2 * refclock_irig - audio IRIG-B/E demodulator/decoder
8 #if defined(REFCLOCK) && defined(CLOCK_IRIG)
12 #include "ntp_refclock.h"
13 #include "ntp_calendar.h"
14 #include "ntp_stdlib.h"
19 #ifdef HAVE_SYS_IOCTL_H
20 #include <sys/ioctl.h>
21 #endif /* HAVE_SYS_IOCTL_H */
26 * Audio IRIG-B/E demodulator/decoder
28 * This driver synchronizes the computer time using data encoded in
29 * IRIG-B/E signals commonly produced by GPS receivers and other timing
30 * devices. The IRIG signal is an amplitude-modulated carrier with
31 * pulse-width modulated data bits. For IRIG-B, the carrier frequency is
32 * 1000 Hz and bit rate 100 b/s; for IRIG-E, the carrier frequenchy is
33 * 100 Hz and bit rate 10 b/s. The driver automatically recognizes which
36 * The driver requires an audio codec or sound card with sampling rate 8
37 * kHz and mu-law companding. This is the same standard as used by the
38 * telephone industry and is supported by most hardware and operating
39 * systems, including Solaris, SunOS, FreeBSD, NetBSD and Linux. In this
40 * implementation, only one audio driver and codec can be supported on a
43 * The program processes 8000-Hz mu-law companded samples using separate
44 * signal filters for IRIG-B and IRIG-E, a comb filter, envelope
45 * detector and automatic threshold corrector. Cycle crossings relative
46 * to the corrected slice level determine the width of each pulse and
47 * its value - zero, one or position identifier.
49 * The data encode 20 BCD digits which determine the second, minute,
50 * hour and day of the year and sometimes the year and synchronization
51 * condition. The comb filter exponentially averages the corresponding
52 * samples of successive baud intervals in order to reliably identify
53 * the reference carrier cycle. A type-II phase-lock loop (PLL) performs
54 * additional integration and interpolation to accurately determine the
55 * zero crossing of that cycle, which determines the reference
56 * timestamp. A pulse-width discriminator demodulates the data pulses,
57 * which are then encoded as the BCD digits of the timecode.
59 * The timecode and reference timestamp are updated once each second
60 * with IRIG-B (ten seconds with IRIG-E) and local clock offset samples
61 * saved for later processing. At poll intervals of 64 s, the saved
62 * samples are processed by a trimmed-mean filter and used to update the
65 * An automatic gain control feature provides protection against
66 * overdriven or underdriven input signal amplitudes. It is designed to
67 * maintain adequate demodulator signal amplitude while avoiding
68 * occasional noise spikes. In order to assure reliable capture, the
69 * decompanded input signal amplitude must be greater than 100 units and
70 * the codec sample frequency error less than 250 PPM (.025 percent).
74 * The timecode format used for debugging and data recording includes
75 * data helpful in diagnosing problems with the IRIG signal and codec
76 * connections. The driver produces one line for each timecode in the
79 * 00 00 98 23 19:26:52 2782 143 0.694 10 0.3 66.5 3094572411.00027
81 * If clockstats is enabled, the most recent line is written to the
82 * clockstats file every 64 s. If verbose recording is enabled (fudge
83 * flag 4) each line is written as generated.
85 * The first field containes the error flags in hex, where the hex bits
86 * are interpreted as below. This is followed by the year of century,
87 * day of year and time of day. Note that the time of day is for the
88 * previous minute, not the current time. The status indicator and year
89 * are not produced by some IRIG devices and appear as zeros. Following
90 * these fields are the carrier amplitude (0-3000), codec gain (0-255),
91 * modulation index (0-1), time constant (4-10), carrier phase error
92 * +-.5) and carrier frequency error (PPM). The last field is the on-
93 * time timestamp in NTP format.
95 * The error flags are defined as follows in hex:
97 * x01 Low signal. The carrier amplitude is less than 100 units. This
98 * is usually the result of no signal or wrong input port.
