drv_usecwait man page on SmartOS

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       drv_usecwait - busy-wait for specified interval

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

       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‐
       nel context.

       delay(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)

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