On Tue, Dec 21, 2010 at 4:56 PM, Richard Cochran
<[email protected]> wrote:
> Can you please elaborate?
The timex.constant is defined as equal to the binary logarithm of the
reciprocal of
the natural frequency minus SHIFT_PLL. In other words, the following
equation holds:
log2(natural frequency) + time_constant + SHIFT_PLL = 0,
which means that decreasing time_constant increases natural frequency
exponentially.
And since a larger natural frequency gives a smaller settling time, a
sufficiently
large negative time_constant results in immediate time step, at least in theory.
> I don't see any way to use timex.constant with ADJ_OFFSET in order to
> correct a time offset.
How about this?
if (txc->modes & ADJ_OFFSET) {
if (txc->constant == INT32_MIN) {
/* step time */
} else {
/* slew time */
}
}
> The 'time_constant' in kernel/time/ntp.c is
> restricted to the interval [0..MAXTC], and MAXTC is 10 in timex.h.
Then let's just ignore the restriction. (It's possible by setting the
timex.constant
without setting the ADJ_TIMECONST flag.)
That said, I'm somehow against the idea of using the adjtimex syscall
for that purpose.
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