Manual Pages for UNIX Operating System command usage for man drv_usecwait

Kernel Functions for Drivers                     drv_usecwait(9F)



NAME
     drv_usecwait - busy-wait for specified interval

SYNOPSIS
     #include 
     #include 



     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 ini-
     tialization.


     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,  inter-
     rupt, or kernel context.

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


     Writing Device Drivers





SunOS 5.11          Last change: 16 Jan 2006                    1






Kernel Functions for Drivers                     drv_usecwait(9F)



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.

















































SunOS 5.11          Last change: 16 Jan 2006                    2