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SubjectRe: [PATCH RFC V2 3/6] time: keep track of the pending utc/tai threshold
On 05/22/2012 10:39 AM, Richard Cochran wrote:
> On Mon, May 21, 2012 at 09:08:15PM +0200, Richard Cochran wrote:
>> On Mon, May 21, 2012 at 11:09:51AM -0700, John Stultz wrote:
>>> On 05/18/2012 07:09 AM, Richard Cochran wrote:
>>>> + /* Tracks where we stand with regard to leap the second epoch. */
>>>> + enum {
>>>> + LEAP_IDLE,
>>>> + LEAP_INS_PENDING,
>>>> + LEAP_INS_DONE,
>>>> + LEAP_DEL_PENDING,
>>>> + LEAP_DEL_DONE,
>>>> + } leap_state;
> ...
>
>> I don't think I am explaining this very well. I will try again to make
>> it clear using a table or something later on.
> The following table illustrates what happens around a (fictitious)
> leap second. Imagine a new epoch will occur at UTC time value 10 and
> the new TAI - UTC offset will be 2 seconds. The columns of the table
> show the values of the relevant time variables.
>
> U: UTC time
> CODE: NTP time code
> T: TAI - UTC offset
> P: pending (explained below)
>
> U CODE T P
> --------------------
> 1 INS 1 1 leap second sheduled
> --------------------
> 2 INS 1 1
> --------------------
> ...
> --------------------
> 8 INS 1 1
> --------------------
> 9 INS 1 1
> --------------------
> | 10 OOP 1 1 leap second, 1st tick
> |~~~~~~~~~~~~~~~~~~~
> | 9 2 0 leap second, 2nd and subsequent ticks
> --------------------
> 10 WAIT 2 0 new epoch
> --------------------
> 11 WAIT 2 0

Not sure I'm still following.

It seems currently we have:

U CODE T
----------------
9 INS 1
----------------
10 INS 1 pre tick, post leap second edge (this is the technically incorrect interval)
~~~~~~~~~~~~~~~~
9 OOP 2 post tick, post leap second edge
----------------
10 WAIT 2 new epoch

If you're trying to correct the pre-tick, post leap second edge, the above provides all you need.

In the adjtimex code, all you have to do is:


if (unlikely(CODE == INS&& U == 10))
/*note, we're not modifying state here, just returning corrected local values*/
return (U-1, OOP, T+1);

return (U,CODE, T);


Since when the tick triggers, we'll move the CODE state appropriately.

Or am I still missing something?

thanks
-john



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