We really only want to apply the CDC constraints if the clocks are actually
asynchronous. Unfortunately we can't use if ... inside a xdc script. But we
can use expr which has support for a ? b : c if-like expression. We can use
that to create helper variables that contains valid clock when the clock
domains are asynchronous or {} if they are not. Passing {} as
set_false_path/set_max_delay as either the source or destination will cause
it to abort and no constraints will be added.
Also add -quiet parameters to avoid generating warning if the constraints
could not be added.
Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
42a9da0659