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
clk0is defined on an input port and reaches an MMCM which generates the clocksusrclkanditfclk. - A second primary clock
clk1is a recovered clock defined on the output of a GTP instance and reaches a second MMCM which generates the clocksgtclkrxandgtclktx.