DRV_USECWAIT(9F)DRV_USECWAIT(9F)NAMEdrv_usecwait - busy-wait for specified interval
void drv_usecwait(clock_t microsecs);
Architecture independent level 1 (DDI/DKI).
The number of microseconds to busy-wait.
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
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.
The drv_usecwait() function can be called from user, interrupt, or ker‐
SEE ALSOdelay(9F), timeout(9F), untimeout(9F)
Writing Device Drivers
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.
Jan 16, 2006 DRV_USECWAIT(9F)