Asynchronous Clock Groups - Asynchronous Clock Groups - 2026.1 English

Asynchronous Clock Groups - Asynchronous Clock Groups - 2026.1 English - UG903

Vivado Design Suite User Guide: Using Constraints (UG903)

Document ID

UG903

Release Date

2026-07-01

Version

2026.1 English

Treat asynchronous and unexpandable clocks as untimed. Use set_clock_groups to ignore paths between them during analysis.

Important: set_clock_groups takes priority over timing exceptions. If you need to constrain and report specific paths between asynchronous clocks, use timing exceptions only. Do not use set_clock_groups.

Asynchronous Clock Groups Examples

A primary clock clk0 is defined on an input port and reaches an MMCM that generates usrclk and itfclk.
A second primary clock clk1 is a recovered clock defined on the output of a GTP instance and reaches a second MMCM which generates the clocks gtclkrx and gtclktx.