/* * refclock_irig - audio IRIG-B/E demodulator/decoder */ #ifdef HAVE_CONFIG_H #include <config.h> #endif #if defined(REFCLOCK) && defined(CLOCK_IRIG) #include "ntpd.h" #include "ntp_io.h" #include "ntp_refclock.h" #include "ntp_calendar.h" #include "ntp_stdlib.h" #include <stdio.h> #include <ctype.h> #include <math.h> #ifdef HAVE_SYS_IOCTL_H #include <sys/ioctl.h> #endif /* HAVE_SYS_IOCTL_H */ #include "audio.h" /* * Audio IRIG-B/E demodulator/decoder * * This driver synchronizes the computer time using data encoded in * IRIG-B/E signals commonly produced by GPS receivers and other timing * devices. The IRIG signal is an amplitude-modulated carrier with * pulse-width modulated data bits. For IRIG-B, the carrier frequency is * 1000 Hz and bit rate 100 b/s; for IRIG-E, the carrier frequenchy is * 100 Hz and bit rate 10 b/s. The driver automatically recognizes which & format is in use. * * The driver requires an audio codec or sound card with sampling rate 8 * kHz and mu-law companding. This is the same standard as used by the * telephone industry and is supported by most hardware and operating * systems, including Solaris, SunOS, FreeBSD, NetBSD and Linux. In this * implementation, only one audio driver and codec can be supported on a * single machine. * * The program processes 8000-Hz mu-law companded samples using separate * signal filters for IRIG-B and IRIG-E, a comb filter, envelope * detector and automatic threshold corrector. Cycle crossings relative * to the corrected slice level determine the width of each pulse and * its value - zero, one or position identifier. * * The data encode 20 BCD digits which determine the second, minute, * hour and day of the year and sometimes the year and synchronization * condition. The comb filter exponentially averages the corresponding * samples of successive baud intervals in order to reliably identify * the reference carrier cycle. A type-II phase-lock loop (PLL) performs * additional integration and interpolation to accurately determine the * zero crossing of that cycle, which determines the reference * timestamp. A pulse-width discriminator demodulates the data pulses, * which are then encoded as the BCD digits of the timecode. * * The timecode and reference timestamp are updated once each second * with IRIG-B (ten seconds with IRIG-E) and local clock offset samples * saved for later processing. At poll intervals of 64 s, the saved * samples are processed by a trimmed-mean filter and used to update the * system clock. * * An automatic gain control feature provides protection against * overdriven or underdriven input signal amplitudes. It is designed to * maintain adequate demodulator signal amplitude while avoiding * occasional noise spikes. In order to assure reliable capture, the * decompanded input signal amplitude must be greater than 100 units and * the codec sample frequency error less than 250 PPM (.025 percent). * * Monitor Data * * The timecode format used for debugging and data recording includes * data helpful in diagnosing problems with the IRIG signal and codec * connections. The driver produces one line for each timecode in the * following format: * * 00 00 98 23 19:26:52 2782 143 0.694 10 0.3 66.5 3094572411.00027 * * If clockstats is enabled, the most recent line is written to the * clockstats file every 64 s. If verbose recording is enabled (fudge * flag 4) each line is written as generated. * * The first field containes the error flags in hex, where the hex bits * are interpreted as below. This is followed by the year of century, * day of year and time of day. Note that the time of day is for the * previous minute, not the current