DRV_USECTOHZ(9F) Kernel Functions for Drivers DRV_USECTOHZ(9F)

NAME

drv_usectohz - convert microseconds to clock ticks

SYNOPSIS

#include <sys/types.h>
#include <sys/ddi.h>


clock_t drv_usectohz(clock_t microsecs);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI).

PARAMETERS

microsecs
The number of microseconds to convert.

DESCRIPTION

The drv_usectohz() function converts a length of time expressed in
microseconds to a number of system clock ticks. The time arguments to
timeout(9F) and delay(9F) are expressed in clock ticks.


The drv_usectohz() function is a portable interface for drivers to make
calls to timeout(9F) and delay(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).

RETURN VALUES

The value returned is the number of system clock ticks equivalent to the
microsecs argument. No error value is returned. If the clock tick
equivalent to microsecs is too large to be represented as a clock_t, then
the maximum clock_t value will be returned.

CONTEXT

The drv_usectohz() function can be called from user, interrupt, or kernel
context.

SEE ALSO

delay(9F), drv_hztousec(9F), timeout(9F)


Writing Device Drivers

NOTES

If the microsecs argument to drv_usectohz() is less than
drv_hztousec(9F), drv_usectohz() returns one tick. This, coupled with
multiplication, can result in significantly longer durations than
expected. For example, on a machine where hz is 100, calling
drv_usectohz() with a microsecs 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.


April 24, 2008 DRV_USECTOHZ(9F)