ktime.c

内核中关于nano计时的功能

#endif /* NTP_NANO */
		tvp->tv_sec++;
		time_maxerror += MAXFREQ / 1000;

		/*
		 * Leap second processing. If in leap-insert state at
		 * the end of the day, the system clock is set back one
		 * second; if in leap-delete state, the system clock is
		 * set ahead one second. The nano_time() routine or
		 * external clock driver will insure that reported time
		 * is always monotonic.
		 */
		switch (time_state) {

			/*
			 * No warning.
			 */
			case TIME_OK:
			if (time_status & STA_INS)
				time_state = TIME_INS;
			else if (time_status & STA_DEL)
				time_state = TIME_DEL;
			break;

			/*
			 * Insert second 23:59:60 following second
			 * 23:59:59.
			 */
			case TIME_INS:
			if (!(time_status & STA_INS))
				time_state = TIME_OK;
			else if (tvp->tv_sec % 86400 == 0) {
				tvp->tv_sec--;
				time_state = TIME_OOP;
			}
			break;

			/*
			 * Delete second 23:59:59.
			 */
			case TIME_DEL:
			if (!(time_status & STA_DEL))
				time_state = TIME_OK;
			else if ((tvp->tv_sec + 1) % 86400 == 0) {
				tvp->tv_sec++;
				time_tai--;
				time_state = TIME_WAIT;
			}
			break;

			/*
			 * Insert second in progress.
			 */
			case TIME_OOP:
			time_tai++;
			time_state = TIME_WAIT;
			break;

			/*
			 * Wait for status bits to clear.
			 */
			case TIME_WAIT:
			if (!(time_status & (STA_INS | STA_DEL)))
				time_state = TIME_OK;
		}

		/*
		 * Compute the total time adjustment for the next second
		 * in ns. The offset is reduced by a factor depending on
		 * whether the PPS signal is operating. Note that the
		 * value is in effect scaled by the clock frequency,
		 * since the adjustment is added at each tick interrupt.
		 */
		ftemp = time_offset;
#ifdef PPS_SYNC
		if (time_status & STA_PPSTIME && time_status &
		    STA_PPSSIGNAL)
			L_RSHIFT(ftemp, pps_shift);
		else
			L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#else
		L_RSHIFT(ftemp, SHIFT_PLL + time_constant);
#endif /* PPS_SYNC */
		time_adj = ftemp;
		L_SUB(time_offset, ftemp);
		L_ADD(time_adj, time_freq);
		L_ADDHI(time_adj, NANOSECOND);
#ifdef PPS_SYNC
		if (pps_valid > 0)
			pps_valid--;
		else
			time_status &= ~STA_PPSSIGNAL;
#endif /* PPS_SYNC */
	}
}

/*
 * ntp_init() - initialize variables and structures
 *
 * This routine must be called after the kernel variables hz and tick
 * are set or changed and before the next tick interrupt. In this
 * particular implementation, these values are assumed set elsewhere in
 * the kernel. The design allows the clock frequency and tick interval
 * to be changed while the system is running. So, this routine should
 * probably be integrated with the code that does that.
 */
void
ntp_init()
{
	int i;

	/*
	 * The following variable must be initialized any time the
	 * kernel variable hz is changed.
	 */
	time_tick = NANOSECOND / hz;

	/*
	 * The following variables are initialized only at startup. Only
	 * those structures not cleared by the compiler need to be
	 * initialized, and these only in the simulator. In the actual
	 * kernel, any nonzero values here will quickly evaporate.
	 */
	L_CLR(time_offset);
	L_CLR(time_freq);
	L_LINT(time_adj, NANOSECOND);
	L_CLR(time_phase);
	for (i = 0; i < NCPUS; i++)
		microset_flag[i] = 0;
#ifdef PPS_SYNC
	pps_tf[0].tv_sec = pps_tf[0].tv_nsec = 0;
	pps_tf[1].tv_sec = pps_tf[1].tv_nsec = 0;
	pps_tf[2].tv_sec = pps_tf[2].tv_nsec = 0;
	pps_fcount = 0;
	L_CLR(pps_freq);
#endif /* PPS_SYNC */ 
}