time. The status indicator and year * are not produced by some IRIG devices and appear as zeros. Following * these fields are the carrier amplitude (0-3000), codec gain (0-255), * modulation index (0-1), time constant (4-10), carrier phase error * +-.5) and carrier frequency error (PPM). The last field is the on- * time timestamp in NTP format. * * The error flags are defined as follows in hex: * * x01 Low signal. The carrier amplitude is less than 100 units. This * is usually the result of no signal or wrong input port. * x02 Frequency error. The codec frequency error is greater than 250 * PPM. This may be due to wrong signal format or (rarely) * defective codec. * x04 Modulation error. The IRIG modulation index is less than 0.5. * This is usually the result of an overdriven codec, wrong signal * format or wrong input port. * x08 Frame synch error. The decoder frame does not match the IRIG * frame. This is usually the result of an overdriven codec, wrong * signal format or noisy IRIG signal. It may also be the result of * an IRIG signature check which indicates a failure of the IRIG * signal synchronization source. * x10 Data bit error. The data bit length is out of tolerance. This is * usually the result of an overdriven codec, wrong signal format * or noisy IRIG signal. * x20 Seconds numbering discrepancy. The decoder second does not match * the IRIG second. This is usually the result of an overdriven * codec, wrong signal format or noisy IRIG signal. * x40 Codec error (overrun). The machine is not fast enough to keep up * with the codec. * x80 Device status error (Spectracom). * * * Once upon a time, an UltrSPARC 30 and Solaris 2.7 kept the clock * within a few tens of microseconds relative to the IRIG-B signal. * Accuracy with IRIG-E was about ten times worse. Unfortunately, Sun * broke the 2.7 audio driver in 2.8, which has a 10-ms sawtooth * modulation. * * Unlike other drivers, which can have multiple instantiations, this * one supports only one. It does not seem likely that more than one * audio codec would be useful in a single machine. More than one would * probably chew up too much CPU time anyway. * * Fudge factors * * Fudge flag4 causes the dubugging output described above to be * recorded in the clockstats file. Fudge flag2 selects the audio input * port, where 0 is the mike port (default) and 1 is the line-in port. * It does not seem useful to select the compact disc player port. Fudge * flag3 enables audio monitoring of the input signal. For this purpose, * the monitor gain is set t a default value. Fudgetime2 is used as a * frequency vernier for broken codec sample frequency. * * Alarm codes * * CEVNT_BADTIME invalid date or time * CEVNT_TIMEOUT no IRIG data since last poll */ /* * Interface definitions */ #define DEVICE_AUDIO "/dev/audio" /* audio device name */ #define PRECISION (-17) /* precision assumed (about 10 us) */ #define REFID "IRIG" /* reference ID */ #define DESCRIPTION "Generic IRIG Audio Driver" /* WRU */ #define AUDIO_BUFSIZ 320 /* audio buffer size (40 ms) */ #define SECOND 8000 /* nominal sample rate (Hz) */ #define BAUD 80 /* samples per baud interval */ #define OFFSET 128 /* companded sample offset */ #define SIZE 256 /* decompanding table size */ #define CYCLE 8 /* samples per bit */ #define SUBFLD 10 /* bits per frame */ #define FIELD 100 /* bits per second */ #define MINTC 2 /* min PLL time constant */ #define MAXTC 10 /* max PLL time constant max */ #define MAXAMP 3000. /* maximum signal amplitude */ #define MINAMP 2000. /* minimum signal amplitude */ #define DRPOUT 100. /* dropout signal amplitude */ #define MODMIN 0.5 /* minimum modulation index */ #define