[time-nuts] Re: UTC - A Cautionary Tale

Bill Hawkins bill at iaxs.net
Sat Jul 16 23:22:01 EDT 2005

Perhaps some of you didn't understand the paragraph on
process control systems, or perhaps you are still pondering.

Let me restate the solution for those who can only get UTC
but need monotonically increasing wall clock time.

Note that "you" is no one specific, just not me.

1. Provide your computer with the rate of UTC as a one second
tic or faster from a disciplined oscillator. Make this your
clock interrupt. Or read NTP on how to discipline a computer's
clock rate to 1 PPS.

2. Provide a rate adjustment for your computer clock, in seconds
per year with a resolution of .001 second per year, plus or minus.

3. In the interrupt routine, adjust the frequency. This can be
done by counting the fractions of the interrupt period such that
there is an overflow whenever the oscillation count must be
adjusted by one. I've seen the code, but I'll leave it to your

You now have an oscillator. How you initialize the counter (clock)
is up to you. Apparently you do not care about the correct time
of day.

4. When you receive notice of a pending leap second adjustment,
adjust the rate so that you will have added or subtracted one
second by the time of the update. You may then set the rate to
zero, since the frequency is correct or reduce the rate by half
in anticipation of the next notice.

If you absolutely must advance time at the rate of TAI, then
petition the governing body to destroy the meaning of UTC as civil
time in order to satisfy your petty annoyance. Petty, that is, in
comparison to the billions of people who like UTC the way it is.

You could set up your own distribution system for TAI, based on
the rate of UTC, if this list could get quieted down to where we
could talk about that.

Bill Hawkins

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