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Unix/Linux 网络时间协议版本3 Network Time Protocol Version 3 (NTP) distribution for Unix systems

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          28 Mar 97 12:06 GMT
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	Fri, 28 Mar 1997 14:06:36 +0200 (SAT)
From: John Hay <[e-mail]>
Message-Id: <[e-mail]>
Subject: xntpd TIOCDCDTIMESTAMP support and NMEA improvements
To: [e-mail]
Date: Fri, 28 Mar 1997 14:06:36 +0200 (SAT)
Cc: Harlan Stenn <[e-mail]>
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Hi Dave,

Here is my revised patches from the ones I sent you previously. The only
real change is that I don't have the #ifdef MOTOROLA_NMEAGPS any more.
After thinking about it, I realized that all other GPS's will ignore it,
so I just left it in.

The first two patches change xntpd/ntp_refclock.c and html/ldisc.html.
This is the support for the FreeBSD TIOCDCDTIMESTAMP ioctl. It will
only be compiled in if that ioctl exists, so it should not interfere
on other platforms. I documented it in ldisc.html. I'm not sure if
that is the best place.

The last three patches is some improvements to the NMEA code and the
start of a doc (driver20.html) for it. The files affected is: xntpd/
refclock_nmea.c, html/refclock.html and the new driver20.html.

Please feel free to fix the english especially in the docs. English
is not my native language. Also if you would like to do things
differently or have suggestions on things that I can do better, I'd
like to hear them.

Thanks.

PS. Harlan this is cc'ed to you because you asked if I can get rid of
the #ifdef MOTOROLA_NMEAGPS.

John
-- 
John Hay -- [e-mail]


*** xntpd/ntp_refclock.c.orig	Thu Jan 30 09:27:12 1997
--- xntpd/ntp_refclock.c	Fri Mar 28 12:13:49 1997
***************
*** 685,690 ****
--- 685,693 ----
  	int i;
  	l_fp trtmp, tstmp;
  	char c;
+ #ifdef TIOCDCDTIMESTAMP
+ 	struct timeval dcd_time;
+ #endif
  
  	/*
  	 * Check for the presence of a timestamp left by the tty_clock
***************
*** 696,701 ****
--- 699,727 ----
  	dpt = (char *)&rbufp->recv_space;
  	dpend = dpt + rbufp->recv_length;
  	trtmp = rbufp->recv_time;
+ 
+ #ifdef TIOCDCDTIMESTAMP
+ 	if(ioctl(rbufp->fd, TIOCDCDTIMESTAMP, &dcd_time) != -1) {
+ 		TVTOTS(&dcd_time, &tstmp);
+ 		tstmp.l_ui += JAN_1970;
+ 		L_SUB(&trtmp, &tstmp);
+ 		if (trtmp.l_ui == 0) {
+ #ifdef DEBUG
+ 				if (debug) {
+ 					printf(
+ 				    "refclock_gtlin: fd %d DCDTIMESTAMP %s",
+ 					    rbufp->fd,
+ 					    lfptoa(&tstmp, 6));
+ 					printf(" sigio %s\n",
+ 					    lfptoa(&trtmp, 6));
+ 				}
+ #endif
+ 			trtmp = tstmp;
+ 		} else
+ 			trtmp = rbufp->recv_time;
+ 	}
+ 
+ #else /* TIOCDCDTIMESTAMP */
  	if (dpend >= dpt + 8) {
  		if (buftvtots(dpend - 8, &tstmp)) {
  			L_SUB(&trtmp, &tstmp);
***************
*** 718,723 ****
--- 744,750 ----
  				trtmp = rbufp->recv_time;
  		}
  	}
+ #endif /* TIOCDCDTIMESTAMP */
  
  	/*
  	 * Edit timecode to remove control chars. Don't monkey with the
*** html/ldisc.html.orig	Thu Oct 10 19:20:41 1996
--- html/ldisc.html	Fri Mar 28 12:13:50 1997
***************
*** 142,145 ****
--- 142,161 ----
  the current values of the timestamp and counter are returned in the
  <code>ppsclockev</code> structure.
  
+ <p><h4>TIOCDCDTIMESTAMP timestamping</h4>
+ 
+ <p>On FreeBSD 2.2 and later systems the TIOCDCDTIMESTAMP ioctl is used
+ to read the timestamp when the DCD serial go active. To use this the
+ PPS signal must be tied to the serial port DCD signal through the
+ appropriate level converters and pulse stretch circuitry if necessary.
+ This enhances the accuracy of the driver to a few microseconds. Using
+ FreeBSD 2.2 the measured delay between activation of the PPS signal and
+ the time the timestamp is made on a 66MHz 486DX2 is 19us and on a
+ 100MHz Pentium is 6us. The driver does NOT compensate for this.
+ 
+ <p>The TIOCDCDTIMESTAMP timestamping ioctl() is used automatically
+ on FreeBSD systems if available. It is integrated into the
+ refclock_gtlin() function so any driver using it will benefit from
+ the enhanced accuracy.
+ 
  <hr><address>David L. Mills ([e-mail])</address></body></html>
*** xntpd/refclock_nmea.c.orig	Tue Feb  4 03:01:37 1997
--- xntpd/refclock_nmea.c	Fri Mar 28 12:36:47 1997
***************
*** 36,41 ****
--- 36,42 ----
  #define	DEVICE		"/dev/gps%d"	/* name of radio device */
  #define	SPEED232	B4800	/* uart speed (4800 bps) */
  #define	PRECISION	(-9)	/* precision assumed (about 2 ms) */
+ #define	DCD_PRECISION	(-20)	/* precision assumed (about 1 us) */
  #define	REFID		"GPS\0"	/* reference id */
  #define	DESCRIPTION	"NMEA GPS Clock" /* who we are */
  
