We care about time. An ongoing effort is to improve the quality of timestamp available to IP cores inside an FPGA to sub-nanosecond precision. One way forward is to use a stable, but not terribly accurate, on-board XO; and then to discipline it to a highly-accurate, but transient, reference from a GPS. Our approach uses a PI servo that is smart about when to freewheel. No magic. Just math.
Agilent 53230A 20pS Counter/Timer