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

NAME

drv_usecwait - busy-wait for specified interval

SYNOPSIS

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


void drv_usecwait(clock_t microsecs);

INTERFACE LEVEL

Architecture independent level 1 (DDI/DKI).

PARAMETERS

microsecs
The number of microseconds to busy-wait.

DESCRIPTION

The drv_usecwait() function gives drivers a means of busy-waiting for
a specified microsecond count. The amount of time spent busy-waiting
may be greater than the microsecond count but will minimally be the
number of microseconds specified.


delay(9F) can be used by a driver to delay for a specified number of
system ticks, but it has two limitations. First, the granularity of
the wait time is limited to one clock tick, which may be more time
than is needed for the delay. Second, delay(9F) can be invoked from
user or kernel context and hence cannot be used at interrupt time or
system initialization.


Often, drivers need to delay for only a few microseconds, waiting for
a write to a device register to be picked up by the device. In this
case, even in user context, delay(9F) produces too long a wait
period.

CONTEXT

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

SEE ALSO

delay(9F), timeout(9F), untimeout(9F)


Writing Device Drivers

NOTES

The driver wastes processor time by making this call since
drv_usecwait() does not block but simply busy-waits. The driver
should only make calls to drv_usecwait() as needed, and only for as
much time as needed. The drv_usecwait() function does not mask out
interrupts.

January 16, 2006 DRV_USECWAIT(9F)