illumos: manual page: delay.9f

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 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, 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, "^\007",
15 (getminor(dev) & 0xf));
16 /* wait one minute and try again */
17 delay(60 * drv_usectohz(1000000));
18 }