/*
* refclock_chu - clock driver for Canadian CHU time/frequency station
*/
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif
#if defined(REFCLOCK) && defined(CLOCK_CHU)
#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_AUDIO
#include "audio.h"
#endif /* HAVE_AUDIO */
#define ICOM 1 /* undefine to suppress ICOM code */
#ifdef ICOM
#include "icom.h"
#endif /* ICOM */
/*
* Audio CHU demodulator/decoder
*
* This driver synchronizes the computer time using data encoded in
* radio transmissions from Canadian time/frequency station CHU in
* Ottawa, Ontario. Transmissions are made continuously on 3330 kHz,
* 7850 kHz and 14670 kHz in upper sideband, compatible AM mode. An
* ordinary shortwave receiver can be tuned manually to one of these
* frequencies or, in the case of ICOM receivers, the receiver can be
* tuned automatically as propagation conditions change throughout the
* day and season.
*
* 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 driver can be compiled to use a Bell 103 compatible modem or
* modem chip to receive the radio signal and demodulate the data.
* Alternatively, the driver can be compiled to use the audio codec of
* the workstation or another with compatible audio drivers. In the
* latter case, the driver implements the modem using DSP routines, so
* the radio can be connected directly to either the microphone on line
* input port. In either case, the driver decodes the data using a
* maximum-likelihood technique which exploits the considerable degree
* of redundancy available to maximize accuracy and minimize errors.
*
* The CHU time broadcast includes an audio signal compatible with the
* Bell 103 modem standard (mark = 2225 Hz, space = 2025 Hz). The signal
* consists of nine, ten-character bursts transmitted at 300 bps between
* seconds 31 and 39 of each minute. Each character consists of eight
* data bits plus one start bit and two stop bits to encode two hex
* digits. The burst data consist of five characters (ten hex digits)
* followed by a repeat of these characters. In format A, the characters
* are repeated in the same polarity; in format B, the characters are
* repeated in the opposite polarity.
*
* Format A bursts are sent at seconds 32 through 39 of the minute in
* hex digits (nibble swapped)
*
* 6dddhhmmss6dddhhmmss
*
* The first ten digits encode a frame marker (6) followed by the day
* (ddd), hour (hh in UTC), minute (mm) and the second (ss). Since
* format A bursts are sent during the third decade of seconds the tens
* digit of ss is always 3. The driver uses this to determine correct
* burst synchronization. These digits are then repeated with the same
* polarity.
*
* Format B bursts are sent at second 31 of the minute in hex digits
*
* xdyyyyttaaxdyyyyttaa
*
* The first ten digits encode a code (x described below) followed by
* the DUT1 (d in deciseconds), Gregorian year (yyyy), difference TAI -
* UTC (tt) and daylight time indicator (aa) peculiar to Canada. These
* digits are then repeated with inverted polarity.
*
* The x is coded
*
* 1 Sign of DUT (0 = +)
* 2 Leap second warning. One second will be added.
* 4 Leap second warning. One second will be subtracted.
* 8 Even parity bit for this nibble.
*
* By design, the last stop bit of the last character in the burst
* coincides with 0.5 second. Since characters have 11 bits and are
* transmitted at 300 bps, the last stop bit of the first character
* coincides with 0.5 - 9 * 11/300 = 0.170 second. Depending on the
* UART, character interrupts can vary somewhere between the end of bit
* 9 and end of bit 11. These eccentricities can be corrected along with
* the radio propagation delay using fudge time 1.
*
* Debugging aids
*
* The timecode format used for debugging and data recording includes
* data helpful in diagnosing problems with the radio signal and serial
* connections. With debugging enabled (-d on the ntpd command line),
* the driver produces one line for each burst in two formats
* corresponding to format A and B.Each line begins with the format code
* chuA or chuB followed by the status code and signal level (0-9999).
* The remainder of the line is as follows.
*
* Following is format A:
*
* n b f s m code
*
* where n is the number of characters in the burst (0-10), b the burst
* distance (0-40), f the field alignment (-1, 0, 1), s the
* synchronization distance (0-16), m the burst number (2-9) and code
* the burst characters as received. Note that the hex digits in each
* character are reversed, so the burst
*
* 10 38 0 16 9 06851292930685129293
*
* is interpreted as containing 10 characters with burst distance 38,
* field alignment 0, synchronization distance 16 and burst number 9.
* The nibble-swapped timecode shows day 58, hour 21, minute 29 and
* second 39.
*
* Following is format B:
*
* n b s code
*
* where n is the number of characters in the burst (0-10), b the burst
* distance (0-40), s the synchronization distance (0-40) and code the
* burst characters as received. Note that the hex digits in each
* character are reversed and the last ten digits inverted, so the burst
*
* 10 40 1091891300ef6e76ec
*
* is interpreted as containing 10 characters with burst distance 40.
* The nibble-swapped timecode shows DUT1 +0.1 second, year 1998 and TAI
* - UTC 31 seconds.
*
* Each line is preceeded by the code chuA or chuB, as appropriate. If
* the audio driver is compiled, the current gain (0-255) and relative
* signal level (0-9999) follow the code. The receiver volume control
* should be set so that the gain is somewhere near the middle of the
* range 0-255, which results in a signal level near 1000.
*
* In addition to the above, the reference timecode is updated and
* written to the clockstats file and debug score after the last burst
* received in the minute. The format is
*
* sq yyyy ddd hh:mm:ss l s dd t agc ident m b
*
* s '?' before first synchronized and ' ' after that
* q status code (see below)
* yyyy year
* ddd day of year
* hh:mm:ss time of day
* l leap second indicator (space, L or D)
* dst Canadian daylight code (opaque)
* t number of minutes since last synchronized
* agc audio gain (0 - 255)
* ident identifier (CHU0 3330 kHz, CHU1 7850 kHz, CHU2 14670 kHz)
* m signal metric (0 - 100)
* b number of timecodes for the previous minute (0 - 59)
*
* Fudge factors
*
* For accuracies better than the low millisceconds, fudge time1 can be
* set to the radio propagation delay from CHU to the receiver. This can
* be done conviently using the minimuf program.
