Re: [chrony-users] GPS / Chrony NTP server config questions

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On Thu, 16 Nov 2017, Denny Page wrote:

Interrupt latency for character devices in Linux is 6-7 us, even with no other activity. You

It has been a while but I ran tests on a system in which I changed the state
of a parallel port pin and fed that into an interrupt grabbing the system time
just before toggling the pin, and the time when the interrupt service routine
got the interrupt. The latency was of the
order of 1us, not 7. Now that was on an older machine with the 1us, not the ns
clock. I have not tried this recently but would be surprized if the time was
worse now.

can get better than this using a gpio and spinning on it, but I haven’t seen anyone do this

Well, that is unclear, and hugely expensive in terms of taking up the time of
the cpu.

with with serial pps.

      On Nov 16, 2017, at 09:57, Bill Unruh <unruh@xxxxxxxxxxxxxx> wrote:

The PPS accuracy is largely determined by the interrupt handling time, which
is something like a usec. It depends, so that if the the pps comes in when the
computer is reading a disk (which used non-interruptable interrupts) it will
be delayed by many microseconds.

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