unruh wrote:
Uh, no. There is no way of getting the signal into the computer with
No pure sw way, no.
nanosecond accuracy. 1usec is about it. The interrupt service routines, if you use a specialised driver for some interrupt driven card, will take about 1usec to service the interrupt. Thus while the card may deliver a pulse whose leading edge is within say 50ns of the correct time that is irrelevant if the computer itself cannot respond fast enough. But I agree, with a GPS you can get usec accuracy in the time delivered for less than $100.
Add some extra hw, in the form of a very good crystal (surplus Rb) and a hw counter which starts to run on the PPS signal, so that the sw can query it to determine how much interrupt latency we got this time, and you get a FreeBSD box down in the dual-digit nanoseconds.
Google phk! Terje -- - <Terje.Mathisen at tmsw.no> "almost all programming can be viewed as an exercise in caching" _______________________________________________ questions mailing list questions@lists.ntp.org http://lists.ntp.org/listinfo/questions
