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

NAME

       delay - delay execution for a specified number of clock ticks

SYNOPSIS

       #include <sys/ddi.h>

       void delay(clock_t ticks);

INTERFACE LEVEL

       Architecture independent level 1 (DDI/DKI).

PARAMETERS

       ticks	       The number of clock cycles to delay.

DESCRIPTION

       delay() provides a mechanism for a driver to delay its execution for a given period of time. Since the speed of the clock varies among sys-
       tems, drivers should base their time values on microseconds and use drv_usectohz(9F) to convert microseconds into clock ticks.

       delay() uses timeout(9F) to schedule an internal function to be called after the specified amount of time has elapsed. delay()  then  waits
       until  the  function  is  called. Because timeout() is subject to priority inversion, drivers waiting on behalf of processes with real-time
       constraints should use cv_timedwait(9F) rather than delay().

       delay() does not busy-wait. If busy-waiting is required, use drv_usecwait(9F).

CONTEXT

       delay() can be called from user and kernel contexts.

EXAMPLES

       Example 1: delay() Example

       Before a driver I/O routine allocates buffers and stores any user data in them, it checks the status of the device (line 12). If the device
       needs  manual intervention (such as, needing to be refilled with paper), a message is displayed on the system console (line 14). The driver
       waits an allotted time (line 17) before repeating the procedure.

	1  struct  device  {	/* layout of physical device registers */
	2	   int	    control; /* physical device control word */
	3	   int	    status;  /* physical device status word */
	4	   short    xmit_char;	  /* transmit character to device */
	5  };
	6
	7
	      . . .
	9   /* get device registers  */
       10      register struct device *rp = ...
       11
       12      while (rp->status & NOPAPER) {  /* while printer is out of paper */
       13	/* display message and ring bell */
		/* on system console */
       14	   cmn_err(CE_WARN, "^07",
       15			     (getminor(dev) & 0xf));
       16	   /* wait one minute and try again */
       17	   delay(60 * drv_usectohz(1000000));
       18      }

SEE ALSO

       biodone(9F), biowait(9F), cv_timedwait(9F), ddi_in_panic(9F), drv_hztousec(9F), drv_usectohz(9F),  drv_usecwait(9F),  timeout(9F),  untime-
       out(9F)

       Writing Device Drivers

SunOS 5.10							    15 Oct 2001 							 delay(9F)