MAXFREQ (250e-6 * SECOND) /* freq tolerance (.025%) */ /* * The on-time synchronization point is the positive-going zero crossing * of the first cycle of the second. The IIR baseband filter phase delay * is 1.03 ms for IRIG-B and 3.47 ms for IRIG-E. The fudge value 2.68 ms * due to the codec and other causes was determined by calibrating to a * PPS signal from a GPS receiver. * * The results with a 2.4-GHz P4 running FreeBSD 6.1 are generally * within .02 ms short-term with .02 ms jitter. The processor load due * to the driver is 0.51 percent. */ #define IRIG_B ((1.03 + 2.68) / 1000) /* IRIG-B system delay (s) */ #define IRIG_E ((3.47 + 2.68) / 1000) /* IRIG-E system delay (s) */ /* * Data bit definitions */ #define BIT0 0 /* zero */ #define BIT1 1 /* one */ #define BITP 2 /* position identifier */ /* * Error flags */ #define IRIG_ERR_AMP 0x01 /* low carrier amplitude */ #define IRIG_ERR_FREQ 0x02 /* frequency tolerance exceeded */ #define IRIG_ERR_MOD 0x04 /* low modulation index */ #define IRIG_ERR_SYNCH 0x08 /* frame synch error */ #define IRIG_ERR_DECODE 0x10 /* frame decoding error */ #define IRIG_ERR_CHECK 0x20 /* second numbering discrepancy */ #define IRIG_ERR_ERROR 0x40 /* codec error (overrun) */ #define IRIG_ERR_SIGERR 0x80 /* IRIG status error (Spectracom) */ static char hexchar[] = "0123456789abcdef"; /* * IRIG unit control structure */ struct irigunit { u_char timecode[2 * SUBFLD + 1]; /* timecode string */ l_fp timestamp; /* audio sample timestamp */ l_fp tick; /* audio sample increment */ l_fp refstamp; /* reference timestamp */ l_fp chrstamp; /* baud timestamp */ l_fp prvstamp; /* previous baud timestamp */ double integ[BAUD]; /* baud integrator */ double phase, freq; /* logical clock phase and frequency */ double zxing; /* phase detector integrator */ double yxing; /* cycle phase */ double exing; /* envelope phase */ double modndx; /* modulation index */ double irig_b; /* IRIG-B signal amplitude */ double irig_e; /* IRIG-E signal amplitude */ int errflg; /* error flags */ /* * Audio codec variables */ double comp[SIZE]; /* decompanding table */ double signal; /* peak signal for AGC */ int port; /* codec port */ int gain; /* codec gain */ int mongain; /* codec monitor gain */ int seccnt; /* second interval counter */ /* * RF variables */ double bpf[9]; /* IRIG-B filter shift register */ double lpf[5]; /* IRIG-E filter shift register */ double envmin, envmax; /* envelope min and max */ double slice; /* envelope slice level */ double intmin, intmax; /* integrated envelope min and max */ double maxsignal; /* integrated peak amplitude */ double noise; /* integrated noise amplitude */ double lastenv[CYCLE]; /* last cycle amplitudes */ double lastint[CYCLE]; /* last integrated cycle amplitudes */ double lastsig; /* last carrier sample */ double fdelay; /* filter delay */ int decim; /* sample decimation factor */ int envphase; /* envelope phase */ int envptr; /* envelope phase pointer */ int envsw; /* envelope state */ int envxing; /* envelope slice crossing */ int tc; /* time constant */ int tcount; /* time constant counter */ int badcnt; /* decimation interval counter */ /* * Decoder variables */ int pulse; /* cycle counter */ int cycles; /* carrier cycles */ int dcycles; /* data cycles */ int lastbit; /* last code element */ int second; /* previous second */ int bitcnt; /* bit count in frame */ int frmcnt; /* bit count in second */ int xptr; /* timecode pointer */ int bits; /* demodulated bits */ }; /* * Function prototypes */ static int irig_start (int, struct peer *); static void irig_shutdown (int, struct peer *); static void irig_receive (struct recvbuf *); static void irig_poll (int, struct peer *); /* * More function prototypes */ static void irig_base (struct peer *, double); static void irig_rf (struct peer *, double); static void irig_baud (struct peer *, int); static void irig_decode (struct peer *, int); static void irig_gain (struct peer *); /* * Transfer vector */ struct refclock refclock_irig = { irig_start, /* start up driver */ irig_shutdown, /* shut down driver */ irig_poll, /* transmit poll message */ noentry, /* not used (old irig_control) */ noentry, /* initialize driver (not used) */ noentry, /* not used (old irig_buginfo) */ NOFLAGS /* not used */ }; /* * irig_start - open the devices and initialize data for processing */ static int irig_start( int unit, /* instance number (used for PCM) */ struct peer *peer /* peer structure pointer */ ) { struct refclockproc *pp; struct irigunit *up; /* * Local variables */ int fd; /* file descriptor */ int i; /* index */ double step; /* codec adjustment */ /* * Open audio device */ fd = audio_init(DEVICE_AUDIO, AUDIO_BUFSIZ, unit); if (fd < 0) return (0); #ifdef DEBUG if (debug) audio_show(); #endif /* * Allocate and initialize unit structure */ if (!(up = (struct irigunit *) emalloc(sizeof(struct irigunit)))) { (void) close(fd); return (0); } memset((char *)up, 0, sizeof(struct irigunit)); pp = peer->procptr; pp->unitptr = (caddr_t)up; pp->io.clock_recv = irig_receive; pp->io.srcclock = (caddr_t)peer; pp->io.datalen = 0; pp->io.fd = fd; if (!io_addclock(&pp->io)) { (void)close(fd); free(up); return (0); } /* * Initialize miscellaneous variables */ peer->precision = PRECISION; pp->clockdesc = DESCRIPTION; memcpy((char *)&pp->refid, REFID, 4); up->tc = MINTC; up->decim = 1; up->gain = 127; /* * The companded samples are encoded sign-magnitude. The table * contains all the 256 values in the interest of speed. */ up->comp[0] = up->comp[OFFSET] = 0.; up->comp[1] = 1; up->comp[OFFSET + 1] = -1.; up->comp[2] = 3; up->comp[OFFSET + 2] = -3.; step = 2.; for (i = 3; i < OFFSET; i++) { up->comp[i] = up->comp[i - 1] + step; up->comp[OFFSET + i] = -up->comp[i]; if (i % 16 == 0) step *= 2.; } DTOLFP(1. / SECOND, &up->tick); return (1); } /* * irig_shutdown - shut down the clock */ static void irig_shutdown( int unit, /* instance number (not used) */ struct peer *peer /* peer structure pointer */ ) { struct refclockproc *pp; struct irigunit *up; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; io_closeclock(&pp->io); free(up); } /* * irig_receive - receive data from the audio device * * This routine reads input samples and adjusts the logical clock to * track the irig clock by dropping or duplicating codec samples. */ static void irig_receive( struct recvbuf *rbufp /* receive buffer structure pointer */ ) { struct peer *peer; struct refclockproc *pp; struct irigunit *up; /* * Local variables */ double sample; /* codec sample */ u_char *dpt; /* buffer pointer */ int bufcnt; /* buffer counter */ l_fp ltemp; /* l_fp temp */ peer = (struct peer *)rbufp->recv_srcclock; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * Main loop - read until there ain't no more. Note codec * samples are bit-inverted. */ DTOLFP((double)rbufp->recv_length / SECOND, <emp); L_SUB(&rbufp->recv_time, <emp); up->timestamp = rbufp->recv_time; dpt = rbufp->recv_buffer; for (bufcnt = 0; bufcnt < rbufp->recv_length; bufcnt++) { sample = up->comp[~*dpt++ & 0xff]; /* * Variable frequency oscillator. The codec oscillator * runs at the nominal rate of 8000 samples per second, * or 125 us per sample. A frequency change of one unit * results in either duplicating or deleting one sample * per second, which results in a frequency change of * 125 PPM. */ up->phase += (up->freq + clock_codec) / SECOND; up->phase += pp->fudgetime2 / 1e6; if (up->phase >= .5) { up->phase -= 1.; } else if (up->phase < -.5) { up->phase += 1.; irig_rf(peer, sample); irig_rf(peer, sample); } else { irig_rf(peer, sample); } L_ADD(&up->timestamp, &up->tick); sample = fabs(sample); if (sample > up->signal) up->signal = sample; up->signal += (sample - up->signal) / 1000; /* * Once each second, determine the IRIG format and gain. */ up->seccnt = (up->seccnt + 1) % SECOND; if (up->seccnt == 0) { if (up->irig_b > up->irig_e) { up->decim = 1; up->fdelay = IRIG_B; } else { up->decim = 10; up->fdelay = IRIG_E; } up->irig_b = up->irig_e = 0; irig_gain(peer); } } /* * Set the input port and monitor gain for the next buffer. */ if (pp->sloppyclockflag & CLK_FLAG2) up->port = 2; else up->port = 1; if (pp->sloppyclockflag & CLK_FLAG3) up->mongain = MONGAIN; else up->mongain = 0; } /* * irig_rf - RF processing * * This routine filters the RF signal using a bandass filter for IRIG-B * and a lowpass filter for IRIG-E. In case of IRIG-E, the samples are * decimated by a factor of ten. Note that the codec filters function as * roofing filters to attenuate both the high and low ends of the * passband. IIR filter coefficients were determined using Matlab Signal * Processing Toolkit. */ static void irig_rf( struct peer *peer, /* peer structure pointer */ double sample /* current signal sample */ ) { struct refclockproc *pp; struct irigunit *up; /* * Local variables */ double irig_b, irig_e; /* irig filter outputs */ pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * IRIG-B filter. Matlab 4th-order IIR elliptic, 800-1200 Hz * bandpass, 0.3 dB passband ripple, -50 dB stopband ripple, * phase delay 1.03 ms. */ irig_b = (up->bpf[8] = up->bpf[7]) * 6.505491e-001; irig_b += (up->bpf[7] = up->bpf[6]) * -3.875180e+000; irig_b += (up->bpf[6] = up->bpf[5]) * 1.151180e+001; irig_b += (up->bpf[5] = up->bpf[4]) * -2.141264e+001; irig_b += (up->bpf[4] = up->bpf[3]) * 2.712837e+001; irig_b += (up->bpf[3] = up->bpf[2]) * -2.384486e+001; irig_b += (up->bpf[2] = up->bpf[1]) * 1.427663e+001; irig_b += (up->bpf[1] = up->bpf[0]) * -5.352734e+000; up->bpf[0] = sample - irig_b; irig_b = up->bpf[0] * 4.952157e-003 + up->bpf[1] * -2.055878e-002 + up->bpf[2] * 4.401413e-002 + up->bpf[3] * -6.558851e-002 + up->bpf[4] * 7.462108e-002 + up->bpf[5] * -6.558851e-002 + up->bpf[6] * 4.401413e-002 + up->bpf[7] * -2.055878e-002 + up->bpf[8] * 4.952157e-003; up->irig_b += irig_b * irig_b; /* * IRIG-E filter. Matlab 4th-order IIR elliptic, 130-Hz lowpass, * 0.3 dB passband ripple, -50 dB stopband ripple, phase delay * 3.47 ms. */ irig_e = (up->lpf[4] = up->lpf[3]) * 8.694604e-001; irig_e += (up->lpf[3] = up->lpf[2]) * -3.589893e+000; irig_e += (up->lpf[2] = up->lpf[1]) * 5.570154e+000; irig_e += (up->lpf[1] = up->lpf[0]) * -3.849667e+000; up->lpf[0] = sample - irig_e; irig_e = up->lpf[0] * 3.215696e-003 + up->lpf[1] * -1.174951e-002 + up->lpf[2] * 1.712074e-002 + up->lpf[3] * -1.174951e-002 + up->lpf[4] * 3.215696e-003; up->irig_e += irig_e * irig_e; /* * Decimate by a factor of either 1 (IRIG-B) or 10 (IRIG-E). */ up->badcnt = (up->badcnt + 1) % up->decim; if (up->badcnt == 0) { if (up->decim == 1) irig_base(peer, irig_b); else irig_base(peer, irig_e); } } /* * irig_base - baseband processing * * This routine processes the baseband signal and demodulates the AM * carrier using a synchronous detector. It then synchronizes to the * data frame at the baud rate and decodes the width-modulated data * pulses. */ static void irig_base( struct peer *peer, /* peer structure pointer */ double sample /* current signal sample */ ) { struct refclockproc *pp; struct irigunit *up; /* * Local variables */ double lope; /* integrator output */ double env; /* envelope detector output */ double dtemp; int carphase; /* carrier phase */ pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * Synchronous baud integrator. Corresponding samples of current * and past baud intervals are integrated to refine the envelope * amplitude and phase estimate. We keep one cycle (1 ms) of the * raw data and one baud (10 ms) of the integrated data. */ up->envphase = (up->envphase + 1) % BAUD; up->integ[up->envphase] += (sample - up->integ[up->envphase]) / (5 * up->tc); lope = up->integ[up->envphase]; carphase = up->envphase % CYCLE; up->lastenv[carphase] = sample; up->lastint[carphase] = lope; /* * Phase detector. Find the negative-going zero crossing * relative to sample 4 in the 8-sample sycle. A phase change of * 360 degrees produces an output change of one unit. */ if (up->lastsig > 0 && lope <= 0) up->zxing += (double)(carphase - 4) / CYCLE; up->lastsig = lope; /* * End of the baud. Update signal/noise estimates and PLL * phase, frequency and time constant. */ if (up->envphase == 0) { up->maxsignal = up->intmax; up->noise = up->intmin; up->intmin = 1e6; up->intmax = -1e6; if (up->maxsignal < DRPOUT) up->errflg |= IRIG_ERR_AMP; if (up->maxsignal > 0) up->modndx = (up->maxsignal - up->noise) / up->maxsignal; else up->modndx = 0; if (up->modndx < MODMIN) up->errflg |= IRIG_ERR_MOD; if (up->errflg & (IRIG_ERR_AMP | IRIG_ERR_FREQ | IRIG_ERR_MOD | IRIG_ERR_SYNCH)) { up->tc = MINTC; up->tcount = 0; } /* * Update PLL phase and frequency. The PLL time constant * is set initially to stabilize the frequency within a * minute or two, then increases to the maximum. The * frequency is clamped so that the PLL capture range * cannot be exceeded. */ dtemp = up->zxing * up->decim / BAUD; up->yxing = dtemp; up->zxing = 0.; up->phase += dtemp / up->tc; up->freq += dtemp / (4. * up->tc * up->tc); if (up->freq > MAXFREQ) { up->freq = MAXFREQ; up->errflg |= IRIG_ERR_FREQ; } else if (up->freq < -MAXFREQ) { up->freq = -MAXFREQ; up->errflg |= IRIG_ERR_FREQ; } } /* * Synchronous demodulator. There are eight samples in the cycle * and ten cycles in the baud. Since the PLL has aligned the * negative-going zero crossing at sample 4, the maximum * amplitude is at sample 2 and minimum at sample 6. The * beginning of the data pulse is determined from the integrated * samples, while the end of the pulse is determined from the * raw samples. The raw data bits are demodulated relative to * the slice level and left-shifted in the decoding register. */ if (carphase != 7) return; lope = (up->lastint[2] - up->lastint[6]) / 2.; if (lope > up->intmax) up->intmax = lope; if (lope < up->intmin) up->intmin = lope; /* * Pulse code demodulator and reference timestamp. The decoder * looks for a sequence of ten bits; the first two bits must be * one, the last two bits must be zero. Frame synch is asserted * when three correct frames have been found. */ up->pulse = (up->pulse + 1) % 10; up->cycles <<= 1; if (lope >= (up->maxsignal + up->noise) / 2.) up->cycles |= 1; if ((up->cycles & 0x303c0f03) == 0x300c0300) { if (up->pulse != 0) up->errflg |= IRIG_ERR_SYNCH; up->pulse = 0; } /* * Assemble the baud and max/min to get the slice level for the * next baud. The slice level is based on the maximum over the * first two bits and the minimum over the last two bits, with * the slice level halfway between the maximum and minimum. */ env = (up->lastenv[2] - up->lastenv[6]) / 2.; up->dcycles <<= 1; if (env >= up->slice) up->dcycles |= 1; switch(up->pulse) { case 0: irig_baud(peer, up->dcycles); if (env < up->envmin) up->envmin = env; up->slice = (up->envmax + up->envmin) / 2; up->envmin = 1e6; up->envmax = -1e6; break; case 1: up->envmax = env; break; case 2: if (env > up->envmax) up->envmax = env; break; case 9: up->envmin = env; break; } } /* * irig_baud - update the PLL and decode the pulse-width signal */ static void irig_baud( struct peer *peer, /* peer structure pointer */ int bits /* decoded bits */ ) { struct refclockproc *pp; struct irigunit *up; double dtemp; l_fp ltemp; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * The PLL time constant starts out small, in order to * sustain a frequency tolerance of 250 PPM. It * gradually increases as the loop settles down. Note * that small wiggles are not believed, unless they * persist for lots of samples. */ up->exing = -up->yxing; if (fabs(up->envxing - up->envphase) <= 1) { up->tcount++; if (up->tcount > 20 * up->tc) { up->tc++; if (up->tc > MAXTC) up->tc = MAXTC; up->tcount = 0; up->envxing = up->envphase; } else { up->exing -= up->envxing - up->envphase; } } else { up->tcount = 0; up->envxing = up->envphase; } /* * Strike the baud timestamp as the positive zero crossing of * the first bit, accounting for the codec delay and filter * delay. */ up->prvstamp = up->chrstamp; dtemp = up->decim * (up->exing / SECOND) + up->fdelay; DTOLFP(dtemp, <emp); up->chrstamp = up->timestamp; L_SUB(&up->chrstamp, <emp); /* * The data bits are collected in ten-bit bauds. The first two * bits are not used. The resulting patterns represent runs of * 0-1 bits (0), 2-4 bits (1) and 5-7 bits (PI). The remaining * 8-bit run represents a soft error and is treated as 0. */ switch (up->dcycles & 0xff) { case 0x00: /* 0-1 bits (0) */ case 0x80: irig_decode(peer, BIT0); break; case 0xc0: /* 2-4 bits (1) */ case 0xe0: case 0xf0: irig_decode(peer, BIT1); break; case 0xf8: /* (5-7 bits (PI) */ case 0xfc: case 0xfe: irig_decode(peer, BITP); break; default: /* 8 bits (error) */ irig_decode(peer, BIT0); up->errflg |= IRIG_ERR_DECODE; } } /* * irig_decode - decode the data * * This routine assembles bauds into digits, digits into frames and * frames into the timecode fields. Bits can have values of zero, one * or position identifier. There are four bits per digit, ten digits per * frame and ten frames per second. */ static void irig_decode( struct peer *peer, /* peer structure pointer */ int bit /* data bit (0, 1 or 2) */ ) { struct refclockproc *pp; struct irigunit *up; /* * Local variables */ int syncdig; /* sync digit (Spectracom) */ char sbs[6]; /* binary seconds since 0h */ char spare[2]; /* mulligan digits */ int temp; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * Assemble frame bits. */ up->bits >>= 1; if (bit == BIT1) { up->bits |= 0x200; } else if (bit == BITP && up->lastbit == BITP) { /* * Frame sync - two adjacent position identifiers, which * mark the beginning of the second. The reference time * is the beginning of the second position identifier, * so copy the character timestamp to the reference * timestamp. */ if (up->frmcnt != 1) up->errflg |= IRIG_ERR_SYNCH; up->frmcnt = 1; up->refstamp = up->prvstamp; } up->lastbit = bit; if (up->frmcnt % SUBFLD == 0) { /* * End of frame. Encode two hexadecimal digits in * little-endian timecode field. Note frame 1 is shifted * right one bit to account for the marker PI. */ temp = up->bits; if (up->frmcnt == 10) temp >>= 1; if (up->xptr >= 2) { up->timecode[--up->xptr] = hexchar[temp & 0xf]; up->timecode[--up->xptr] = hexchar[(temp >> 5) & 0xf]; } if (up->frmcnt == 0) { /* * End of second. Decode the timecode and wind * the clock. Not all IRIG generators have the * year; if so, it is nonzero after year 2000. * Not all have the hardware