/*
 * hardupdate() - local clock update
 *
 * This routine is called by ntp_adjtime() to update the local clock
 * phase and frequency. The implementation is of an adaptive-parameter,
 * hybrid phase/frequency-lock loop (PLL/FLL). The routine computes new
 * time and frequency offset estimates for each call. If the kernel PPS
 * discipline code is configured (PPS_SYNC), the PPS signal itself
 * determines the new time offset, instead of the calling argument.
 * Presumably, calls to ntp_adjtime() occur only when the caller
 * believes the local clock is valid within some bound (+-128 ms with
 * NTP). If the caller's time is far different than the PPS time, an
 * argument will ensue, and it's not clear who will lose.
 *
 * For uncompensated quartz crystal oscillators and nominal update
 * intervals less than 256 s, operation should be in phase-lock mode,
 * where the loop is disciplined to phase. For update intervals greater
 * than 1024 s, operation should be in frequency-lock mode, where the
 * loop is disciplined to frequency. Between 256 s and 1024 s, the mode
 * is selected by the STA_MODE status bit.
 */
void
hardupdate(tvp, offset)
#ifdef NTP_NANO
	struct timespec *tvp;	/* pointer to nanosecond clock */
#else
	struct timeval *tvp;	/* pointer to microsecond clock */
#endif /* NTP_NANO */
	long offset;		/* clock offset (ns) */
{
	long mtemp;
	l_fp ftemp;

	/*
	 * Select how the phase is to be controlled and from which
	 * source. If the PPS signal is present and enabled to
	 * discipline the time, the PPS offset is used; otherwise, the
	 * argument offset is used.
	 */
	if (!(time_status & STA_PLL))
		return;
	if (!(time_status & STA_PPSTIME && time_status &
	    STA_PPSSIGNAL)) {
		if (offset > MAXPHASE)
			time_monitor = MAXPHASE;
		else if (offset < -MAXPHASE)
			time_monitor = -MAXPHASE;
		else
			time_monitor = offset;
		L_LINT(time_offset, time_monitor);
	}

	/*
	 * Select how the frequency is to be controlled and in which
	 * mode (PLL or FLL). If the PPS signal is present and enabled
	 * to discipline the frequency, the PPS frequency is used;
	 * otherwise, the argument offset is used to compute it.
	 */
	if (time_status & STA_PPSFREQ && time_status & STA_PPSSIGNAL) {
		time_reftime = tvp->tv_sec;
		return;
	}
	if (time_status & STA_FREQHOLD || time_reftime == 0)
		time_reftime = tvp->tv_sec;
	mtemp = tvp->tv_sec - time_reftime;
	L_LINT(ftemp, time_monitor);
	L_RSHIFT(ftemp, (SHIFT_PLL + 2 + time_constant) << 1);
	L_MPY(ftemp, mtemp);
	L_ADD(time_freq, ftemp);
	time_status &= ~STA_MODE;
	if (mtemp >= MINSEC && (time_status & STA_FLL || mtemp >
	    MAXSEC)) {
		L_LINT(ftemp, (time_monitor << 4) / mtemp);
		L_RSHIFT(ftemp, SHIFT_FLL + 4);
		L_ADD(time_freq, ftemp);
		time_status |= STA_MODE;
	}
	time_reftime = tvp->tv_sec;
	if (L_GINT(time_freq) > MAXFREQ)
		L_LINT(time_freq, MAXFREQ);
	else if (L_GINT(time_freq) < -MAXFREQ)
		L_LINT(time_freq, -MAXFREQ);
}

#ifdef PPS_SYNC
/*
 * hardpps() - discipline CPU clock oscillator to external PPS signal
 *
 * This routine is called at each PPS interrupt in order to discipline
 * the CPU clock oscillator to the PPS signal. There are two independent
 * first-order feedback loops, one for the phase, the other for the
 * frequency. The phase loop measures and grooms the PPS phase offset
 * and leaves it in a handy spot for the seconds overflow routine. The
 * frequency loop averages successive PPS phase differences and
 * calculates the PPS frequency offset, which is also processed by the
 * seconds overflow routine. The code requires the caller to capture the
 * time and architecture-dependent hardware counter values in
 * nanoseconds at the on-time PPS signal transition.
 *
 * Note that, on some Unix systems this routine runs at an interrupt
 * priority level higher than the timer interrupt routine hardclock().
 * Therefore, the variables used are distinct from the hardclock()
 * variables, except for the actual time and frequency variables, which
 * are determined by this routine and updated atomically.
 */
void
hardpps(tsp, nsec)
	struct timespec *tsp;	/* time at PPS */
	long nsec;		/* hardware counter at PPS */
{
	long u_sec, u_nsec, v_nsec; /* temps */
	l_fp ftemp;

