ktime.c

内核中关于nano计时的功能

/***********************************************************************
 *								       *
 * Copyright (c) David L. Mills 1993-2001			       *
 *								       *
 * Permission to use, copy, modify, and distribute this software and   *
 * its documentation for any purpose and without fee is hereby	       *
 * granted, provided that the above copyright notice appears in all    *
 * copies and that both the copyright notice and this permission       *
 * notice appear in supporting documentation, and that the name	       *
 * University of Delaware not be used in advertising or publicity      *
 * pertaining to distribution of the software without specific,	       *
 * written prior permission. The University of Delaware makes no       *
 * representations about the suitability this software for any	       *
 * purpose. It is provided "as is" without express or implied	       *
 * warranty.							       *
 *								       *
 **********************************************************************/

#include "kern.h"

/*
 * Generic NTP kernel interface
 *
 * These routines constitute the Network Time Protocol (NTP) interfaces
 * for user and daemon application programs. The ntp_gettime() routine
 * provides the time, maximum error (synch distance) and estimated error
 * (dispersion) to client user application programs. The ntp_adjtime()
 * routine is used by the NTP daemon to adjust the system clock to an
 * externally derived time. The time offset and related variables set by
 * this routine are used by other routines in this module to adjust the
 * phase and frequency of the clock discipline loop which controls the
 * system clock.
 *
 * When the kernel time is reckoned directly in nanoseconds (NTP_NANO
 * defined), the time at each tick interrupt is derived directly from
 * the kernel time variable. When the kernel time is reckoned in
 * microseconds, (NTP_NANO undefined), the time is derived from the
 * kernel time variable together with a variable representing the
 * leftover nanoseconds at the last tick interrupt. In either case, the
 * current nanosecond time is reckoned from these values plus an
 * interpolated value derived by the clock routines in another
 * architecture-specific module. The interpolation can use either a
 * dedicated counter or a processor cycle counter (PCC) implemented in
 * some architectures.
 *
 * Note that all routines must run at priority splclock or higher.
 */
/*
 * Phase/frequency-lock loop (PLL/FLL) definitions
 *
 * The nanosecond clock discipline uses two variable types, time
 * variables and frequency variables. Both types are represented as 64-
 * bit fixed-point quantities with the decimal point between two 32-bit
 * halves. On a 32-bit machine, each half is represented as a single
 * word and mathematical operations are done using multiple-precision
 * arithmetic. On a 64-bit machine, ordinary computer arithmetic is
 * used.
 *
 * A time variable is a signed 64-bit fixed-point number in ns and
 * fraction. It represents the remaining time offset to be amortized
 * over succeeding tick interrupts. The maximum time offset is about
 * 0.5 s and the resolution is about 2.3e-10 ns.
 *
 *			1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |s s s|			 ns				   |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |			    fraction				   |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 *
 * A frequency variable is a signed 64-bit fixed-point number in ns/s
 * and fraction. It represents the ns and fraction to be added to the
 * kernel time variable at each second. The maximum frequency offset is
 * about +-500000 ns/s and the resolution is about 2.3e-10 ns/s.
 *
 *			1 1 1 1 1 1 1 1 1 1 2 2 2 2 2 2 2 2 2 2 3 3
 *  0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |s s s s s s s s s s s s s|	          ns/s			   |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 * |			    fraction				   |
 * +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 */
/*
 * The following variables establish the state of the PLL/FLL and the
 * residual time and frequency offset of the local clock.
 */
#define SHIFT_PLL	4	/* PLL loop gain (shift) */
#define SHIFT_FLL	2	/* FLL loop gain (shift) */

int time_state = TIME_OK;	/* clock state */
int time_status = STA_UNSYNC;	/* clock status bits */
long time_tai;			/* TAI offset (s) */
long time_monitor;		/* last time offset scaled (ns) */
long time_constant;		/* poll interval (shift) (s) */
long time_precision = 1;	/* clock precision (ns) */
long time_maxerror = MAXPHASE / 1000; /* maximum error (us) */
long time_esterror = MAXPHASE / 1000; /* estimated error (us) */
long time_reftime;		/* time at last adjustment (s) */
long time_tick;			/* nanoseconds per tick (ns) */
#if !defined(NTP_NANO)
long time_nano;			/* nanoseconds past last tick */
#endif /* NTP_NANO */
l_fp time_offset;		/* time offset (ns) */
l_fp time_freq;			/* frequency offset (ns/s) */
l_fp time_adj;			/* tick adjust (ns/s) */
l_fp time_phase;		/* time phase (ns) */

