1. 根目录:
2. arch
3. xtensa
4. kernel
5. time.c

/*
 * arch/xtensa/kernel/time.c
 *
 * Timer and clock support.
 *
 * This file is subject to the terms and conditions of the GNU General Public
 * License.  See the file "COPYING" in the main directory of this archive
 * for more details.
 *
 * Copyright (C) 2005 Tensilica Inc.
 *
 * Chris Zankel <chris@zankel.net>
 */

#include <linux/errno.h>
#include <linux/sched.h>
#include <linux/time.h>
#include <linux/clocksource.h>
#include <linux/interrupt.h>
#include <linux/module.h>
#include <linux/init.h>
#include <linux/irq.h>
#include <linux/profile.h>
#include <linux/delay.h>

#include <asm/timex.h>
#include <asm/platform.h>

#ifdef CONFIG_XTENSA_CALIBRATE_CCOUNT
unsigned long ccount_per_jiffy;		/* per 1/HZ */
unsigned long nsec_per_ccount;		/* nsec per ccount increment */
#endif

static cycle_t ccount_read(void)
{
	return (cycle_t)get_ccount();
}

static struct clocksource ccount_clocksource = {
	.name = "ccount",
	.rating = 200,
	.read = ccount_read,
	.mask = CLOCKSOURCE_MASK(32),
};

static irqreturn_t timer_interrupt(int irq, void *dev_id);
static struct irqaction timer_irqaction = {
	.handler =	timer_interrupt,
	.flags =	IRQF_DISABLED,
	.name =		"timer",
};

void __init time_init(void)
{
#ifdef CONFIG_XTENSA_CALIBRATE_CCOUNT
	printk("Calibrating CPU frequency ");
	platform_calibrate_ccount();
	printk("%d.%02d MHz\n", (int)ccount_per_jiffy/(1000000/HZ),
			(int)(ccount_per_jiffy/(10000/HZ))%100);
#endif
	clocksource_register_hz(&ccount_clocksource, CCOUNT_PER_JIFFY * HZ);

	/* Initialize the linux timer interrupt. */

	setup_irq(LINUX_TIMER_INT, &timer_irqaction);
	set_linux_timer(get_ccount() + CCOUNT_PER_JIFFY);
}

/*
 * The timer interrupt is called HZ times per second.
 */

irqreturn_t timer_interrupt (int irq, void *dev_id)
{

	unsigned long next;

	next = get_linux_timer();

again:
	while ((signed long)(get_ccount() - next) > 0) {

		profile_tick(CPU_PROFILING);
#ifndef CONFIG_SMP
		update_process_times(user_mode(get_irq_regs()));
#endif

		xtime_update(1); /* Linux handler in kernel/time/timekeeping */

		/* Note that writing CCOMPARE clears the interrupt. */

		next += CCOUNT_PER_JIFFY;
		set_linux_timer(next);
	}

	/* Allow platform to do something useful (Wdog). */

	platform_heartbeat();

	/* Make sure we didn't miss any tick... */

	if ((signed long)(get_ccount() - next) > 0)
		goto again;

	return IRQ_HANDLED;
}

#ifndef CONFIG_GENERIC_CALIBRATE_DELAY
void __cpuinit calibrate_delay(void)
{
	loops_per_jiffy = CCOUNT_PER_JIFFY;
	printk("Calibrating delay loop (skipped)... "
	       "%lu.%02lu BogoMIPS preset\n",
	       loops_per_jiffy/(1000000/HZ),
	       (loops_per_jiffy/(10000/HZ)) % 100);
}
#endif