Wed Aug 10 13:01:26 EDT 2016

Double DFF to combat metastability

The rationale:

- If there is an edge that causes a timing violation, it is assumed
  that the oscillation that this might cause in the first DFF will
  settle before it would violate the setup time of the second DFF.

- In case the first DFF settles to the incorrect edge, it will pass
  through the correct edge on the next clock.