Hi The issue there is the clock on the external inputs. The interupts can't directly hit the TSC. They only get into the device after being clocked by a much slower clock.
Bob On Jul 2, 2013, at 3:32 AM, mike cook <[email protected]> wrote: > > Le 2 juil. 2013 à 02:52, Bob Camp a écrit : > >> Hi >> > < snip> >> >> The reference I was making was to a "pie in the sky" 1.8 GHz clocked timer >> integrated into a CPU chip. That would let you come up with ~ 600 ps timing >> directly. Since it would be both unusual and very fast, a driver >> (potentially tightly linked to the kernel) would be needed. That's not a >> trivial thing…. > > Is that what you really want? In most modern x86 CPU's you have a TSC which > is a 64bit counter incremented at the cpu clock cycle speed . You can capture > that with a single instruction. NTP uses that if it is available. So to get > an accurate TI you just take 2 samples and subtract. You just need to take > into account interrupt handling latency. I don't think this is available in > ARM under that name, but there is a cycle count register CCNT which does the > same thing. I think it is 64 bit as well. > > Mike > >> >>> >>> >>> -- >>> These are my opinions. I hate spam. >>> >>> >>> >>> _______________________________________________ >>> time-nuts mailing list -- [email protected] >>> To unsubscribe, go to >>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>> and follow the instructions there. >> >> _______________________________________________ >> time-nuts mailing list -- [email protected] >> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> and follow the instructions there. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
