opensolaris man page for ddi_periodic_add

ddi_periodic_add(9F)					   Kernel Functions for Drivers 				      ddi_periodic_add(9F)

NAME
       ddi_periodic_add - issue nanosecond periodic timeout requests

SYNOPSIS
       #include <sys/dditypes.h>
       #include <sys/sunddi.h>

       ddi_periodic_t
       ddi_periodic_add(void (*func)(void *), void arg,
	    hrtime_t interval, int level);

INTERFACE LEVEL
       Solaris DDI specific (Solaris DDI)

PARAMETERS
       func	   The callback function is invoked periodically in the specified interval. If the argument level is zero, the function is invoked
		   in kernel context. Otherwise, it's invoked in interrupt context at the specified level.

       arg	   The argument passed to the callback function.

       interval    Interval time in nanoseconds.

       level	   Callback interrupt level. If the value is zero, the callback function is invoked in kernel context. If the value is	more  than
		   zero,  but  less  than or equal to ten, the callback function is invoked in interrupt context at the specified interrupt level,
		   which may be used for real time applications.

		   This value must be in range of 0-10, which can be either a numeric number or a pre-defined macro (DDI_IPL_0, ... , DDI_IPL_10).

DESCRIPTION
       The ddi_periodic_add() function schedules the specified function to be periodically invoked in the nanosecond interval time.

       As with timeout(9F), the exact time interval over which the function takes effect cannot be guaranteed, but the	value  given  is  a  close
       approximation.

RETURN VALUES
       ddi_periodic_add()returns  the  non-zero  opaque  value	(ddi_periodic_t),  which  might be used for ddi_periodic_delete(9F) to specify the
       request.

CONTEXT
       The ddi_periodic_add() function may be called from user or kernel context.

EXAMPLES
       Example 1 Using ddi_periodic_add() for a periodic callback function

       In the following example, the device driver registers a periodic callback function invoked in kernel context.

	 static void
	 my_periodic_func(void *arg)
	 {
		  /*
		   * This handler is invoked periodically.
		   */
		  struct my_state *statep = (struct my_state *)arg;

		  mutex_enter(&statep->lock);
		  if (load_unbalanced(statep)) {
		      balance_tasks(statep);
		  }
		  mutex_exit(&statep->lock);
	 }

	 static void
	 start_periodic_timer(struct my_state *statep)
	 {
		  hrtime_t interval = CHECK_INTERVAL;

		  mutex_init(&statep->lock, NULL, MUTEX_DRIVER,
		      (void *)DDI_IPL_0);

		  /*
		   * Register my_callback which is invoked periodically
		   * in CHECK_INTERVAL in kernel context.
		   */
		   statep->periodic_id = ddi_periodic_add(my_periodic_func,
		       statep, interval, DDI_IPL_0);

       In the following example, the device driver registers a callback function invoked in interrupt context at level 7.

	 /*
	  * This handler is invoked periodically in interrupt context.
	  */
	  static void
	  my_periodic_int7_func(void *arg)
	  {
		   struct my_state *statep = (struct my_state *)arg;
		   mutex_enter(&statep->lock);
		   monitor_device(statep);
		   mutex_exit(&statep->lock);
	   }

	   static void
	   start_monitor_device(struct my_state *statep)
	   {
		   hrtime_t interval = MONITOR_INTERVAL;

		   mutex_init(&statep->lock, NULL, MUTEX_DRIVER,
		       (void *)DDI_IPL_7);

		   /*
		    * Register the callback function invoked periodically
		    * at interrupt level 7.
		    */
		   statep->periodic_id = ddi_periodic_add(my_periodic_int7_func,
		       statep, interval, DDI_IPL_7);
	     }

SEE ALSO
       cv_timedwait(9F), ddi_intr_get_pri(9F), ddi_periodic_delete(9F), delay(9F), drv_usectohz(9F),  qtimeout(9F),  quntimeout(9F),  timeout(9F),
       untimeout(9F)

NOTES
       A  caller  can only specify an interval in an integral multiple of 10ms. No other values are supported at this time. The interval specified
       is a lower bound on the interval on which the callback occurs.

SunOS 5.11							    2 Oct 2007						      ddi_periodic_add(9F)