chutest.c

网络时间协议NTP 源码 版本v4.2.0b 该源码用于linux平台下

 * to come out at 300 ms.  Thus, peer.distance in the CHU peer structure
 * is set to 290 ms and we compute delays which are at least 10 ms long.
 * The following are 290 ms and 10 ms expressed in u_fp format
 */
#define	CHUDISTANCE	0x00004a3d
#define	CHUBASEDELAY	0x0000028f

/*
 * To compute a quality for the estimate (a pseudo delay) we add a
 * fixed 10 ms for each missing code in the minute and add to this
 * the sum of the differences between the remaining offsets and the
 * estimated sample offset.
 */
#define	CHUDELAYPENALTY	0x0000028f

/*
 * Other constant stuff
 */
#define	CHUPRECISION	(-9)		/* what the heck */
#define	CHUREFID	"CHU\0"

/*
 * Default fudge factors
 */
#define	DEFPROPDELAY	0x00624dd3	/* 0.0015 seconds, 1.5 ms */
#define	DEFFILTFUDGE	0x000d1b71	/* 0.0002 seconds, 200 us */

/*
 * Hacks to avoid excercising the multiplier.  I have no pride.
 */
#define	MULBY10(x)	(((x)<<3) + ((x)<<1))
#define	MULBY60(x)	(((x)<<6) - ((x)<<2))	/* watch overflow */
#define	MULBY24(x)	(((x)<<4) + ((x)<<3))

/*
 * Constants for use when multiplying by 0.1.  ZEROPTONE is 0.1
 * as an l_fp fraction, NZPOBITS is the number of significant bits
 * in ZEROPTONE.
 */
#define	ZEROPTONE	0x1999999a
#define	NZPOBITS	29

/*
 * The CHU table.  This gives the expected time of arrival of each
 * character after the on-time second and is computed as follows:
 * The CHU time code is sent at 300 bps.  Your average UART will
 * synchronize at the edge of the start bit and will consider the
 * character complete at the center of the first stop bit, i.e.
 * 0.031667 ms later.  Thus the expected time of each interrupt
 * is the start bit time plus 0.031667 seconds.  These times are
 * in chutable[].  To this we add such things as propagation delay
 * and delay fudge factor.
 */
#define	CHARDELAY	0x081b4e80

static u_long chutable[NCHUCHARS] = {
	0x2147ae14 + CHARDELAY,		/* 0.130 (exactly) */
	0x2ac08312 + CHARDELAY,		/* 0.167 (exactly) */
	0x34395810 + CHARDELAY,		/* 0.204 (exactly) */
	0x3db22d0e + CHARDELAY,		/* 0.241 (exactly) */
	0x472b020c + CHARDELAY,		/* 0.278 (exactly) */
	0x50a3d70a + CHARDELAY,		/* 0.315 (exactly) */
	0x5a1cac08 + CHARDELAY,		/* 0.352 (exactly) */
	0x63958106 + CHARDELAY,		/* 0.389 (exactly) */
	0x6d0e5604 + CHARDELAY,		/* 0.426 (exactly) */
	0x76872b02 + CHARDELAY,		/* 0.463 (exactly) */
};

/*
 * Keep the fudge factors separately so they can be set even
 * when no clock is configured.
 */
static l_fp propagation_delay;
static l_fp fudgefactor;
static l_fp offset_fudge;

/*
 * We keep track of the start of the year, watching for changes.
 * We also keep track of whether the year is a leap year or not.
 * All because stupid CHU doesn't include the year in the time code.
 */
static u_long yearstart;

/*
 * Imported from the timer module
 */
extern u_long current_time;
extern struct event timerqueue[];

/*
 * Time conversion tables imported from the library
 */
extern u_long ustotslo[];
extern u_long ustotsmid[];
extern u_long ustotshi[];


/*
 * init_chu - initialize internal chu driver data
 */
void
init_chu(void)
{

	/*
	 * Initialize fudge factors to default.
	 */
	propagation_delay.l_ui = 0;
	propagation_delay.l_uf = DEFPROPDELAY;
	fudgefactor.l_ui = 0;
	fudgefactor.l_uf = DEFFILTFUDGE;
	offset_fudge = propagation_delay;
	L_ADD(&offset_fudge, &fudgefactor);

	yearstart = 0;
}


void
chufilter(
	struct chucode *chuc,
	l_fp *rtime
	)
{
	register int i;
	register u_long date_ui;
	register u_long tmp;
	register u_char *code;
	int isneg;
	int imin;
	int imax;
	u_long reftime;
	l_fp off[NCHUCHARS];
	l_fp ts;
	int day, hour, minute, second;
	static u_char lastcode[NCHUCHARS];
	extern u_long calyearstart();
	extern char *mfptoa();
	void chu_process();
	extern char *prettydate();

