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)