Asynchronous Clock Groups - 2023.2 English

Vivado Design Suite User Guide: Using Constraints (UG903)

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2023.2 English

Asynchronous clocks and unexpandable clocks cannot be safely timed. The timing paths between them can be ignored during analysis by using the set_clock_groups command.

Important: The set_clock_groups command has higher priority over the regular timing exceptions. If you need to constrain and report some paths between asynchronous clocks, you must use the timing exceptions only, and not set_clock_groups.

Asynchronous Clock Groups Examples

  • The primary clock clk0 is defined on an input port and reaches an MMCM which generates the clocks 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.