status bit; if so, * it is lit when the source is okay and dim * when bad. We watch this only if the year is * nonzero. Not all are configured for signature * control. If so, all BCD digits are set to * zero if the source is bad. In this case the * refclock_process() will reject the timecode * as invalid. */ up->xptr = 2 * SUBFLD; if (sscanf((char *)up->timecode, "%6s%2d%1d%2s%3d%2d%2d%2d", sbs, &pp->year, &syncdig, spare, &pp->day, &pp->hour, &pp->minute, &pp->second) != 8) pp->leap = LEAP_NOTINSYNC; else pp->leap = LEAP_NOWARNING; up->second = (up->second + up->decim) % 60; /* * Raise an alarm if the day field is zero, * which happens when signature control is * enabled and the device has lost * synchronization. Raise an alarm if the year * field is nonzero and the sync indicator is * zero, which happens when a Spectracom radio * has lost synchronization. Raise an alarm if * the expected second does not agree with the * decoded second, which happens with a garbled * IRIG signal. We are very particular. */ if (pp->day == 0 || (pp->year != 0 && syncdig == 0)) up->errflg |= IRIG_ERR_SIGERR; if (pp->second != up->second) up->errflg |= IRIG_ERR_CHECK; up->second = pp->second; /* * Wind the clock only if there are no errors * and the time constant has reached the * maximum. */ if (up->errflg == 0 && up->tc == MAXTC) { pp->lastref = pp->lastrec; pp->lastrec = up->refstamp; if (!refclock_process(pp)) refclock_report(peer, CEVNT_BADTIME); } sprintf(pp->a_lastcode, "%02x %02d %03d %02d:%02d:%02d %4.0f %3d %6.3f %2d %6.2f %6.1f %s", up->errflg, pp->year, pp->day, pp->hour, pp->minute, pp->second, up->maxsignal, up->gain, up->modndx, up->tc, up->exing * 1e6 / SECOND, up->freq * 1e6 / SECOND, ulfptoa(&pp->lastrec, 6)); pp->lencode = strlen(pp->a_lastcode); up->errflg = 0; if (pp->sloppyclockflag & CLK_FLAG4) { record_clock_stats(&peer->srcadr, pp->a_lastcode); #ifdef DEBUG if (debug) printf("irig %s\n", pp->a_lastcode); #endif /* DEBUG */ } } } up->frmcnt = (up->frmcnt + 1) % FIELD; } /* * irig_poll - called by the transmit procedure * * This routine sweeps up the timecode updates since the last poll. For * IRIG-B there should be at least 60 updates; for IRIG-E there should * be at least 6. If nothing is heard, a timeout event is declared. */ static void irig_poll( int unit, /* instance number (not used) */ struct peer *peer /* peer structure pointer */ ) { struct refclockproc *pp; struct irigunit *up; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; if (pp->coderecv == pp->codeproc) { refclock_report(peer, CEVNT_TIMEOUT); return; } refclock_receive(peer); if (!(pp->sloppyclockflag & CLK_FLAG4)) { record_clock_stats(&peer->srcadr, pp->a_lastcode); #ifdef DEBUG if (debug) printf("irig %s\n", pp->a_lastcode); #endif /* DEBUG */ } pp->polls++; } /* * irig_gain - adjust codec gain * * This routine is called at the end of each second. It uses the AGC to * bradket the maximum signal level between MINAMP and MAXAMP to avoid * hunting. The routine also jiggles the input port and selectively * mutes the monitor. */ static void irig_gain( struct peer *peer /* peer structure pointer */ ) { struct refclockproc *pp; struct irigunit *up; pp = peer->procptr; up = (struct irigunit *)pp->unitptr; /* * Apparently, the codec uses only the high order bits of the * gain control field. Thus, it may take awhile for changes to * wiggle the hardware bits. */ if (up->maxsignal < MINAMP) { up->gain += 4; if (up->gain > MAXGAIN) up->gain = MAXGAIN; } else if (up->maxsignal > MAXAMP) { up->gain -= 4; if (up->gain < 0) up->gain = 0; } audio_gain(up->gain, up->mongain, up->port); } #else int refclock_irig_bs; #endif /* REFCLOCK */