#ifdef PPS_SYNC
/*
 * The following variables are used when a pulse-per-second (PPS) signal
 * is available and connected via a modem control lead. They establish
 * the engineering parameters of the clock discipline loop when
 * controlled by the PPS signal.
 */
#define PPS_FAVG	2	/* min freq avg interval (s) (shift) */
#define PPS_FAVGDEF	8	/* default freq avg int (s) (shift) */
#define PPS_FAVGMAX	15	/* max freq avg interval (s) (shift) */
#define PPS_PAVG	4	/* phase avg interval (s) (shift) */
#define PPS_VALID	120	/* PPS signal watchdog max (s) */
#define PPS_MAXWANDER	100000	/* max PPS wander (ns/s) */
#define PPS_POPCORN	2	/* popcorn spike threshold (shift) */

struct timespec pps_tf[3];	/* phase median filter */
l_fp pps_freq;			/* scaled frequency offset (ns/s) */
long pps_lastfreq;		/* last scaled freq offset (ns/s) */
long pps_fcount;		/* frequency accumulator */
long pps_jitter;		/* nominal jitter (ns) */
long pps_stabil;		/* nominal stability (scaled ns/s) */
long pps_lastcount;		/* last counter offset */
long pps_lastsec;		/* time at last calibration (s) */
int pps_valid;			/* signal watchdog counter */
int pps_shift = PPS_FAVG;	/* interval duration (s) (shift) */
int pps_shiftmax = PPS_FAVGDEF;	/* max interval duration (s) (shift) */
int pps_intcnt;			/* wander counter */

/*
 * PPS signal quality monitors
 */
long pps_calcnt;		/* calibration intervals */
long pps_jitcnt;		/* jitter limit exceeded */
long pps_stbcnt;		/* stability limit exceeded */
long pps_errcnt;		/* calibration errors */
#endif /* PPS_SYNC */
/*
 * End of phase/frequency-lock loop (PLL/FLL) definitions
 */

void hardupdate();

/*
 * ntp_gettime() - NTP user application interface
 *
 * See the timex.h header file for synopsis and API description. Note
 * that the TAI offset is returned in the ntvtimeval.tai structure
 * member. 
 */
int
ntp_gettime(tp)
	struct ntptimeval *tp;	/* pointer to argument structure */
{
	struct ntptimeval ntv;	/* temporary structure */
	struct timespec atv;	/* nanosecond time */
	int s;			/* caller priority */

	s = splclock();
	nano_time(&atv);
#ifdef NTP_NANO
	ntv.time.tv_sec = atv.tv_sec;
	ntv.time.tv_nsec = atv.tv_nsec;
#else
	if (!(time_status & STA_NANO))
		atv.tv_nsec /= 1000;
	ntv.time.tv_sec = atv.tv_sec;
	ntv.time.tv_usec = atv.tv_nsec;
#endif /* NTP_NANO */
	ntv.maxerror = time_maxerror;
	ntv.esterror = time_esterror;
	ntv.tai = time_tai;
	splx(s);
	*tp = ntv;		/* copy out the result structure */

	/*
	 * Status word error decode. If any of these conditions occur,
	 * an error is returned, instead of the status word. Most
	 * applications will care only about the fact the system clock
	 * may not be trusted, not about the details.
	 *
	 * Hardware or software error
	 */
	if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||

	/*
	 * PPS signal lost when either time or frequency synchronization
	 * requested
	 */
	    (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
	    !(time_status & STA_PPSSIGNAL)) ||

	/*
	 * PPS jitter exceeded when time synchronization requested
	 */
	    (time_status & STA_PPSTIME &&
	    time_status & STA_PPSJITTER) ||

