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  exe-
     cution  for  a  given period of time. Since the speed of the
     clock varies among systems, 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, need-
     ing  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, "^\007",
     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), untimeout(9F)

     Writing Device Drivers