***************
*** 69,74 ****
--- 70,76 ----
   */
  struct nmeaunit {
  	int	pollcnt;	/* poll message counter */
+ 	int	polled;		/* Hand in a sample? */
  	l_fp	tstamp;		/* timestamp of last poll */
  };
  
***************
*** 80,85 ****
--- 82,88 ----
  static	void	nmea_receive	P((struct recvbuf *));
  static	void	nmea_poll	P((int, struct peer *));
  static	void	gps_send	P((int, char *, struct peer *));
+ static	char	*field_parse	P((char *, int));
  
  /*
   * Transfer vector
***************
*** 142,152 ****
  	/*
  	 * Initialize miscellaneous variables
  	 */
! 	peer->precision = PRECISION;
  	pp->clockdesc = DESCRIPTION;
  	memcpy((char *)&pp->refid, REFID, 4);
  	up->pollcnt = 2;
  	gps_send(pp->io.fd,"$PMOTG,RMC,0000*1D\r\n", peer);
  	return (1);
  }
  
--- 145,156 ----
  	/*
  	 * Initialize miscellaneous variables
  	 */
! 	peer->precision = DCD_PRECISION;
  	pp->clockdesc = DESCRIPTION;
  	memcpy((char *)&pp->refid, REFID, 4);
  	up->pollcnt = 2;
  	gps_send(pp->io.fd,"$PMOTG,RMC,0000*1D\r\n", peer);
+ 
  	return (1);
  }
  
***************
*** 182,188 ****
  	int i;
  	char *cp, *dp;
  	int cmdtype;
- 	char *field_parse();
  
  	/*
  	 * Initialize pointers and read the timecode and timestamp
--- 186,191 ----
***************
*** 199,212 ****
  		return;
  
  	/*
! 	 * We get a buffer and timestamp for each <cr>; however, we use
! 	 * the timestamp of "now" since this may be a broadcast instead
! 	 * of a poll.  This needs to be checked empirically
  	 */
! 	get_systime(&up->tstamp);		/* HACK */
! 	pp->lastrec = up->tstamp;
  	up->pollcnt = 2;
- 	record_clock_stats(&peer->srcadr, pp->lastcode);
  #ifdef DEBUG
  	if (debug)
          	printf("nmea: timecode %d %s\n", pp->lencode,
--- 202,211 ----
  		return;
  
  	/*
! 	 * We get a buffer and timestamp for each <cr>.
  	 */
! 	pp->lastrec = up->tstamp = trtmp;
  	up->pollcnt = 2;
  #ifdef DEBUG
  	if (debug)
          	printf("nmea: timecode %d %s\n", pp->lencode,
***************
*** 263,268 ****
--- 262,276 ----
  
  	}
  
+ 	/*
+ 	 * Only go on if we had been polled.
+ 	 */
+ 	if(!up->polled)
+ 		return;
+ 	up->polled = 0;
+ 
+ 	record_clock_stats(&peer->srcadr, pp->lastcode);
+ 
  	dp = field_parse(cp,9);
  	/*
  	 * Convert date and check values.
***************
*** 354,359 ****
--- 362,368 ----
  	else
  		up->pollcnt--;
  	pp->polls++;
+ 	up->polled = 1;
  