	/*
	 * PPS wander exceeded or calibration error when frequency
	 * synchronization requested
	 */
	    (time_status & STA_PPSFREQ &&
	    time_status & (STA_PPSWANDER | STA_PPSERROR)))
		return (TIME_ERROR);
	return (time_state);
}

/*
 * ntp_adjtime() - NTP daemon application interface
 *
 * See the timex.h header file for synopsis and API description. Note
 * that the timex.constant structure member has a dual purpose to set
 * the time constant and to set the TAI offset.
 */
int
ntp_adjtime(tp)
	struct timex *tp;	/* pointer to argument structure */
{
	struct timex ntv;	/* temporary structure */
	long freq;		/* frequency ns/s) */
	int modes;		/* mode bits from structure */
	int s;			/* caller priority */

	ntv = *tp;		/* copy in the argument structure */

	/*
	 * Update selected clock variables - only the superuser can
	 * change anything. Note that there is no error checking here on
	 * the assumption the superuser should know what it is doing.
	 * Note that either the time constant or TAI offset are loaded
	 * from the ntv.constant member, depending on the mode bits. If
	 * the STA_PLL bit in the status word is cleared, the state and
	 * status words are reset to the initial values at boot.
	 */
	modes = ntv.modes;
	if (ROOT)
		return (EPERM);
	s = splclock();
	if (modes & MOD_MAXERROR)
		time_maxerror = ntv.maxerror;
	if (modes & MOD_ESTERROR)
		time_esterror = ntv.esterror;
	if (modes & MOD_STATUS) {
		if (time_status & STA_PLL && !(ntv.status & STA_PLL)) {
			time_state = TIME_OK;
			time_status = STA_UNSYNC;
#ifdef PPS_SYNC
			pps_shift = PPS_FAVG;
#endif /* PPS_SYNC */
		}
		time_status &= STA_RONLY;
		time_status |= ntv.status & ~STA_RONLY;
	}
	if (modes & MOD_TIMECONST) {
		if (ntv.constant < 0)
			time_constant = 0;
		else if (ntv.constant > MAXTC)
			time_constant = MAXTC;
		else
			time_constant = ntv.constant;
	}
	if (modes & MOD_TAI) {
		if (ntv.constant > 0)
			time_tai = ntv.constant;
	}
#ifdef PPS_SYNC
	if (modes & MOD_PPSMAX) {
		if (ntv.shift < PPS_FAVG)
			pps_shiftmax = PPS_FAVG;
		else if (ntv.shift > PPS_FAVGMAX)
			pps_shiftmax = PPS_FAVGMAX;
		else
			pps_shiftmax = ntv.shift;
	}
#endif /* PPS_SYNC */
	if (modes & MOD_NANO)
		time_status |= STA_NANO;
	if (modes & MOD_MICRO)
		time_status &= ~STA_NANO;
	if (modes & MOD_CLKB)
		time_status |= STA_CLK;
	if (modes & MOD_CLKA)
		time_status &= ~STA_CLK;
	if (modes & MOD_OFFSET) {
		if (time_status & STA_NANO)
			hardupdate(&TIMEVAR, ntv.offset);
		else
			hardupdate(&TIMEVAR, ntv.offset * 1000);
	}
	if (modes & MOD_FREQUENCY) {
		freq = ntv.freq / SCALE_PPM;
		if (freq > MAXFREQ)
			L_LINT(time_freq, MAXFREQ);
		else if (freq < -MAXFREQ)
			L_LINT(time_freq, -MAXFREQ);
		else
			L_LINT(time_freq, freq);
#ifdef PPS_SYNC
		pps_freq = time_freq;
#endif /* PPS_SYNC */
	}

