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

delay - delay execution for a specified number of clock ticks

#include <sys/ddi.h>
void delay(clock_t ticks);

Architecture independent level 1 (DDI/DKI).

The number of clock cycles to delay.

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 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).

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

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  };
 9      /* get device registers */
10      register struct device *rp = ...
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      }

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

October 15, 2001 OmniOS