99 * x02 Frequency error. The codec frequency error is greater than 250
100 * PPM. This may be due to wrong signal format or (rarely)
102 * x04 Modulation error. The IRIG modulation index is less than 0.5.
103 * This is usually the result of an overdriven codec, wrong signal
104 * format or wrong input port.
105 * x08 Frame synch error. The decoder frame does not match the IRIG
106 * frame. This is usually the result of an overdriven codec, wrong
107 * signal format or noisy IRIG signal. It may also be the result of
108 * an IRIG signature check which indicates a failure of the IRIG
109 * signal synchronization source.
110 * x10 Data bit error. The data bit length is out of tolerance. This is
111 * usually the result of an overdriven codec, wrong signal format
112 * or noisy IRIG signal.
113 * x20 Seconds numbering discrepancy. The decoder second does not match
114 * the IRIG second. This is usually the result of an overdriven
115 * codec, wrong signal format or noisy IRIG signal.
116 * x40 Codec error (overrun). The machine is not fast enough to keep up
118 * x80 Device status error (Spectracom).
121 * Once upon a time, an UltrSPARC 30 and Solaris 2.7 kept the clock
122 * within a few tens of microseconds relative to the IRIG-B signal.
123 * Accuracy with IRIG-E was about ten times worse. Unfortunately, Sun
124 * broke the 2.7 audio driver in 2.8, which has a 10-ms sawtooth
127 * Unlike other drivers, which can have multiple instantiations, this
128 * one supports only one. It does not seem likely that more than one
129 * audio codec would be useful in a single machine. More than one would
130 * probably chew up too much CPU time anyway.
134 * Fudge flag4 causes the dubugging output described above to be
135 * recorded in the clockstats file. Fudge flag2 selects the audio input
136 * port, where 0 is the mike port (default) and 1 is the line-in port.
137 * It does not seem useful to select the compact disc player port. Fudge
138 * flag3 enables audio monitoring of the input signal. For this purpose,
139 * the monitor gain is set t a default value. Fudgetime2 is used as a
140 * frequency vernier for broken codec sample frequency.
144 * CEVNT_BADTIME invalid date or time
145 * CEVNT_TIMEOUT no IRIG data since last poll
148 * Interface definitions
150 #define DEVICE_AUDIO "/dev/audio" /* audio device name */
151 #define PRECISION (-17) /* precision assumed (about 10 us) */
152 #define REFID "IRIG" /* reference ID */
153 #define DESCRIPTION "Generic IRIG Audio Driver" /* WRU */
154 #define AUDIO_BUFSIZ 320 /* audio buffer size (40 ms) */
155 #define SECOND 8000 /* nominal sample rate (Hz) */
156 #define BAUD 80 /* samples per baud interval */
157 #define OFFSET 128 /* companded sample offset */
158 #define SIZE 256 /* decompanding table size */
159 #define CYCLE 8 /* samples per bit */
160 #define SUBFLD 10 /* bits per frame */
161 #define FIELD 100 /* bits per second */
162 #define MINTC 2 /* min PLL time constant */
163 #define MAXTC 10 /* max PLL time constant max */
164 #define MAXAMP 3000. /* maximum signal amplitude */
165 #define MINAMP 2000. /* minimum signal amplitude */
166 #define DRPOUT 100. /* dropout signal amplitude */
167 #define MODMIN 0.5 /* minimum modulation index */
168 #define MAXFREQ (250e-6 * SECOND) /* freq tolerance (.025%) */
171 * The on-time synchronization point is the positive-going zero crossing
172 * of the first cycle of the second. The IIR baseband filter phase delay
173 * is 1.03 ms for IRIG-B and 3.47 ms for IRIG-E. The fudge value 2.68 ms
174 * due to the codec and other causes was determined by calibrating to a
175 * PPS signal from a GPS receiver.
177 * The results with a 2.4-GHz P4 running FreeBSD 6.1 are generally
178 * within .02 ms short-term with .02 ms jitter. The processor load due
179 * to the driver is 0.51 percent.