	/*
	 * Retrieve all clock variables. Note that the TAI offset is
	 * returned only by ntp_gettime();
	 */
	if (time_status & STA_NANO)
		ntv.offset = time_monitor;
	else
		ntv.offset = time_monitor / 1000;
	ntv.freq = L_GINT(time_freq) * SCALE_PPM;
	ntv.maxerror = time_maxerror;
	ntv.esterror = time_esterror;
	ntv.status = time_status;
	ntv.constant = time_constant;
	if (time_status & STA_NANO)
		ntv.precision = time_precision;
	else
		ntv.precision = time_precision / 1000;
	ntv.tolerance = MAXFREQ * SCALE_PPM;
#ifdef PPS_SYNC
	ntv.shift = pps_shift;
	ntv.ppsfreq = L_GINT(pps_freq) * SCALE_PPM;
	if (time_status & STA_NANO)
		ntv.jitter = pps_jitter;
	else
		ntv.jitter = pps_jitter / 1000;
	ntv.stabil = pps_stabil;
	ntv.calcnt = pps_calcnt;
	ntv.errcnt = pps_errcnt;
	ntv.jitcnt = pps_jitcnt;
	ntv.stbcnt = pps_stbcnt;
#endif /* PPS_SYNC */
	splx(s);
	*tp = ntv;		/* copy out the result structure */

	/*
	 * Status word error decode. See comments in
	 * ntp_gettime() routine.
	 */
	if ((time_status & (STA_UNSYNC | STA_CLOCKERR)) ||
	    (time_status & (STA_PPSFREQ | STA_PPSTIME) &&
	    !(time_status & STA_PPSSIGNAL)) ||
	    (time_status & STA_PPSTIME &&
	    time_status & STA_PPSJITTER) ||
	    (time_status & STA_PPSFREQ &&
	    time_status & (STA_PPSWANDER | STA_PPSERROR)))
		return (TIME_ERROR);
	return (time_state);
}

/*
 * ntp_tick_adjust() - called every tick for precision time adjustment
 *
 * This routine is ordinarily called from the tick interrupt routine
 * hardclock(). To minimize the jitter that might result when a higher
 * priority interrupt occurs after the tick interrupt is taken and
 * before the system clock is updated, this routine (and the following
 * routine second_overflow()) should be called early in the hardclock()
 * code path. 
 */
void
ntp_tick_adjust(tvp, tick_update)
#ifdef NTP_NANO
	struct timespec *tvp;	/* pointer to nanosecond clock */
	int tick_update;	/* residual from adjtime() (ns) */
#else
	struct timeval *tvp;	/* pointer to microsecond clock */
	int tick_update;	/* residual from adjtime() (us) */
#endif /* NTP_NANO */
{
	long ltemp, time_update;

	/*
	 * Update the nanosecond and microsecond clocks. If the phase
	 * increment exceeds the tick period, update the clock phase.
	 */
#ifdef NTP_NANO
	time_update = tick_update;
	L_ADD(time_phase, time_adj);
	ltemp = L_GINT(time_phase) / hz;
	time_update += ltemp;
	L_ADDHI(time_phase, -ltemp * hz);
	tvp->tv_nsec += time_update;
#else
	time_update = tick_update;
	L_ADD(time_phase, time_adj);
	ltemp = L_GINT(time_phase) / (1000 * hz);
	time_update += ltemp;
	L_ADDHI(time_phase, -ltemp * (1000 * hz));
	tvp->tv_usec += time_update;
	time_nano = L_GINT(time_phase) / hz;
#endif /* NTP_NANO */
}

/*
 * second_overflow() - called after ntp_tick_adjust()
 *
 * This routine is ordinarily called immediately following the above
 * routine ntp_tick_adjust(). While these two routines are normally
 * combined, they are separated here only for the purposes of
 * simulation.
 */
void
second_overflow(tvp)
#ifdef NTP_NANO
	struct timespec *tvp;	/* pointer to nanosecond clock */
#else
	struct timeval *tvp;	/* pointer to microsecond clock */
#endif /* NTP_NANO */
{
	l_fp ftemp;		/* 32/64-bit temporary */

	/*
	 * On rollover of the second both the nanosecond and microsecond
	 * clocks are updated and the state machine cranked as
	 * necessary. The phase adjustment to be used for the next
	 * second is calculated and the maximum error is increased by
	 * the tolerance.
	 */
#ifdef NTP_NANO
	if (tvp->tv_nsec >= NANOSECOND) {
		tvp->tv_nsec -= NANOSECOND;
#else
	if (tvp->tv_usec >= 1000000) {
		tvp->tv_usec -= 1000000;