drv_usecwait(9f) [xfree86 man page]
drv_usecwait(9F) Kernel Functions for Drivers drv_usecwait(9F) NAME
drv_usecwait - busy-wait for specified interval SYNOPSIS
#include <sys/types.h> #include <sys/ddi.h> void drv_usecwait(clock_t microsecs); INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI). PARAMETERS
microsecs The number of microseconds to busy-wait. DESCRIPTION
drv_usecwait() gives drivers a means of busy-waiting for a specified microsecond count. The amount of time spent busy-waiting may be greater than the microsecond count but will minimally be the number of microseconds specified. delay(9F) can be used by a driver to delay for a specified number of system ticks, but it has two limitations. First, the granularity of the wait time is limited to one clock tick, which may be more time than is needed for the delay. Second, delay(9F) may only be invoked from user context and hence cannot be used at interrupt time or system initialization. Often, drivers need to delay for only a few microseconds, waiting for a write to a device register to be picked up by the device. In this case, even in user context, delay(9F) produces too long a wait period. CONTEXT
drv_usecwait() can be called from user or interrupt context. SEE ALSO
delay(9F), timeout(9F), untimeout(9F) Writing Device Drivers NOTES
The driver wastes processor time by making this call since drv_usecwait() does not block but simply busy-waits. The driver should only make calls to drv_usecwait() as needed, and only for as much time as needed. drv_usecwait() does not mask out interrupts. SunOS 5.10 12 Nov 1992 drv_usecwait(9F)
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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)