  	/*
  	 * usually nmea_receive can get a timestamp every second
*** html/refclock.html.org	Thu Oct 10 19:20:45 1996
--- html/refclock.html	Fri Mar 28 12:56:41 1997
***************
*** 69,75 ****
  (<code>ACTS</code>)
  <br><a href="driver19.html">Type 19</a> Heath WWV/WWVH Receiver
  (<code>HEATH</code>)
! <br>Type 20 Generic NMEA GPS Receiver (<code>NMEA</code>)
  <br>Type 21 TrueTime GPS-VME Interface (HP only) (<code>GPSVME</code>)
  <br><a href="driver22.html">Type 22</a> PPS Clock Discipline
  (<code>ATOM</code>)
--- 69,75 ----
  (<code>ACTS</code>)
  <br><a href="driver19.html">Type 19</a> Heath WWV/WWVH Receiver
  (<code>HEATH</code>)
! <br><a href="driver20.html">Type 20</a> Generic NMEA GPS Receiver (<code>NMEA</code>)
  <br>Type 21 TrueTime GPS-VME Interface (HP only) (<code>GPSVME</code>)
  <br><a href="driver22.html">Type 22</a> PPS Clock Discipline
  (<code>ATOM</code>)
*** /dev/null	Fri Mar 28 12:16:36 1997
--- html/driver20.html	Fri Mar 28 13:03:52 1997
***************
*** 0 ****
--- 1,106 ----
+ <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML Strict//EN">
+ <html><head><title>
+ Generic NMEA GPS Receiver
+ </title></head><body><h3>
+ Generic NMEA GPS Receiver
+ </h3><hr>
+ 
+ <p><h4>Synopsis</h4>
+ 
+ <p>Address: 127.127.20.<var>u</var>
+ <br>Reference ID: GPS
+ <br>Driver ID: GPS_NMEA
+ <br>Serial Port: <code>/dev/gps<var>u</var></code>; 4800 baud, 8-bits,
+ no parity
+ <br>Features: <code>tty_clk</code>
+ 
+ <p><h4>Description</h4>
+ 
+ <p>This driver supports GPS's with the $GPRMC NMEA output string. The
+ driver expect the GPS to be set up to transmit a $GPRMC message every
+ second.
+ 
+ <p>The accuracy depend on the GPS used. Inexpesive GPS models are
+ available with a claimed PPS signal accuracy of 1us or better relative
+ to the broadcast signal. However, in most cases the actual accuracy is
+ limited by the precision of the timecode and the latencies of the
+ serial interface and operating system.
+ 
+ <p>The $GPRMC message that the GPS transmits look like this:
+ <pre>
+ $GPRMC,POS_UTC,POS_STAT,LAT,LAT_REF,LON,LON_REF,SPD,HDG,DATE,MAG_VAR,MAG_REF*CC&lt;cr&gt;&lt;lf&gt;
+ 
+   POS_UTC  - UTC of position. Hours, minutes and seconds. (hhmmss)
+   POS_STAT - Position status. (A = Data valid, V = Data invalid)
+   LAT      - Latitude (llll.ll)
+   LAT_REF  - Latitude direction. (N = North, S = South)
+   LON      - Longitude (yyyyy.yy)
+   LON_REF  - Longitude direction (E = East, W = West)
+   SPD      - Speed over ground. (knots) (x.x)
+   HDG      - Heading/track made good (degrees True) (x.x)
+   DATE     - Date (ddmmyy)
+   MAG_VAR  - Magnetic variation (degrees) (x.x)
+   MAG_REF  - Magnetic variation (E = East, W = West)
+   CC       - Checksum (optional)
+   &lt;cr&gt;&lt;lf&gt; - Sentence terminator.
+ </pre>
+ 
+ <p>The driver will send a "$PMOTG,RMC,0000*1D&lt;cr&gt;&lt;lf&gt;"
+ message each time a $GPRMC string is needed. This is not needed on most
+ GPS receivers because they automatically send the $GPRMC string every
+ second and will only work on GPS receivers that understand the $PMOTG
+ string. Others will just ignore it.
+ 
+ <p><h4>Setting up the Garmin GPS-25XL</h4>
+ 
+ <p>Switch off all output with by sending it the following string.
+ <pre>"$PGRMO,,2&lt;cr&gt;&lt;lf&gt;"</pre>
+ Now switch only $GPRMC on by sending it the following string.
+ <pre>"$PGRMO,GPRMC,1&lt;cr&gt;&lt;lf&gt;"</pre>
+ 
+ <p>On some systems the PPS signal isn't switched on by default. It can
+ be switched on by sending the following string.
+ <pre>"$PGRMC,,,,,,,,,,,,2&lt;cr&gt;&lt;lf&gt;"</pre>
+ 
+ <p><h4>Monitor Data</h4>
+ 
+ <p>The $GPRMC string that is used is written to the clockstats file.
+ 
+ <p><h4>Fudge Factors</h4>
+ 
+ <dl>
+ 
+ <dt><code>time1 <var>time</var></code>
+ <dd>Specifies the time offset calibration factor, in seconds and
+ fraction, with default 0.0.
+ 
+ <p><dt><code>time2 <var>time</var></code>
+ <dd>Not used by this driver.
+ 
+ <p><dt><code>stratum <var>number</var></code>
+ <dd>Specifies the driver stratum, in decimal from 0 to 15, with default
+ 0.
+ 
+ <p><dt><code>refid <var>string</var></code>
+ <dd>Specifies the driver reference identifier, an ASCII string from one
+ to four characters, with default <code>GPS</code>.
+ 
+ <p><dt><code>flag1 0 | 1</code>
+ <dd>Not used by this driver.
+ 
+ <p><dt><code>flag2 0 | 1</code>
+ <dd>Not used by this driver.
+ 
+ <p><dt><code>flag3 0 | 1</code>
+ <dd>Not used by this driver.
+ 
+ <p><dt><code>flag4 0 | 1</code>
+ <dd>Not used by this driver.
+ 
+ <p>Additional Information
+ 
+ <p><a href="refclock.html"> Reference Clock Drivers</a>
+ 
+ </dl>
+ 
+ <hr><address>David L. Mills ([e-mail])</address></body></html>