hrtime.c

来自「Linux Kernel 2.6.9 for OMAP1710」· C语言 代码 · 共 162 行

/* 
 * linux/arch/arm/mach-omap2/hrtime.c
 * 
 * High-Res Timer Implementation for OMAP2
 * HRT port on 24xx uses Timer4 to receive notification after elapsed time
 *
 * Copyright (C) 2004 Texas Instruments, Inc. 
 * 
 * This package is free software; you can redistribute it and/or modify 
 * it under the terms of the GNU General Public License version 2 as
 * published by the Free Software Foundation. 
 * 
 * THIS PACKAGE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR 
 * IMPLIED WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED 
 * WARRANTIES OF MERCHANTIBILITY AND FITNESS FOR A PARTICULAR PURPOSE. 
 */

#include <linux/config.h>
#include <linux/init.h>
#include <linux/sched.h>
#include <linux/time.h>
#include <linux/hrtime.h>
#include <linux/timex.h>
#include <linux/kernel.h>
#include <linux/interrupt.h>
#include <asm/errno.h>
#include <asm/hardware.h>
#include <asm/mach/irq.h>
#include <asm/irq.h>

int hrtimer_use = 0;

typedef struct {
	u32 tidr;		/*timer identification */
	u32 filer1;		/*reserved */
	u32 filer2;		/*reserved */
	u32 filer3;		/*reserved */
	u32 ti_ocpcfg;		/*ocp configuration */
	u32 tistat;		/*interrupt status */
	u32 tisr;		/*Timer status */
	u32 tier;		/*Timer interrupt enable */
	u32 twer;		/*Timer wake-up enable */
	u32 tclr;		/*Timer control */
	u32 tcrr;		/*Timer counter */
	u32 tldr;		/*Timer load */
	u32 ttgr;		/*Timer trigger */
	u32 twps;		/*Timer write posted status */
	u32 tmar;		/*Timer match */
	u32 tcar;		/*Timer capture */
	u32 tsicr;		/*Timer synchronization interface control */
} mputimer_regs_t;

#define HRT_TIMER_BASE      IO_ADDRESS(OMAP24XX_TIMER4_BASE)
#define HRT_TIMER_IRQ  INT_GPT4_IRQ

/*Program HRT Timer to generate interrupt at (ref_jiffies * 
 *arch_cycles_per_jiffy)+ref_cycles clock cycles from current time
 *this is called by __run_timers.this means that some Kernel Timer in Kernel
 *Timer List will expire at (ref_jiffies * arch_cycles_per_jiffy)
 * +ref_cycles from current time
 */
int schedule_hr_timer_int(unsigned ref_jiffies, int ref_cycles)
{
	int temp_cycles;
	volatile mputimer_regs_t *subhz_timer =
	    (mputimer_regs_t *) HRT_TIMER_BASE;

	BUG_ON(ref_cycles < 0);

	/*calculate the time(in terms of clock cycles) the time interval 
	   from now to the time specified by ref_jiffies+ref_cycles after 
	   ref_jiffies
	 */
	temp_cycles = (ref_jiffies - jiffies) * arch_cycles_per_jiffy +
	    ref_cycles - get_arch_cycles(jiffies);

	if (unlikely(temp_cycles <= 0))
		return -ETIME;

	/*posted mode active */
	subhz_timer->tsicr = 0x0;

	subhz_timer->tcrr = 0xffffffff - (temp_cycles - 1);

	/*enable overflow interrupt */
	subhz_timer->tier = (0x1 << 1);

	/*prescalar enable,start timer */
	subhz_timer->tclr = ((0x1 << 5) | (0x1 << 0));

	return 0;
}

/*get the elapsed timer(in terms of clock cycles) from ref_jiffies*/
int get_arch_cycles(unsigned ref_jiffies)
{
	extern unsigned long systimer_mark;
	extern unsigned long do_getmachinecycles(void);
	int ret;
	unsigned temp_jiffies;
	unsigned diff_jiffies;

	do {
		/* snapshot jiffies */
		temp_jiffies = jiffies;

		/*ensures that the opeartors placed before this are finished
		 *before starting operations placed after this
		 */
		barrier();

		/* calculate cycles since the current jiffy */
		ret = do_getmachinecycles() - systimer_mark;

		/* compensate for ref_jiffies in the past */
		if (unlikely(diff_jiffies = jiffies - ref_jiffies))
			ret += diff_jiffies * arch_cycles_per_jiffy;

		barrier();
		/* repeat if we didn't have a consistent view of the world */
	} while (unlikely(temp_jiffies != jiffies));
	return ret;
}

/*interrupt handler for HRT Timer*/
static irqreturn_t hr_timer_interrupt(int irq, void *dev_id,
				      struct pt_regs *regs)
{
	volatile mputimer_regs_t *subhz_timer =
	    (mputimer_regs_t *) HRT_TIMER_BASE;
	/*clear timer interrupt status register */
	subhz_timer->tisr = subhz_timer->tisr;
	/*stop timer */
	subhz_timer->tclr = 0;
	/*some Kernel Timer would have expired this time
	 *so process the timer list 
	 *do_hr_timer_int define as run_local_timers in include/linux/hrtime.h
	 *run_local_timers in turn calls __run_timers which process timer list
	 */
	do_hr_timer_int();
	return IRQ_HANDLED;
}

static struct irqaction hr_timer_irq = {
	.name = "high-res timer",
	.handler = hr_timer_interrupt,
	.flags = SA_INTERRUPT
};

static int hr_timer_init(void)
{
	int ret;
	volatile mputimer_regs_t *subhz_timer =
	    (mputimer_regs_t *) HRT_TIMER_BASE;
	subhz_timer->tclr = 0;
	ret = setup_irq(HRT_TIMER_IRQ, &hr_timer_irq);
	hrtimer_use = 1;
	return ret;
}

__initcall(hr_timer_init);