181 #define IRIG_B ((1.03 + 2.68) / 1000) /* IRIG-B system delay (s) */
182 #define IRIG_E ((3.47 + 2.68) / 1000) /* IRIG-E system delay (s) */
185 * Data bit definitions
187 #define BIT0 0 /* zero */
188 #define BIT1 1 /* one */
189 #define BITP 2 /* position identifier */
194 #define IRIG_ERR_AMP 0x01 /* low carrier amplitude */
195 #define IRIG_ERR_FREQ 0x02 /* frequency tolerance exceeded */
196 #define IRIG_ERR_MOD 0x04 /* low modulation index */
197 #define IRIG_ERR_SYNCH 0x08 /* frame synch error */
198 #define IRIG_ERR_DECODE 0x10 /* frame decoding error */
199 #define IRIG_ERR_CHECK 0x20 /* second numbering discrepancy */
200 #define IRIG_ERR_ERROR 0x40 /* codec error (overrun) */
201 #define IRIG_ERR_SIGERR 0x80 /* IRIG status error (Spectracom) */
203 static char hexchar[] = "0123456789abcdef";
206 * IRIG unit control structure
209 u_char timecode[2 * SUBFLD + 1]; /* timecode string */
210 l_fp timestamp; /* audio sample timestamp */
211 l_fp tick; /* audio sample increment */
212 l_fp refstamp; /* reference timestamp */
213 l_fp chrstamp; /* baud timestamp */
214 l_fp prvstamp; /* previous baud timestamp */
215 double integ[BAUD]; /* baud integrator */
216 double phase, freq; /* logical clock phase and frequency */
217 double zxing; /* phase detector integrator */
218 double yxing; /* cycle phase */
219 double exing; /* envelope phase */
220 double modndx; /* modulation index */
221 double irig_b; /* IRIG-B signal amplitude */
222 double irig_e; /* IRIG-E signal amplitude */
223 int errflg; /* error flags */
225 * Audio codec variables
227 double comp[SIZE]; /* decompanding table */
228 double signal; /* peak signal for AGC */
229 int port; /* codec port */
230 int gain; /* codec gain */
231 int mongain; /* codec monitor gain */
232 int seccnt; /* second interval counter */
237 double bpf[9]; /* IRIG-B filter shift register */
238 double lpf[5]; /* IRIG-E filter shift register */
239 double envmin, envmax; /* envelope min and max */
240 double slice; /* envelope slice level */
241 double intmin, intmax; /* integrated envelope min and max */
242 double maxsignal; /* integrated peak amplitude */
243 double noise; /* integrated noise amplitude */
244 double lastenv[CYCLE]; /* last cycle amplitudes */
245 double lastint[CYCLE]; /* last integrated cycle amplitudes */
246 double lastsig; /* last carrier sample */
247 double fdelay; /* filter delay */
248 int decim; /* sample decimation factor */
249 int envphase; /* envelope phase */
250 int envptr; /* envelope phase pointer */
251 int envsw; /* envelope state */
252 int envxing; /* envelope slice crossing */
253 int tc; /* time constant */
254 int tcount; /* time constant counter */
255 int badcnt; /* decimation interval counter */
260 int pulse; /* cycle counter */
261 int cycles; /* carrier cycles */
262 int dcycles; /* data cycles */
263 int lastbit; /* last code element */
264 int second; /* previous second */
265 int bitcnt; /* bit count in frame */
266 int frmcnt; /* bit count in second */
267 int xptr; /* timecode pointer */
268 int bits; /* demodulated bits */
272 * Function prototypes
274 static int irig_start (int, struct peer *);
275 static void irig_shutdown (int, struct peer *);
276 static void irig_receive (struct recvbuf *);
277 static void irig_poll (int, struct peer *);
280 * More function prototypes
