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 DriversNOTES
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)