	/*
	 * We'll skip the checks made in the kernel, but assume they've
	 * been done.  This means that all characters are BCD and
	 * the intercharacter spacing isn't unreasonable.
	 */

	/*
	 * print the code
	 */
	for (i = 0; i < NCHUCHARS; i++)
	    printf("%c%c", (chuc->codechars[i] & 0xf) + '0',
		   ((chuc->codechars[i]>>4) & 0xf) + '0');
	printf("\n");

	/*
	 * Format check.  Make sure the two halves match.
	 */
	for (i = 0; i < NCHUCHARS/2; i++)
	    if (chuc->codechars[i] != chuc->codechars[i+(NCHUCHARS/2)]) {
		    (void) printf("Bad format, halves don't match\n");
		    return;
	    }
	
	/*
	 * Break out the code into the BCD nibbles.  Only need to fiddle
	 * with the first half since both are identical.  Note the first
	 * BCD character is the low order nibble, the second the high order.
	 */
	code = lastcode;
	for (i = 0; i < NCHUCHARS/2; i++) {
		*code++ = chuc->codechars[i] & 0xf;
		*code++ = (chuc->codechars[i] >> 4) & 0xf;
	}

	/*
	 * If the first nibble isn't a 6, we're up the creek
	 */
	code = lastcode;
	if (*code++ != 6) {
		(void) printf("Bad format, no 6 at start\n");
		return;
	}

	/*
	 * Collect the day, the hour, the minute and the second.
	 */
	day = *code++;
	day = MULBY10(day) + *code++;
	day = MULBY10(day) + *code++;
	hour = *code++;
	hour = MULBY10(hour) + *code++;
	minute = *code++;
	minute = MULBY10(minute) + *code++;
	second = *code++;
	second = MULBY10(second) + *code++;

	/*
	 * Sanity check the day and time.  Note that this
	 * only occurs on the 31st through the 39th second
	 * of the minute.
	 */
	if (day < 1 || day > 366
	    || hour > 23 || minute > 59
	    || second < 31 || second > 39) {
		(void) printf("Failed date sanity check: %d %d %d %d\n",
			      day, hour, minute, second);
		return;
	}

	/*
	 * Compute seconds into the year.
	 */
	tmp = (u_long)(MULBY24((day-1)) + hour);	/* hours */
	tmp = MULBY60(tmp) + (u_long)minute;		/* minutes */
	tmp = MULBY60(tmp) + (u_long)second;		/* seconds */

	/*
	 * Now the fun begins.  We demand that the received time code
	 * be within CLOCK_WAYTOOBIG of the receive timestamp, but
	 * there is uncertainty about the year the timestamp is in.
	 * Use the current year start for the first check, this should
	 * work most of the time.
	 */
	date_ui = tmp + yearstart;
	if (date_ui < (rtime->l_ui + CLOCK_WAYTOOBIG)
	    && date_ui > (rtime->l_ui - CLOCK_WAYTOOBIG))
	    goto codeokay;	/* looks good */

	/*
	 * Trouble.  Next check is to see if the year rolled over and, if
	 * so, try again with the new year's start.
	 */
	date_ui = calyearstart(rtime->l_ui);
	if (date_ui != yearstart) {
		yearstart = date_ui;
		date_ui += tmp;
		(void) printf("time %u, code %u, difference %d\n",
			      date_ui, rtime->l_ui, (long)date_ui-(long)rtime->l_ui);
		if (date_ui < (rtime->l_ui + CLOCK_WAYTOOBIG)
		    && date_ui > (rtime->l_ui - CLOCK_WAYTOOBIG))
		    goto codeokay;	/* okay this time */
	}

	ts.l_uf = 0;
	ts.l_ui = yearstart;
	printf("yearstart %s\n", prettydate(&ts));
	printf("received %s\n", prettydate(rtime));
	ts.l_ui = date_ui;
	printf("date_ui %s\n", prettydate(&ts));

	/*
	 * Here we know the year start matches the current system
	 * time.  One remaining possibility is that the time code
	 * is in the year previous to that of the system time.  This
	 * is only worth checking if the receive timestamp is less
	 * than CLOCK_WAYTOOBIG seconds into the new year.
	 */
	if ((rtime->l_ui - yearstart) < CLOCK_WAYTOOBIG) {
		date_ui = tmp + calyearstart(yearstart - CLOCK_WAYTOOBIG);
		if ((rtime->l_ui - date_ui) < CLOCK_WAYTOOBIG)
		    goto codeokay;
	}