282 static void irig_base (struct peer *, double);
283 static void irig_rf (struct peer *, double);
284 static void irig_baud (struct peer *, int);
285 static void irig_decode (struct peer *, int);
286 static void irig_gain (struct peer *);
291 struct refclock refclock_irig = {
292 irig_start, /* start up driver */
293 irig_shutdown, /* shut down driver */
294 irig_poll, /* transmit poll message */
295 noentry, /* not used (old irig_control) */
296 noentry, /* initialize driver (not used) */
297 noentry, /* not used (old irig_buginfo) */
298 NOFLAGS /* not used */
303 * irig_start - open the devices and initialize data for processing
307 int unit, /* instance number (used for PCM) */
308 struct peer *peer /* peer structure pointer */
311 struct refclockproc *pp;
317 int fd; /* file descriptor */
319 double step; /* codec adjustment */
324 fd = audio_init(DEVICE_AUDIO, AUDIO_BUFSIZ, unit);
333 * Allocate and initialize unit structure
335 up = emalloc_zero(sizeof(*up));
337 pp->io.clock_recv = irig_receive;
338 pp->io.srcclock = peer;
341 if (!io_addclock(&pp->io)) {
350 * Initialize miscellaneous variables
352 peer->precision = PRECISION;
353 pp->clockdesc = DESCRIPTION;
354 memcpy((char *)&pp->refid, REFID, 4);
360 * The companded samples are encoded sign-magnitude. The table
361 * contains all the 256 values in the interest of speed.
363 up->comp[0] = up->comp[OFFSET] = 0.;
364 up->comp[1] = 1; up->comp[OFFSET + 1] = -1.;
365 up->comp[2] = 3; up->comp[OFFSET + 2] = -3.;
367 for (i = 3; i < OFFSET; i++) {
368 up->comp[i] = up->comp[i - 1] + step;
369 up->comp[OFFSET + i] = -up->comp[i];
373 DTOLFP(1. / SECOND, &up->tick);
379 * irig_shutdown - shut down the clock
383 int unit, /* instance number (not used) */
384 struct peer *peer /* peer structure pointer */
387 struct refclockproc *pp;
393 io_closeclock(&pp->io);
400 * irig_receive - receive data from the audio device
402 * This routine reads input samples and adjusts the logical clock to
403 * track the irig clock by dropping or duplicating codec samples.
407 struct recvbuf *rbufp /* receive buffer structure pointer */
411 struct refclockproc *pp;
417 double sample; /* codec sample */
418 u_char *dpt; /* buffer pointer */
419 int bufcnt; /* buffer counter */
420 l_fp ltemp; /* l_fp temp */
422 peer = rbufp->recv_peer;
427 * Main loop - read until there ain't no more. Note codec
428 * samples are bit-inverted.
430 DTOLFP((double)rbufp->recv_length / SECOND, <emp);
431 L_SUB(&rbufp->recv_time, <emp);
432 up->timestamp = rbufp->recv_time;
433 dpt = rbufp->recv_buffer;
434 for (bufcnt = 0; bufcnt < rbufp->recv_length; bufcnt++) {
435 sample = up->comp[~*dpt++ & 0xff];
438 * Variable frequency oscillator. The codec oscillator
439 * runs at the nominal rate of 8000 samples per second,
440 * or 125 us per sample. A frequency change of one unit
441 * results in either duplicating or deleting one sample
442 * per second, which results in a frequency change of
445 up->phase += (up->freq + clock_codec) / SECOND;
446 up->phase += pp->fudgetime2 / 1e6;
447 if (up->phase >= .5) {
449 } else if (up->phase < -.5) {
451 irig_rf(peer, sample);
452 irig_rf(peer, sample);
454 irig_rf(peer, sample);
456 L_ADD(&up->timestamp, &up->tick);
457 sample = fabs(sample);
458 if (sample > up->signal)
460 up->signal += (sample - up->signal) /
464 * Once each second, determine the IRIG format and gain.
