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Copyright 1989 AT&T
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drv_usectohz - convert microseconds to clock ticks

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



clock_t drv_usectohz(clock_t microsecs);

Architecture independent level 1 (DDI/DKI).

microsecs

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).

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.

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

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

Writing Device Drivers

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.