	/*
	 * One last possibility is that the time stamp is in the year
	 * following the year the system is in.  Try this one before
	 * giving up.
	 */
	date_ui = tmp + calyearstart(yearstart + (400*24*60*60)); /* 400 days */
	if ((date_ui - rtime->l_ui) >= CLOCK_WAYTOOBIG) {
		printf("Date hopelessly off\n");
		return;		/* hopeless, let it sync to other peers */
	}

    codeokay:
	reftime = date_ui;
	/*
	 * We've now got the integral seconds part of the time code (we hope).
	 * The fractional part comes from the table.  We next compute
	 * the offsets for each character.
	 */
	for (i = 0; i < NCHUCHARS; i++) {
		register u_long tmp2;

		off[i].l_ui = date_ui;
		off[i].l_uf = chutable[i];
		tmp = chuc->codetimes[i].tv_sec + JAN_1970;
		TVUTOTSF(chuc->codetimes[i].tv_usec, tmp2);
		M_SUB(off[i].l_ui, off[i].l_uf, tmp, tmp2);
	}

	/*
	 * Here is a *big* problem.  What one would normally
	 * do here on a machine with lots of clock bits (say
	 * a Vax or the gizmo board) is pick the most positive
	 * offset and the estimate, since this is the one that
	 * is most likely suffered the smallest interrupt delay.
	 * The trouble is that the low order clock bit on an IBM
	 * RT, which is the machine I had in mind when doing this,
	 * ticks at just under the millisecond mark.  This isn't
	 * precise enough.  What we can do to improve this is to
	 * average all 10 samples and rely on the second level
	 * filtering to pick the least delayed estimate.  Trouble
	 * is, this means we have to divide a 64 bit fixed point
	 * number by 10, a procedure which really sucks.  Oh, well.
	 * First compute the sum.
	 */
	date_ui = 0;
	tmp = 0;
	for (i = 0; i < NCHUCHARS; i++)
	    M_ADD(date_ui, tmp, off[i].l_ui, off[i].l_uf);
	if (M_ISNEG(date_ui, tmp))
	    isneg = 1;
	else
	    isneg = 0;
	
	/*
	 * Here is a multiply-by-0.1 optimization that should apply
	 * just about everywhere.  If the magnitude of the sum
	 * is less than 9 we don't have to worry about overflow
	 * out of a 64 bit product, even after rounding.
	 */
	if (date_ui < 9 || date_ui > 0xfffffff7) {
		register u_long prod_ui;
		register u_long prod_uf;

		prod_ui = prod_uf = 0;
		/*
		 * This code knows the low order bit in 0.1 is zero
		 */
		for (i = 1; i < NZPOBITS; i++) {
			M_LSHIFT(date_ui, tmp);
			if (ZEROPTONE & (1<<i))
			    M_ADD(prod_ui, prod_uf, date_ui, tmp);
		}

		/*
		 * Done, round it correctly.  Prod_ui contains the
		 * fraction.
		 */
		if (prod_uf & 0x80000000)
		    prod_ui++;
		if (isneg)
		    date_ui = 0xffffffff;
		else
		    date_ui = 0;
		tmp = prod_ui;
		/*
		 * date_ui is integral part, tmp is fraction.
		 */
	} else {
		register u_long prod_ovr;
		register u_long prod_ui;
		register u_long prod_uf;
		register u_long highbits;

		prod_ovr = prod_ui = prod_uf = 0;
		if (isneg)
		    highbits = 0xffffffff;	/* sign extend */
		else
		    highbits = 0;
		/*
		 * This code knows the low order bit in 0.1 is zero
		 */
		for (i = 1; i < NZPOBITS; i++) {
			M_LSHIFT3(highbits, date_ui, tmp);
			if (ZEROPTONE & (1<<i))
			    M_ADD3(prod_ovr, prod_uf, prod_ui,
				   highbits, date_ui, tmp);
		}

		if (prod_uf & 0x80000000)
		    M_ADDUF(prod_ovr, prod_ui, (u_long)1);
		date_ui = prod_ovr;
		tmp = prod_ui;
	}

	/*
	 * At this point we have the mean offset, with the integral
	 * part in date_ui and the fractional part in tmp.  Store
	 * it in the structure.
	 */
	/*
	 * Add in fudge factor.
	 */
	M_ADD(date_ui, tmp, offset_fudge.l_ui, offset_fudge.l_uf);

	/*
	 * Find the minimun and maximum offset
	 */
	imin = imax = 0;
	for (i = 1; i < NCHUCHARS; i++) {
		if (L_ISGEQ(&off[i], &off[imax])) {
			imax = i;
		} else if (L_ISGEQ(&off[imin], &off[i])) {
			imin = i;
		}
	}

	L_ADD(&off[imin], &offset_fudge);
	if (imin != imax)
	    L_ADD(&off[imax], &offset_fudge);
	(void) printf("mean %s, min %s, max %s\n",
		      mfptoa(date_ui, tmp, 8), lfptoa(&off[imin], 8),
		      lfptoa(&off[imax], 8));
}