold analysis asks whether new data can reach the destination too quickly after the capturing edge.

Maximum-Delay Problem

A timing problem caused by data taking too long to complete the required path.

Minimum-Delay Problem

A timing problem caused by new data propagating too quickly to the destination.

Too-Late Data

Characteristic timing danger associated with a setup failure.

Too-Early New Data

Characteristic timing danger associated with a hold failure.

Hold Analysis

Checks whether new data can reach the destination too quickly after the capturing edge.

Hold Interval

The required interval after the capture edge during which the destination must preserve the just-captured value.

Too-Fast New Data Path

A path that allows new data to reach the destination early enough to create a possible hold violation.

Capture Edge → Required Hold Interval

After the capturing edge, the destination must preserve the just-captured value for the required hold interval.

Setup Failure vs Hold Failure

Setup failure is generally caused by excessive path delay; hold failure is caused by insufficient path delay.

Setup Timing Question

Can the required data arrive soon enough?

Hold Timing Question

Can new data be prevented from arriving too soon?

Setup Timing Concern

Whether the path is fast enough to meet its maximum-delay requirement.

Hold Timing Concern

Whether the path has enough minimum delay to preserve the required post-capture relationship.

Why a Slower Clock Can Help Setup

Increasing the allowed clock period can provide more time for a maximum-delay setup path to complete.

Why a Slower Clock Does Not Automatically Fix Hold

A hold problem occurs around the same capture edge rather than at the next clock-period boundary.

Hold Violation Is Not Primarily a Next-Cycle Problem

The minimum-delay requirement concerns what happens immediately around the capture edge, so simply moving the next clock edge later does not inherently repair it.

Clock-Period Relaxation vs Hold

Relaxing the requested clock period changes the next-cycle timing budget but does not automatically correct an excessively fast minimum-delay path.

Setup Side of Closure

The maximum-delay side of timing closure.

Hold Side of Closure

The minimum-delay side of timing closure.

Both Sides of Timing Closure

A physically timing-healthy design must satisfy the relevant setup requirements and the relevant hold requirements.

Clean Setup Alone ≠ Timing Closure

A design is not physically timing-healthy merely because its setup timing passes; relevant hold requirements must also pass.

Setup Pass + Hold Fail

The design has not achieved timing closure because one required side of the timing contract still fails.

Setup Pass + Hold Pass

The relevant maximum-delay and minimum-delay timing requirements are both satisfied.

Timing Closure Requires More Than Positive Setup Margin

Positive setup results do not substitute for checking the relevant hold requirements.

Setup Remedy Reasoning

When setup fails, investigate why too much delay or work exists in the required path.

Hold Remedy Reasoning

When hold fails, reason about why the new data path is too fast rather than assuming that additional clock period will solve it.

Maximum Delay vs Minimum Delay

The fundamental implementation distinction that separates setup-timing reasoning from hold-timing reasoning.