NetBSD/share/man/man9/microtime.9

.\"     $NetBSD: microtime.9,v 1.21 2013/09/17 19:58:03 wiz Exp $
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.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jeremy Cooper.
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.\" Copyright (c) 2000 Kelly Yancey
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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.