466 up->seccnt = (up->seccnt + 1) % SECOND;
467 if (up->seccnt == 0) {
468 if (up->irig_b > up->irig_e) {
475 up->irig_b = up->irig_e = 0;
482 * Set the input port and monitor gain for the next buffer.
484 if (pp->sloppyclockflag & CLK_FLAG2)
488 if (pp->sloppyclockflag & CLK_FLAG3)
489 up->mongain = MONGAIN;
496 * irig_rf - RF processing
498 * This routine filters the RF signal using a bandass filter for IRIG-B
499 * and a lowpass filter for IRIG-E. In case of IRIG-E, the samples are
500 * decimated by a factor of ten. Note that the codec filters function as
501 * roofing filters to attenuate both the high and low ends of the
502 * passband. IIR filter coefficients were determined using Matlab Signal
503 * Processing Toolkit.
507 struct peer *peer, /* peer structure pointer */
508 double sample /* current signal sample */
511 struct refclockproc *pp;
517 double irig_b, irig_e; /* irig filter outputs */
523 * IRIG-B filter. Matlab 4th-order IIR elliptic, 800-1200 Hz
524 * bandpass, 0.3 dB passband ripple, -50 dB stopband ripple,
525 * phase delay 1.03 ms.
527 irig_b = (up->bpf[8] = up->bpf[7]) * 6.505491e-001;
528 irig_b += (up->bpf[7] = up->bpf[6]) * -3.875180e+000;
529 irig_b += (up->bpf[6] = up->bpf[5]) * 1.151180e+001;
530 irig_b += (up->bpf[5] = up->bpf[4]) * -2.141264e+001;
531 irig_b += (up->bpf[4] = up->bpf[3]) * 2.712837e+001;
532 irig_b += (up->bpf[3] = up->bpf[2]) * -2.384486e+001;
533 irig_b += (up->bpf[2] = up->bpf[1]) * 1.427663e+001;
534 irig_b += (up->bpf[1] = up->bpf[0]) * -5.352734e+000;
535 up->bpf[0] = sample - irig_b;
536 irig_b = up->bpf[0] * 4.952157e-003
537 + up->bpf[1] * -2.055878e-002
538 + up->bpf[2] * 4.401413e-002
539 + up->bpf[3] * -6.558851e-002
540 + up->bpf[4] * 7.462108e-002
541 + up->bpf[5] * -6.558851e-002
542 + up->bpf[6] * 4.401413e-002
543 + up->bpf[7] * -2.055878e-002
544 + up->bpf[8] * 4.952157e-003;
545 up->irig_b += irig_b * irig_b;
548 * IRIG-E filter. Matlab 4th-order IIR elliptic, 130-Hz lowpass,
549 * 0.3 dB passband ripple, -50 dB stopband ripple, phase delay
552 irig_e = (up->lpf[4] = up->lpf[3]) * 8.694604e-001;
553 irig_e += (up->lpf[3] = up->lpf[2]) * -3.589893e+000;
554 irig_e += (up->lpf[2] = up->lpf[1]) * 5.570154e+000;
555 irig_e += (up->lpf[1] = up->lpf[0]) * -3.849667e+000;
556 up->lpf[0] = sample - irig_e;
557 irig_e = up->lpf[0] * 3.215696e-003
558 + up->lpf[1] * -1.174951e-002
559 + up->lpf[2] * 1.712074e-002
560 + up->lpf[3] * -1.174951e-002
561 + up->lpf[4] * 3.215696e-003;
562 up->irig_e += irig_e * irig_e;
565 * Decimate by a factor of either 1 (IRIG-B) or 10 (IRIG-E).
