Constraints on bitwiz

constraint-lint

Thu, 01 Jan 2026 00:00:00 +0000

The Problem

Your XDC file is code. Vivado doesn’t lint it.

create_clock -name clk156 -period 6.400 [get_ports clk_156]

The port is clk156. The clock attaches to nothing. Vivado warns once. It disappears into 200k lines of logs.

Your constraint file says the clock exists. Your log has one warning: no valid objects matched. WNS is meaningless because the domain you thought you constrained doesn’t exist. You find out in the lab.

What constraint-lint Does

Lint for XDC/SDC. Runs in CI. Turns constraint warnings into hard failures.

Constraints: The Contract You Forgot to Sign

Tue, 23 Dec 2025 15:04:00 +0000

Timing Series: Part 1 of 6

Previous: Your FPGA Lives a Lifetime While You Blink

Signoff Gates: Build Must Fail If…

Before reading further, know this: your build should fail if any of these checks fail.

Gate 1: Unconstrained endpoints must be zero

check_timing -verbose
report_exceptions -verbose

Fail if: Any constraint-related issue about clocks, unconstrained endpoints, or missing I/O delays. Also fail if any exception matches zero objects (silent no-op) or hits an unexpectedly large set.