time.c

是关于linux2.5.1的完全源码

		 */
		spin_lock(&i8259A_lock);
		outb(0x0c, 0x20);
		/* Ack the IRQ; AEOI will end it automatically. */
		inb(0x20);
		spin_unlock(&i8259A_lock);
	}
#endif

	do_timer(regs);
/*
 * In the SMP case we use the local APIC timer interrupt to do the
 * profiling, except when we simulate SMP mode on a uniprocessor
 * system, in that case we have to call the local interrupt handler.
 */
#ifndef CONFIG_X86_LOCAL_APIC
	if (!user_mode(regs))
		x86_do_profile(regs->rip);
#else
	if (!using_apic_timer)
		smp_local_timer_interrupt(regs);
#endif

	/*
	 * If we have an externally synchronized Linux clock, then update
	 * CMOS clock accordingly every ~11 minutes. Set_rtc_mmss() has to be
	 * called as close as possible to 500 ms before the new second starts.
	 */
	if ((time_status & STA_UNSYNC) == 0 &&
	    xtime.tv_sec > last_rtc_update + 660 &&
	    xtime.tv_usec >= 500000 - ((unsigned) tick) / 2 &&
	    xtime.tv_usec <= 500000 + ((unsigned) tick) / 2) {
		if (set_rtc_mmss(xtime.tv_sec) == 0)
			last_rtc_update = xtime.tv_sec;
		else
			last_rtc_update = xtime.tv_sec - 600; /* do it again in 60 s */
	}
}

static int use_tsc;

/*
 * This is the same as the above, except we _also_ save the current
 * Time Stamp Counter value at the time of the timer interrupt, so that
 * we later on can estimate the time of day more exactly.
 */
static void timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
{
	int count;

	/*
	 * Here we are in the timer irq handler. We just have irqs locally
	 * disabled but we don't know if the timer_bh is running on the other
	 * CPU. We need to avoid to SMP race with it. NOTE: we don' t need
	 * the irq version of write_lock because as just said we have irq
	 * locally disabled. -arca
	 */
	write_lock(&xtime_lock);
	vxtime_lock();

	if (use_tsc)
	{
		/*
		 * It is important that these two operations happen almost at
		 * the same time. We do the RDTSC stuff first, since it's
		 * faster. To avoid any inconsistencies, we need interrupts
		 * disabled locally.
		 */

		/*
		 * Interrupts are just disabled locally since the timer irq
		 * has the SA_INTERRUPT flag set. -arca
		 */
	
		/* read Pentium cycle counter */

		rdtscl(last_tsc_low);

		spin_lock(&i8253_lock);
		outb_p(0x00, 0x43);     /* latch the count ASAP */

		count = inb_p(0x40);    /* read the latched count */
		count |= inb(0x40) << 8;
		spin_unlock(&i8253_lock);

		count = ((LATCH-1) - count) * TICK_SIZE;
		delay_at_last_interrupt = (count + LATCH/2) / LATCH;
	}
 
	do_timer_interrupt(irq, NULL, regs);

	vxtime_unlock();
	write_unlock(&xtime_lock);

}

/* not static: needed by APM */
unsigned long get_cmos_time(void)
{
	unsigned int year, mon, day, hour, min, sec;
	int i;

	spin_lock(&rtc_lock); 
	/* The Linux interpretation of the CMOS clock register contents:
	 * When the Update-In-Progress (UIP) flag goes from 1 to 0, the
	 * RTC registers show the second which has precisely just started.
	 * Let's hope other operating systems interpret the RTC the same way.
	 */

	/* read RTC exactly on falling edge of update flag */
	for (i = 0 ; i < 1000000 ; i++)	/* may take up to 1 second... */
		if (CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP)
			break;
	for (i = 0 ; i < 1000000 ; i++)	/* must try at least 2.228 ms */
		if (!(CMOS_READ(RTC_FREQ_SELECT) & RTC_UIP))
			break;
	do { /* Isn't this overkill ? UIP above should guarantee consistency */
		sec = CMOS_READ(RTC_SECONDS);
		min = CMOS_READ(RTC_MINUTES);
		hour = CMOS_READ(RTC_HOURS);
		day = CMOS_READ(RTC_DAY_OF_MONTH);
		mon = CMOS_READ(RTC_MONTH);
		year = CMOS_READ(RTC_YEAR);
	} while (sec != CMOS_READ(RTC_SECONDS));
	if (!(CMOS_READ(RTC_CONTROL) & RTC_DM_BINARY) || RTC_ALWAYS_BCD)
	  {
	    BCD_TO_BIN(sec);
	    BCD_TO_BIN(min);
	    BCD_TO_BIN(hour);
	    BCD_TO_BIN(day);
	    BCD_TO_BIN(mon);
	    BCD_TO_BIN(year);
	  }
	spin_unlock(&rtc_lock); 
	if ((year += 1900) < 1970)
		year += 100;
	return mktime(year, mon, day, hour, min, sec);
}

static struct irqaction irq0  = { timer_interrupt, SA_INTERRUPT, 0, "timer", NULL, NULL};