567 up->badcnt = (up->badcnt + 1) % up->decim;
568 if (up->badcnt == 0) {
570 irig_base(peer, irig_b);
572 irig_base(peer, irig_e);
577 * irig_base - baseband processing
579 * This routine processes the baseband signal and demodulates the AM
580 * carrier using a synchronous detector. It then synchronizes to the
581 * data frame at the baud rate and decodes the width-modulated data
586 struct peer *peer, /* peer structure pointer */
587 double sample /* current signal sample */
590 struct refclockproc *pp;
596 double lope; /* integrator output */
597 double env; /* envelope detector output */
599 int carphase; /* carrier phase */
605 * Synchronous baud integrator. Corresponding samples of current
606 * and past baud intervals are integrated to refine the envelope
607 * amplitude and phase estimate. We keep one cycle (1 ms) of the
608 * raw data and one baud (10 ms) of the integrated data.
610 up->envphase = (up->envphase + 1) % BAUD;
611 up->integ[up->envphase] += (sample - up->integ[up->envphase]) /
613 lope = up->integ[up->envphase];
614 carphase = up->envphase % CYCLE;
615 up->lastenv[carphase] = sample;
616 up->lastint[carphase] = lope;
619 * Phase detector. Find the negative-going zero crossing
620 * relative to sample 4 in the 8-sample sycle. A phase change of
621 * 360 degrees produces an output change of one unit.
623 if (up->lastsig > 0 && lope <= 0)
624 up->zxing += (double)(carphase - 4) / CYCLE;
628 * End of the baud. Update signal/noise estimates and PLL
629 * phase, frequency and time constant.
631 if (up->envphase == 0) {
632 up->maxsignal = up->intmax; up->noise = up->intmin;
633 up->intmin = 1e6; up->intmax = -1e6;
634 if (up->maxsignal < DRPOUT)
635 up->errflg |= IRIG_ERR_AMP;
636 if (up->maxsignal > 0)
637 up->modndx = (up->maxsignal - up->noise) /
641 if (up->modndx < MODMIN)
642 up->errflg |= IRIG_ERR_MOD;
643 if (up->errflg & (IRIG_ERR_AMP | IRIG_ERR_FREQ |
644 IRIG_ERR_MOD | IRIG_ERR_SYNCH)) {
650 * Update PLL phase and frequency. The PLL time constant
651 * is set initially to stabilize the frequency within a
652 * minute or two, then increases to the maximum. The
653 * frequency is clamped so that the PLL capture range
654 * cannot be exceeded.
656 dtemp = up->zxing * up->decim / BAUD;
659 up->phase += dtemp / up->tc;
660 up->freq += dtemp / (4. * up->tc * up->tc);
661 if (up->freq > MAXFREQ) {
663 up->errflg |= IRIG_ERR_FREQ;
664 } else if (up->freq < -MAXFREQ) {
666 up->errflg |= IRIG_ERR_FREQ;
671 * Synchronous demodulator. There are eight samples in the cycle
672 * and ten cycles in the baud. Since the PLL has aligned the
673 * negative-going zero crossing at sample 4, the maximum
674 * amplitude is at sample 2 and minimum at sample 6. The
675 * beginning of the data pulse is determined from the integrated
676 * samples, while the end of the pulse is determined from the
677 * raw samples. The raw data bits are demodulated relative to
678 * the slice level and left-shifted in the decoding register.
683 lope = (up->lastint[2] - up->lastint[6]) / 2.;
684 if (lope > up->intmax)
686 if (lope < up->intmin)
690 * Pulse code demodulator and reference timestamp. The decoder
691 * looks for a sequence of ten bits; the first two bits must be
692 * one, the last two bits must be zero. Frame synch is asserted
693 * when three correct frames have been found.
695 up->pulse = (up->pulse + 1) % 10;
697 if (lope >= (up->maxsignal + up->noise) / 2.)
699 if ((up->cycles & 0x303c0f03) == 0x300c0300) {
701 up->errflg |= IRIG_ERR_SYNCH;
706 * Assemble the baud and max/min to get the slice level for the
707 * next baud. The slice level is based on the maximum over the
708 * first two bits and the minimum over the last two bits, with
709 * the slice level halfway between the maximum and minimum.
