How to constraining clocks in dcfifo

Thanks for the info.

You'er right in what you say but I haven't found it to work. The set false paths give warnings, when you re-run the design, saying that the paths can't be found.

If I leave out some clock group constraints then it tries to constrain paths with ridiculous timing constraints. If you look at what it was trying to do, it's trying to constrain the pointers in the FIFO at with a timing constraint of 0.8ns! The clock is 6.4ns.

So, something isn't working. Perhaps because the false paths aren't working, there is a knock on effect with everything else.