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Add clarifications about the information that ntp_gettime returns.

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TAI is a timescale, just like UTC.  The tai field returns the offset
between the two, and isn't really used for precision time keeping.
Explain in brief what a positive and a negative leap seconds are.  Add
some URLs to very useful web pages about time and time keeping for
more information on using this API.

Reviewed by: phk
This commit is contained in:
Warner Losh 2003-06-21 20:27:54 +00:00
parent 9581ecbd72
commit f1fe8d5bac
1 changed files with 18 additions and 8 deletions
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26
lib/libc/sys/ntp_gettime.2
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@ -25,7 +25,7 @@
.\"
.\" $FreeBSD$
.\"
.Dd April 1, 2003
.Dd June 21, 2003
.Dt NTP_GETTIME 2
.Os
.Sh NAME
@ -57,7 +57,7 @@ struct ntptimeval {
struct timespec time; /* current time (ns) (ro) */
long maxerror; /* maximum error (us) (ro) */
long esterror; /* estimated error (us) (ro) */
long tai; /* TAI offset */
long tai; /* TAI-UTC offset */
int time_state; /* time status */
};
.Ed
@ -71,9 +71,14 @@ Maximum error in microseconds (read-only).
.It Va esterror
Estimated error in microseconds (read-only).
.It Va tai
Temps Atomique International (French for International Atomic Time),
measures real time.
Used for acute time measurements.
Offset in seconds between the TAI and UTC time scales.
This offset is published twice a year and is an integral number of
seconds between TAI (which does not have leap seconds) and UTC (which
does).
.Xr ntpd 8
or some other agent maintains this value.
A value of 0 means unknown.
As of the date of the manual page, the offset is 32 seconds.
.It Va time_state
Current time status.
.El
@ -86,9 +91,11 @@ Possible states of the clock are:
.It Dv TIME_OK
Everything okay, no leap second warning.
.It Dv TIME_INS
Insert leap second warning.
Positive leap second warning.
At the end of the day, an additional second will be inserted after 23:59:59.
.It Dv TIME_DEL
Delete leap second warning.
Negative leap second warning.
At the end of the day, 23:59:59 is skipped.
.It Dv TIME_OOP
Leap second in progress.
.It Dv TIME_WAIT
@ -98,7 +105,10 @@ Clock not synchronized.
.El
.Sh SEE ALSO
.Xr ntp_adjtime 2 ,
.Xr ntpd 8
.Xr ntpd 8 ,
.Dq Li http://www.bipm.fr/enus/5_Scientific/c_time/time_1.html ,
.Dq Li http://www.boulder.nist.gov/timefreq/general/faq.htm ,
.Dq Li ftp://time.nist.gov/pub/leap-seconds.list
.Sh AUTHORS
This manual page was written by
.An Tom Rhodes Aq trhodes@FreeBSD.org .