711 env = (up->lastenv[2] - up->lastenv[6]) / 2.;
713 if (env >= up->slice)
718 irig_baud(peer, up->dcycles);
719 if (env < up->envmin)
721 up->slice = (up->envmax + up->envmin) / 2;
722 up->envmin = 1e6; up->envmax = -1e6;
730 if (env > up->envmax)
741 * irig_baud - update the PLL and decode the pulse-width signal
745 struct peer *peer, /* peer structure pointer */
746 int bits /* decoded bits */
749 struct refclockproc *pp;
758 * The PLL time constant starts out small, in order to
759 * sustain a frequency tolerance of 250 PPM. It
760 * gradually increases as the loop settles down. Note
761 * that small wiggles are not believed, unless they
762 * persist for lots of samples.
764 up->exing = -up->yxing;
765 if (abs(up->envxing - up->envphase) <= 1) {
767 if (up->tcount > 20 * up->tc) {
772 up->envxing = up->envphase;
774 up->exing -= up->envxing - up->envphase;
778 up->envxing = up->envphase;
782 * Strike the baud timestamp as the positive zero crossing of
783 * the first bit, accounting for the codec delay and filter
786 up->prvstamp = up->chrstamp;
787 dtemp = up->decim * (up->exing / SECOND) + up->fdelay;
788 DTOLFP(dtemp, <emp);
789 up->chrstamp = up->timestamp;
790 L_SUB(&up->chrstamp, <emp);
793 * The data bits are collected in ten-bit bauds. The first two
794 * bits are not used. The resulting patterns represent runs of
795 * 0-1 bits (0), 2-4 bits (1) and 5-7 bits (PI). The remaining
796 * 8-bit run represents a soft error and is treated as 0.
798 switch (up->dcycles & 0xff) {
800 case 0x00: /* 0-1 bits (0) */
802 irig_decode(peer, BIT0);
805 case 0xc0: /* 2-4 bits (1) */
808 irig_decode(peer, BIT1);
811 case 0xf8: /* (5-7 bits (PI) */
814 irig_decode(peer, BITP);
817 default: /* 8 bits (error) */
818 irig_decode(peer, BIT0);
819 up->errflg |= IRIG_ERR_DECODE;
825 * irig_decode - decode the data
827 * This routine assembles bauds into digits, digits into frames and
828 * frames into the timecode fields. Bits can have values of zero, one
829 * or position identifier. There are four bits per digit, ten digits per
830 * frame and ten frames per second.
834 struct peer *peer, /* peer structure pointer */
835 int bit /* data bit (0, 1 or 2) */
838 struct refclockproc *pp;
844 int syncdig; /* sync digit (Spectracom) */
845 char sbs[6 + 1]; /* binary seconds since 0h */
846 char spare[2 + 1]; /* mulligan digits */
854 * Assemble frame bits.
859 } else if (bit == BITP && up->lastbit == BITP) {
862 * Frame sync - two adjacent position identifiers, which
863 * mark the beginning of the second. The reference time
864 * is the beginning of the second position identifier,
865 * so copy the character timestamp to the reference
869 up->errflg |= IRIG_ERR_SYNCH;
871 up->refstamp = up->prvstamp;
874 if (up->frmcnt % SUBFLD == 0) {
877 * End of frame. Encode two hexadecimal digits in
878 * little-endian timecode field. Note frame 1 is shifted
879 * right one bit to account for the marker PI.
882 if (up->frmcnt == 10)
885 up->timecode[--up->xptr] = hexchar[temp & 0xf];
886 up->timecode[--up->xptr] = hexchar[(temp >> 5) &
889 if (up->frmcnt == 0) {
892 * End of second. Decode the timecode and wind
893 * the clock. Not all IRIG generators have the
894 * year; if so, it is nonzero after year 2000.