	/*
	 * The signal is first processed by a range gate and frequency
	 * discriminator. The range gate rejects noise spikes outside
	 * the range +-500 us. The frequency discriminator rejects input
	 * signals with apparent frequency outside the range 1 +-500
	 * PPM. If two hits occur in the same second, we ignore the
	 * later hit; if not and a hit occurs outside the range gate,
	 * keep the later hit for later comparison, but do not process
	 * it.
	 */
	time_tick = NANOSECOND / hz;
	time_status |= STA_PPSSIGNAL | STA_PPSJITTER;
	time_status &= ~(STA_PPSWANDER | STA_PPSERROR);
	pps_valid = PPS_VALID;
	u_sec = tsp->tv_sec;
	u_nsec = tsp->tv_nsec;
	if (u_nsec >= (NANOSECOND >> 1)) {
		u_nsec -= NANOSECOND;
		u_sec++;
	}
	v_nsec = u_nsec - pps_tf[0].tv_nsec;
	if (u_sec == pps_tf[0].tv_sec && v_nsec < NANOSECOND -
	    MAXFREQ)
		return;
	pps_tf[2] = pps_tf[1];
	pps_tf[1] = pps_tf[0];
	pps_tf[0].tv_sec = u_sec;
	pps_tf[0].tv_nsec = u_nsec;

	/*
	 * Compute the difference between the current and previous
	 * counter values. If the difference exceeds 0.5 s, assume it
	 * has wrapped around, so correct 1.0 s. If the result exceeds
	 * the tick interval, the sample point has crossed a tick
	 * boundary during the last second, so correct the tick. Very
	 * intricate.
	 */
	u_nsec = nsec - pps_lastcount;
	pps_lastcount = nsec;
	if (u_nsec > (NANOSECOND >> 1))
		u_nsec -= NANOSECOND;
	else if (u_nsec < -(NANOSECOND >> 1))
		u_nsec += NANOSECOND;
	if (u_nsec > (time_tick >> 1))
		u_nsec -= time_tick;
	else if (u_nsec < -(time_tick >> 1))
		u_nsec += time_tick;
	pps_fcount += u_nsec;
	if (v_nsec > MAXFREQ || v_nsec < -MAXFREQ)
		return;
	time_status &= ~STA_PPSJITTER;

	/*
	 * A three-stage median filter is used to help denoise the PPS
	 * time. The median sample becomes the time offset estimate; the
	 * difference between the other two samples becomes the time
	 * dispersion (jitter) estimate.
	 */
	if (pps_tf[0].tv_nsec > pps_tf[1].tv_nsec) {
		if (pps_tf[1].tv_nsec > pps_tf[2].tv_nsec) {
			v_nsec = pps_tf[1].tv_nsec;	/* 0 1 2 */
			u_nsec = pps_tf[0].tv_nsec - pps_tf[2].tv_nsec;
		} else if (pps_tf[2].tv_nsec > pps_tf[0].tv_nsec) {
			v_nsec = pps_tf[0].tv_nsec;	/* 2 0 1 */
			u_nsec = pps_tf[2].tv_nsec - pps_tf[1].tv_nsec;
		} else {
			v_nsec = pps_tf[2].tv_nsec;	/* 0 2 1 */
			u_nsec = pps_tf[0].tv_nsec - pps_tf[1].tv_nsec;
		}
	} else {
		if (pps_tf[1].tv_nsec < pps_tf[2].tv_nsec) {
			v_nsec = pps_tf[1].tv_nsec;	/* 2 1 0 */
			u_nsec = pps_tf[2].tv_nsec - pps_tf[0].tv_nsec;
		} else if (pps_tf[2].tv_nsec < pps_tf[0].tv_nsec) {
			v_nsec = pps_tf[0].tv_nsec;	/* 1 0 2 */
			u_nsec = pps_tf[1].tv_nsec - pps_tf[2].tv_nsec;
		} else {
			v_nsec = pps_tf[2].tv_nsec;	/* 1 2 0 */
			u_nsec = pps_tf[1].tv_nsec - pps_tf[0].tv_nsec;
		}
	}

