Understanding Timing Analysis

Sun, 28 Dec 2025 05:25:00 +0000

Timing Series: Part 2 of 6

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The Path You Can’t Explain

You’re staring at this:

Slack (VIOLATED) : -0.247ns (required time - arrival time)
 Source: tx_reg[7]/Q
 Destination: fifo_wr_reg/D
 Path Group: clk_156
 Path Type: Setup (Max at Slow Process Corner)
 Requirement: 6.400ns
 Data Path Delay: 5.847ns (logic 1.423ns (24.3%) route 4.424ns (75.7%))
 Logic Levels: 4 (LUT6=3 CARRY4=1)
 Clock Path Skew: -0.360ns (DCD - SCD)
 Clock Uncertainty: 0.400ns

Data path is 5.847 ns. Period is 6.4 ns. You subtract and get 0.553 ns. That number is meaningless as “margin” because it ignores clock-to-source, clock-to-dest, setup, and uncertainty.

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Understanding Timing Analysis

The Path You Can’t Explain