Clock-skew calculation

tffpd(min) + tcomb(min)  thold  tskew(max) > 0
First two terms are minimum time after clock edge for a D input to change
Hold time is earliest time that the input may change
Clock skew subtracts from the available hold-time margin
Compensating for clock skew:
- Longer flip-flop propagation delay
- Explicit combinational delays
- Shorter (even negative) flip-flop hold times