'\" te
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.\" Copyright 1989 AT&T
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.TH DRV_HZTOUSEC 9F "Jan 16, 2006"
.SH NAME
drv_hztousec \- convert clock ticks to microseconds
.SH SYNOPSIS
.LP
.nf
#include <sys/types.h>
#include <sys/ddi.h>



\fBclock_t\fR \fBdrv_hztousec\fR(\fBclock_t\fR \fIhertz\fR);
.fi

.SH INTERFACE LEVEL
.sp
.LP
Architecture independent level 1 (DDI/DKI).
.SH PARAMETERS
.sp
.ne 2
.na
\fB\fIhertz\fR\fR
.ad
.RS 9n
The number of clock ticks to convert.
.RE

.SH DESCRIPTION
.sp
.LP
The \fBdrv_hztousec()\fR function converts into microseconds the time expressed
by \fIhertz\fR, which is in system clock ticks.
.sp
.LP
The kernel variable \fBlbolt\fR, whose value should be retrieved by calling
\fBddi_get_lbolt\fR(9F), is the length of time the system has been up since
boot and is expressed in clock ticks. Drivers often use the value of
\fBlbolt\fR before and after an \fBI/O\fR request to measure the amount of time
it took the device to process the request. The \fBdrv_hztousec()\fR function
can be used by the driver to convert the reading from clock ticks to a known
unit of time.
.SH RETURN VALUES
.sp
.LP
The number of microseconds equivalent to the \fIhertz\fR parameter. No error
value is returned. If the microsecond equivalent to \fIhertz\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_hztousec()\fR function can be called from user, interrupt, or kernel
context.
.SH SEE ALSO
.sp
.LP
\fBddi_get_lbolt\fR(9F), \fBdrv_usectohz\fR(9F), \fBdrv_usecwait\fR(9F)
.sp
.LP
\fIWriting Device Drivers\fR