PROBE_IRQ_ON

Section: Linux Kernel Functions (9)
Updated: 1997/08/14 07:53:32
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NAME

probe_irq_on, probe_irq_off - safe probing for IRQs

SYNOPSIS

#include <linux/interrupt.h>

unsigned long probe_irq_on(void)
int probe_irq_off(unsigned long irqs);

DESCRIPTION

Usage

probe_irq_on()

turns on IRQ detection. It operates by enabling all interrupts which have no handlers, while keeping the handlers for those interrupts NULL. The kernel's generic interrupt handling routine will disable these IRQs when an interrupt is received on them. probe_irq_on() adds each of these IRQ numbers to a vector which it will return. It waits approximately 100ms for any spurious interrupts that may occur, and masks these from its vector; it then returns this vector to its caller.

probe_irq_off() tests an internal list of enabled IRQs against its irqs parameter, which should be the value returned by the last probe_irq_on(). This function basically detects which IRQs have been switched off, and thus which ones have received interrupts.

Example

This explanation may seem a bit confusing, so here is an example of code the mythical FUBAR 2000 driver could use to probe for IRQs:

unsigned long irqs;
int irq;

irqs = probe_irq_on();

outb(FB2K_GIVE_ME_AN_INTERRUPT_OR_GIVE_ME_DEATH,
FB2K_CONTROL_PORT);

/* the interrupt could take a while to occur */
udelay(1000);

irq = probe_irq_off(irqs);

if (irq == 0) {
       printk("fb2k: could not detect IRQ.\n");

       printk("fb2k: Installation failed.\n");

} else if (irq == -1) {
       printk("fb2k: multiple IRQs detected.\n");

       printk("fb2k: Installation failed.\n");

} else {
       fb2k_dev->irq = irq;

       printk("fb2k: using probed IRQ %d.\n", irq);

}

RETURN VALUE

probe_irq_on() returns a bitmap of all unhandled IRQs (except those which are receiving spurious interrupts). This value should only be used as a parameter to the next call to probe_irq_off().

probe_irq_off() returns the IRQ number of whichever unhandled interrupt has occurred since the last probe_irq_on(). If no interrupts have occurred on any of the marked IRQs, 0 is returned; if interrupts have occurred on more than one of these IRQs, -1 is returned.

AVAILABILITY

Linux 1.2+. These functions are not available on m68k-based machines.

AUTHOR

Neil Moore <amethyst@maxwell.ml.org>

BUGS

As mentioned above, these functions are not available on m68k-based machines.

This manpage is way too confusing.