18  *  - To work properly, this driver needs PPS and TPV/TOFF sentences
20  *    PPS signal.
31  * This driver works slightly different from most others, as the PPS
33  * connection. This makes using both the PPS data and the serial data
35  * raw PPS stream to the core of NTPD.
41  * secondary unit is feed with the PPS samples only and can act as a PPS
71  * ?WATCH={"device":"/dev/gps0","enable":true,"json":true,"pps":true};<CRLF>
175  * + STRICT means only feed clock samples when a valid STI/PPS pair is
177  *   from PPS. Masks the serial data jitter as long PPS is available,
178  *   but can rapidly deteriorate once PPS drops out.
180  * + AUTO tries to use STI/PPS pairs if available for some time, and if
181  *   this fails for too long switches back to STI only until the PPS
202 /* Primary channel PPS avilability dance:
203  * Every good PPS sample gets us a credit of PPS_INCCOUNT points, every
204  * bad/missing PPS sample costs us a debit of PPS_DECCOUNT points. When
206  * PPS-augmented samples are fed to the core; when the account drops to
210  * PPS-augmented time stamps.
216 /* The secondary (PPS) channel uses a different strategy to avoid old
217  * PPS samples in the median filter.
288 	/* data for the secondary PPS channel */
300 	/* PPS time stamps primary + secondary channel */
301 	l_fp pps_local;	/* when we received the PPS message */
306 	int  ppscount;	/* PPS counter (primary unit) */
307 	int  ppscount2;	/* PPS counter (secondary unit) */
316 	int16_t     pps_prec;	/* PPS precision from GPSD or above */
319 	l_fp pps_fudge;		/* PPS fudge primary channel */
320 	l_fp pps_fudge2;	/* PPS fudge secondary channel */
327 	int fl_pps2  : 1;	/* valid pulse seen for PPS channel */
332 	int pf_nsec  : 1;	/* have nanosec PPS info */
347 	u_int       tc_pps_recv;/* received PPS timing info records */
886 	/* Reduce the count by one. Flush sample buffer and clear PPS  in timer_secondary()
983 		/* use TPV reference time + PPS receive time */  in eval_strict()
994 /* PPS processing for the secondary channel. GPSD provides us with full
1009 		/* PPS peer flag logic */  in eval_pps_secondary()
1048 	/* check how to handle STI+PPS: Can PPS be used to augment STI  in eval_auto()
1050 	 * temporary missing PPS signal, or do we feed on STI time  in eval_auto()
1061 				"%s: expect valid PPS from now",  in eval_auto()
1501 	/* With the 3.9 GPSD protocol, '*_musec' vanished from the PPS  in process_version()
1530 	 * request PPS (and TOFF) transmission.  in process_version()
1534 		 up->device, (up->pf_toff ? ",\"pps\":true" : ""));  in process_version()
1616 	 * data presion instead. (Note: The PPS branch has a different  in process_tpv()
1645 	 * if we're explicitely requested to ignore PPS data.  in process_pps()
1671 	/* Try to read the precision field from the PPS record. If it's  in process_pps()
1694 	DPRINTF(2, ("%s: PPS record processed,"  in process_pps()
1705 	DPRINTF(1, ("%s: PPS record processing FAILED\n",  in process_pps()
1787 	else if (!strcmp("PPS", clsid))  in gpsd_parse()
1799 	/* if possible, feed the PPS side channel */  in gpsd_parse()
1804 	/* check PPS vs. STI receive times:  in gpsd_parse()
1805 	 * If STI is before PPS, then clearly the STI is too old. If PPS  in gpsd_parse()
1806 	 * is before STI by more than one second, then PPS is too old.  in gpsd_parse()
1814 			up->fl_pps = 0; /* pps too old */  in gpsd_parse()