/* ------ Calibrate the TSC ------- 
 * Return 2^32 * (1 / (TSC clocks per usec)) for do_fast_gettimeoffset().
 * Too much 64-bit arithmetic here to do this cleanly in C, and for
 * accuracy's sake we want to keep the overhead on the CTC speaker (channel 2)
 * output busy loop as low as possible. We avoid reading the CTC registers
 * directly because of the awkward 8-bit access mechanism of the 82C54
 * device.
 */

#define CALIBRATE_LATCH	(5 * LATCH)
#define CALIBRATE_TIME	(5 * 1000020/HZ)

/* Could use 64bit arithmetic on x86-64, but the code is too fragile */
static unsigned long __init calibrate_tsc(void)
{
       /* Set the Gate high, disable speaker */
	outb((inb(0x61) & ~0x02) | 0x01, 0x61);

	/*
	 * Now let's take care of CTC channel 2
	 *
	 * Set the Gate high, program CTC channel 2 for mode 0,
	 * (interrupt on terminal count mode), binary count,
	 * load 5 * LATCH count, (LSB and MSB) to begin countdown.
	 */
	outb(0xb0, 0x43);			/* binary, mode 0, LSB/MSB, Ch 2 */
	outb(CALIBRATE_LATCH & 0xff, 0x42);	/* LSB of count */
	outb(CALIBRATE_LATCH >> 8, 0x42);	/* MSB of count */

	{
		unsigned int startlow, starthigh;
		unsigned int endlow, endhigh;
		unsigned int count;

		rdtsc(startlow,starthigh);
		count = 0;
		do {
			count++;
		} while ((inb(0x61) & 0x20) == 0);
		rdtsc(endlow,endhigh);

		last_tsc_low = endlow; 

		/* Error: ECTCNEVERSET */
		if (count <= 1)
			goto bad_ctc;

		__asm__("subl %2,%0\n\t"
			"sbbl %3,%1"
			:"=a" (endlow), "=d" (endhigh)
			:"g" (startlow), "g" (starthigh),
			 "0" (endlow), "1" (endhigh));

		/* Error: ECPUTOOFAST */
		if (endhigh)
			goto bad_ctc;
		/* Error: ECPUTOOSLOW */
		if (endlow  <= CALIBRATE_TIME)
			goto bad_ctc;

		__asm__("divl %2"
			:"=a" (endlow), "=d" (endhigh)
			:"r" (endlow), "0" (0), "1" (CALIBRATE_TIME));
      	
		return endlow;
	}

	/*
	 * The CTC wasn't reliable: we got a hit on the very first read,
	 * or the CPU was so fast/slow that the quotient wouldn't fit in
	 * 32 bits..
	 */
bad_ctc:
	return 0;
}

void __init time_init(void)
{
	extern int x86_udelay_tsc;
	
	xtime.tv_sec = get_cmos_time();
	xtime.tv_usec = 0;

/*
 * If we have APM enabled or the CPU clock speed is variable
 * (CPU stops clock on HLT or slows clock to save power)
 * then the TSC timestamps may diverge by up to 1 jiffy from
 * 'real time' but nothing will break.
 * The most frequent case is that the CPU is "woken" from a halt
 * state by the timer interrupt itself, so we get 0 error. In the
 * rare cases where a driver would "wake" the CPU and request a
 * timestamp, the maximum error is < 1 jiffy. But timestamps are
 * still perfectly ordered.
 */

	if (cpu_has_tsc) {
		unsigned int tsc_quotient = calibrate_tsc();
		if (tsc_quotient) {
			fast_gettimeoffset_quotient = tsc_quotient;
			use_tsc = 1;
			/*
			 *	We could be more selective here I suspect
			 *	and just enable this for the next intel chips ?
			 */
			x86_udelay_tsc = 1;

			/* report CPU clock rate in Hz.
			 * The formula is (10^6 * 2^32) / (2^32 * 1 / (clocks/us)) =
			 * clock/second. Our precision is about 100 ppm.
			 */
			{	unsigned int eax=0, edx=1000;
				__asm__("divl %2"
		       		:"=a" (cpu_khz), "=d" (edx)
        	       		:"r" (tsc_quotient),
	                	"0" (eax), "1" (edx));
				printk("Detected %u.%03u MHz processor.\n", 
				       cpu_khz / 1000, cpu_khz % 1000);
			}
		}
	}

	setup_irq(0, &irq0);
}