895 * Not all have the hardware status bit; if so,
896 * it is lit when the source is okay and dim
897 * when bad. We watch this only if the year is
898 * nonzero. Not all are configured for signature
899 * control. If so, all BCD digits are set to
900 * zero if the source is bad. In this case the
901 * refclock_process() will reject the timecode
904 up->xptr = 2 * SUBFLD;
905 if (sscanf((char *)up->timecode,
906 "%6s%2d%1d%2s%3d%2d%2d%2d", sbs, &pp->year,
907 &syncdig, spare, &pp->day, &pp->hour,
908 &pp->minute, &pp->second) != 8)
909 pp->leap = LEAP_NOTINSYNC;
911 pp->leap = LEAP_NOWARNING;
912 up->second = (up->second + up->decim) % 60;
915 * Raise an alarm if the day field is zero,
916 * which happens when signature control is
917 * enabled and the device has lost
918 * synchronization. Raise an alarm if the year
919 * field is nonzero and the sync indicator is
920 * zero, which happens when a Spectracom radio
921 * has lost synchronization. Raise an alarm if
922 * the expected second does not agree with the
923 * decoded second, which happens with a garbled
924 * IRIG signal. We are very particular.
926 if (pp->day == 0 || (pp->year != 0 && syncdig ==
928 up->errflg |= IRIG_ERR_SIGERR;
929 if (pp->second != up->second)
930 up->errflg |= IRIG_ERR_CHECK;
931 up->second = pp->second;
934 * Wind the clock only if there are no errors
935 * and the time constant has reached the
938 if (up->errflg == 0 && up->tc == MAXTC) {
939 pp->lastref = pp->lastrec;
940 pp->lastrec = up->refstamp;
941 if (!refclock_process(pp))
942 refclock_report(peer,
945 snprintf(pp->a_lastcode, sizeof(pp->a_lastcode),
946 "%02x %02d %03d %02d:%02d:%02d %4.0f %3d %6.3f %2d %6.2f %6.1f %s",
947 up->errflg, pp->year, pp->day,
948 pp->hour, pp->minute, pp->second,
949 up->maxsignal, up->gain, up->modndx,
950 up->tc, up->exing * 1e6 / SECOND, up->freq *
951 1e6 / SECOND, ulfptoa(&pp->lastrec, 6));
952 pp->lencode = strlen(pp->a_lastcode);
954 if (pp->sloppyclockflag & CLK_FLAG4) {
955 record_clock_stats(&peer->srcadr,
965 up->frmcnt = (up->frmcnt + 1) % FIELD;
970 * irig_poll - called by the transmit procedure
972 * This routine sweeps up the timecode updates since the last poll. For
973 * IRIG-B there should be at least 60 updates; for IRIG-E there should
974 * be at least 6. If nothing is heard, a timeout event is declared.
978 int unit, /* instance number (not used) */
979 struct peer *peer /* peer structure pointer */
982 struct refclockproc *pp;
986 if (pp->coderecv == pp->codeproc) {
987 refclock_report(peer, CEVNT_TIMEOUT);
991 refclock_receive(peer);
992 if (!(pp->sloppyclockflag & CLK_FLAG4)) {
993 record_clock_stats(&peer->srcadr, pp->a_lastcode);
996 printf("irig %s\n", pp->a_lastcode);
1005 * irig_gain - adjust codec gain
1007 * This routine is called at the end of each second. It uses the AGC to
1008 * bradket the maximum signal level between MINAMP and MAXAMP to avoid
1009 * hunting. The routine also jiggles the input port and selectively
1010 * mutes the monitor.
1014 struct peer *peer /* peer structure pointer */
1017 struct refclockproc *pp;
1018 struct irigunit *up;
1024 * Apparently, the codec uses only the high order bits of the
1025 * gain control field. Thus, it may take awhile for changes to
1026 * wiggle the hardware bits.
1028 if (up->maxsignal < MINAMP) {
1030 if (up->gain > MAXGAIN)
1032 } else if (up->maxsignal > MAXAMP) {
1037 audio_gain(up->gain, up->mongain, up->port);
1042 int refclock_irig_bs;
1043 #endif /* REFCLOCK */