'\" te
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.TH drv_usectohz 9F "24 Apr 2008" "SunOS 5.11" "Kernel Functions for Drivers"
.SH NAME
drv_usectohz \- convert microseconds to clock ticks
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <sys/ddi.h>



\fBclock_t\fR \fBdrv_usectohz\fR(\fBclock_t\fR \fImicrosecs\fR);
.fi

.SH INTERFACE LEVEL
.sp
.LP
Architecture independent level 1 (DDI/DKI).
.SH PARAMETERS
.sp
.ne 2
.mk
.na
\fB\fImicrosecs\fR\fR
.ad
.RS 13n
.rt  
The number of microseconds to convert.
.RE

.SH DESCRIPTION
.sp
.LP
The \fBdrv_usectohz()\fR function converts a length of time expressed in
microseconds to a number of system clock ticks. The time arguments to
\fBtimeout\fR(9F) and \fBdelay\fR(9F) are expressed in clock ticks.
.sp
.LP
The \fBdrv_usectohz()\fR function is a portable interface for drivers to make
calls to \fBtimeout\fR(9F) and \fBdelay\fR(9F) and remain binary compatible
should the driver object file be used on a system with a different clock speed
(a different number of ticks in a second).
.SH RETURN VALUES
.sp
.LP
The value returned is the number of system clock ticks equivalent to the
\fImicrosecs\fR argument. No error value is returned. If the clock tick
equivalent to \fImicrosecs\fR is too large to be represented as a
\fBclock_t\fR, then the maximum \fBclock_t\fR value will be returned.
.SH CONTEXT
.sp
.LP
The \fBdrv_usectohz()\fR function can be called from user, interrupt, or kernel
context.
.SH SEE ALSO
.sp
.LP
\fBdelay\fR(9F), \fBdrv_hztousec\fR(9F), \fBtimeout\fR(9F)
.sp
.LP
\fIWriting Device Drivers\fR
.SH NOTES
.sp
.LP
If the \fImicrosecs\fR argument to \fBdrv_usectohz()\fR is less than
\fBdrv_hztousec\fR(9F), \fBdrv_usectohz()\fR returns one tick. This, coupled
with multiplication, can result in significantly longer durations than
expected. For example, on a machine where \fBhz\fR is 100, calling
\fBdrv_usectohz()\fR with a \fImicrosecs\fR value less than 10000 returns a
result equivalent to 10000 (1 tick). This type of mistake causes code such
as"5000 * drv_usectohz(1000)" to compute a duration of 50 seconds instead of
the intended 5 seconds.