.\"     $NetBSD: microtime.9,v 1.21 2013/09/17 19:58:03 wiz Exp $
.\"
.\" Copyright (c) 1998 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jeremy Cooper.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.\" Copyright (c) 2000 Kelly Yancey
.\" All rights reserved.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
.\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
.\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
.\" ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
.\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
.\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
.\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
.\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
.\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
.\" SUCH DAMAGE.
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.\" $FreeBSD: src/share/man/man9/microtime.9,v 1.11 2005/10/13 16:01:28 jhb Exp $
.\"
.Dd May 13, 2013
.Dt MICROTIME 9
.Os
.Sh NAME
.Nm bintime ,
.Nm getbintime ,
.Nm microtime ,
.Nm getmicrotime ,
.Nm nanotime ,
.Nm getnanotime
.Nd get the current time
.Sh SYNOPSIS
.In sys/time.h
.Ft void
.Fo bintime
.Fa "struct bintime *bt"
.Fc
.Ft void
.Fo getbintime
.Fa "struct bintime *bt"
.Fc
.Ft void
.Fo "microtime"
.Fa "struct timeval *tv"
.Fc
.Ft void
.Fo getmicrotime
.Fa "struct timeval *tv"
.Fc
.Ft void
.Fo nanotime
.Fa "struct timespec *tsp"
.Fc
.Ft void
.Fo getnanotime
.Fa "struct timespec *tsp"
.Fc
.Sh DESCRIPTION
The
.Fn bintime
and
.Fn getbintime
functions store the system time as a
.Vt "struct bintime"
at the addresses specified by
.Fa bt .
The
.Fn microtime
and
.Fn getmicrotime
functions perform the same utility, but record the time as a
.Vt "struct timeval"
instead.
Similarly the
.Fn nanotime
and
.Fn getnanotime
functions store the time as a
.Vt "struct timespec" .
The structures are described in
.Xr timeval 3 .
.Pp
The
.Fn bintime ,
.Fn microtime ,
and
.Fn nanotime
functions
always query the timecounter to return the current time as precisely as
possible.
Whereas
.Fn getbintime ,
.Fn getmicrotime ,
and
.Fn getnanotime
functions are abstractions which return a less precise, but
faster to obtain, time.
.Pp
The intent of the
.Fn getbintime ,
.Fn getmicrotime ,
and
.Fn getnanotime
functions is to enforce the user's preference for timer accuracy versus
execution time.
They should be used where a precision of
.Pf 1/ Em HZ
(e.g., 10 msec on a
.Pf 100 Em HZ
machine, see
.Xr hz 9 )
is acceptable or where performance is priority.
.Pp
The system realtime clock is guaranteed to be monotonically increasing
at all times.
As such, all calls to these functions are guaranteed to return a system time
greater than or equal to the system time returned in any previous calls.
Comparable functions exist to retrieve the time elapsed since boot; see
.Xr microuptime 9 .
.Sh CODE REFERENCES
The implementation of the
.Fn microtime
family of functions is in
.Pa sys/kern/kern_tc.c
as a part of the
.Xr timecounter 9
framework.
.Pp
The implementation of the time counter sources used by the
.Xr timecounter 9
is machine dependent,
hence its location in the source code tree varies from architecture to
architecture.
.Sh SEE ALSO
.Xr settimeofday 2 ,
.Xr bintime_add 9 ,
.Xr inittodr 9 ,
.Xr time_second 9 ,
.Xr tvtohz 9
.Sh AUTHORS
This manual page was written by
.An Jeremy Cooper
and
.An Kelly Yancey Aq Mt kbyanc@posi.net .
.Sh CAVEATS
Despite the guarantee that the system realtime clock will always be
monotonically increasing,
it is always possible for the system clock to be manually reset by the
system administrator to any date.