	/*
	 * Nominal jitter is due to PPS signal noise and interrupt
	 * latency. If it exceeds the popcorn threshold, the sample is
	 * discarded. otherwise, if so enabled, the time offset is
	 * updated. We can tolerate a modest loss of data here without
	 * much degrading time accuracy.
	 */
	if (u_nsec > (pps_jitter << PPS_POPCORN)) {
		time_status |= STA_PPSJITTER;
		pps_jitcnt++;
	} else if (time_status & STA_PPSTIME) {
		time_monitor = -v_nsec;
		L_LINT(time_offset, time_monitor);
	}
	pps_jitter += (u_nsec - pps_jitter) >> PPS_FAVG;
	u_sec = pps_tf[0].tv_sec - pps_lastsec;
	if (u_sec < (1 << pps_shift))
		return;

	/*
	 * At the end of the calibration interval the difference between
	 * the first and last counter values becomes the scaled
	 * frequency. It will later be divided by the length of the
	 * interval to determine the frequency update. If the frequency
	 * exceeds a sanity threshold, or if the actual calibration
	 * interval is not equal to the expected length, the data are
	 * discarded. We can tolerate a modest loss of data here without
	 * much degrading frequency accuracy.
	 */
	pps_calcnt++;
	v_nsec = -pps_fcount;
	pps_lastsec = pps_tf[0].tv_sec;
	pps_fcount = 0;
	u_nsec = MAXFREQ << pps_shift;
	if (v_nsec > u_nsec || v_nsec < -u_nsec || u_sec != (1 <<
	    pps_shift)) {
		time_status |= STA_PPSERROR;
		pps_errcnt++;
		return;
	}

	/*
	 * Here the raw frequency offset and wander (stability) is
	 * calculated. If the wander is less than the wander threshold
	 * for four consecutive averaging intervals, the interval is
	 * doubled; if it is greater than the threshold for four
	 * consecutive intervals, the interval is halved. The scaled
	 * frequency offset is converted to frequency offset. The
	 * stability metric is calculated as the average of recent
	 * frequency changes, but is used only for performance
	 * monitoring.
	 */
	L_LINT(ftemp, v_nsec);
	L_RSHIFT(ftemp, pps_shift);
	L_SUB(ftemp, pps_freq);
	u_nsec = L_GINT(ftemp);
	if (u_nsec > PPS_MAXWANDER) {
		L_LINT(ftemp, PPS_MAXWANDER);
		pps_intcnt--;
		time_status |= STA_PPSWANDER;
		pps_stbcnt++;
	} else if (u_nsec < -PPS_MAXWANDER) {
		L_LINT(ftemp, -PPS_MAXWANDER);
		pps_intcnt--;
		time_status |= STA_PPSWANDER;
		pps_stbcnt++;
	} else {
		pps_intcnt++;
	}
	if (pps_intcnt >= 4) {
		pps_intcnt = 4;
		if (pps_shift < pps_shiftmax) {
			pps_shift++;
			pps_intcnt = 0;
		}
	} else if (pps_intcnt <= -4) {
		pps_intcnt = -4;
		if (pps_shift > PPS_FAVG) {
			pps_shift--;
			pps_intcnt = 0;
		}
	}
	if (u_nsec < 0)
		u_nsec = -u_nsec;
	pps_stabil += (u_nsec * SCALE_PPM - pps_stabil) >> PPS_FAVG;

	/*
	 * The PPS frequency is recalculated and clamped to the maximum
	 * MAXFREQ. If enabled, the system clock frequency is updated as
	 * well.
	 */
	L_ADD(pps_freq, ftemp);
	u_nsec = L_GINT(pps_freq);
	if (u_nsec > MAXFREQ)
		L_LINT(pps_freq, MAXFREQ);
	else if (u_nsec < -MAXFREQ)
		L_LINT(pps_freq, -MAXFREQ);
	if (time_status & STA_PPSFREQ)
		time_freq = pps_freq;
}
#endif /* PPS_SYNC */