How do I synchronize gray code counts safely across asynchronous clock domains?

--- Quote Start ---

Unfortunately, set_max_skew pays attention to the set_false_path. Because of the set_false_path, Timequest will say there is nothing to report in the "Report Max Skew Summary". The set_max_delay would be correct, but there is no way to say "datapath_only" and have it ignore the clock trees.

--- Quote End ---

First you may remove set_false_path and ignore any reported violations or set to some high multicycle.

second, this is an altera example that involves data path only:

# Create a max skew constraint that includes only data path arrival

set_max_skew -from [get_keepers inst1|*] -to [get_keepers inst2|*] 0.200 -exclude { from_clock to_clock clock_uncertainty }