delay(9) [netbsd man page]

DELAY(9)						   BSD Kernel Developer's Manual						  DELAY(9)

NAME

     delay, DELAY -- microsecond delay

SYNOPSIS

     #include <machine/param.h>

     void
     delay(unsigned int us);

     void
     DELAY(unsigned int us);

DESCRIPTION

     Wait approximately us microseconds.

     The delay is implemented as a machine loop, preventing events other than interrupt handlers for unmasked interrupts to run.  DELAY() is reen-
     trant (doesn't modify any global kernel or machine state) and is safe to use in interrupt or process context.

     For long delays, condition variables should be considered, however they can only be used from process context and their resolution is limited
     by the system clock frequency.

SEE ALSO

     condvar(9), hz(9), kpause(9)

BSD
								   July 20, 2011							       BSD

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

       drv_usecwait()  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) may only be invoked
       from user 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

       drv_usecwait() can be called from user or interrupt 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.   drv_usecwait() does not mask out interrupts.

SunOS 5.10							    12 Nov 1992 						  drv_usecwait(9F)