*
* Fudge flag4 causes the dubugging output described above to be
* recorded in the clockstats file. When the audio driver is compiled,
* 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 to a default value.
*
* The audio codec code is normally compiled in the driver if the
* architecture supports it (HAVE_AUDIO defined), but is used only if
* the link /dev/chu_audio is defined and valid. The serial port code is
* always compiled in the driver, but is used only if the autdio codec
* is not available and the link /dev/chu%d is defined and valid.
*
* The ICOM code is normally compiled in the driver if selected (ICOM
* defined), but is used only if the link /dev/icom%d is defined and
* valid and the mode keyword on the server configuration command
* specifies a nonzero mode (ICOM ID select code). The C-IV speed is
* 9600 bps if the high order 0x80 bit of the mode is zero and 1200 bps
* if one. The C-IV trace is turned on if the debug level is greater
* than one.
*
* Alarm codes
*
* CEVNT_BADTIME invalid date or time
* CEVNT_PROP propagation failure - no stations heard
*/
/*
* Interface definitions
*/
#define SPEED232 B300 /* uart speed (300 baud) */
#define PRECISION (-10) /* precision assumed (about 1 ms) */
#define REFID "CHU" /* reference ID */
#define DEVICE "/dev/chu%d" /* device name and unit */
#define SPEED232 B300 /* UART speed (300 baud) */
#ifdef ICOM
#define TUNE .001 /* offset for narrow filter (MHz) */
#define DWELL 5 /* minutes in a dwell */
#define NCHAN 3 /* number of channels */
#define ISTAGE 3 /* number of integrator stages */
#endif /* ICOM */
#ifdef HAVE_AUDIO
/*
* Audio demodulator definitions
*/
#define SECOND 8000 /* nominal sample rate (Hz) */
#define BAUD 300 /* modulation rate (bps) */
#define OFFSET 128 /* companded sample offset */
#define SIZE 256 /* decompanding table size */
#define MAXAMP 6000. /* maximum signal level */
#define MAXCLP 100 /* max clips above reference per s */
#define SPAN 800. /* min envelope span */
#define LIMIT 1000. /* soft limiter threshold */
#define AGAIN 6. /* baseband gain */
#define LAG 10 /* discriminator lag */
#define DEVICE_AUDIO "/dev/audio" /* device name */
#define DESCRIPTION "CHU Audio/Modem Receiver" /* WRU */
#define AUDIO_BUFSIZ 240 /* audio buffer size (30 ms) */
#else
#define DESCRIPTION "CHU Modem Receiver" /* WRU */
#endif /* HAVE_AUDIO */
/*
* Decoder definitions
*/
#define CHAR (11. / 300.) /* character time (s) */
#define BURST 11 /* max characters per burst */
#define MINCHAR 9 /* min characters per burst */
#define MINDIST 28 /* min burst distance (of 40) */
#define MINSYNC 8 /* min sync distance (of 16) */
#define MINSTAMP 20 /* min timestamps (of 60) */
#define MINMETRIC 50 /* min channel metric (of 160) */
/*
* The on-time synchronization point for the driver is the last stop bit
* of the first character 170 ms. The modem delay is 0.8 ms, while the
* receiver delay is approxmately 4.7 ms at 2125 Hz. The fudge value 1.3
* ms due to the codec and other causes was determined by calibrating to
* a PPS signal from a GPS receiver. The additional propagation delay
* specific to each receiver location can be programmed in the fudge
* time1.
*
* The resulting offsets with a 2.4-GHz P4 running FreeBSD 6.1 are
* generally within 0.5 ms short term with 0.3 ms jitter. The long-term
* offsets vary up to 0.3 ms due to ionospheric layer height variations.
* The processor load due to the driver is 0.4 percent.
*/
#define PDELAY ((170 + .8 + 4.7 + 1.3) / 1000) /* system delay (s) */
/*
* Status bits (status)
*/
#define RUNT 0x0001 /* runt burst */
#define NOISE 0x0002 /* noise burst */
#define BFRAME 0x0004 /* invalid format B frame sync */
#define BFORMAT 0x0008 /* invalid format B data */
#define AFRAME 0x0010 /* invalid format A frame sync */
#define AFORMAT 0x0020 /* invalid format A data */
#define DECODE 0x0040 /* invalid data decode */
#define STAMP 0x0080 /* too few timestamps */
#define AVALID 0x0100 /* valid A frame */
#define BVALID 0x0200 /* valid B frame */
#define INSYNC 0x0400 /* clock synchronized */
#define METRIC 0x0800 /* one or more stations heard */
/*
* Alarm status bits (alarm)
*
* These alarms are set at the end of a minute in which at least one
* burst was received. SYNERR is raised if the AFRAME or BFRAME status
* bits are set during the minute, FMTERR is raised if the AFORMAT or
* BFORMAT status bits are set, DECERR is raised if the DECODE status
* bit is set and TSPERR is raised if the STAMP status bit is set.
*/
#define SYNERR 0x01 /* frame sync error */
#define FMTERR 0x02 /* data format error */
#define DECERR 0x04 /* data decoding error */
#define TSPERR 0x08 /* insufficient data */
#ifdef HAVE_AUDIO
/*
* Maximum-likelihood UART structure. There are eight of these
* corresponding to the number of phases.
*/
struct surv {
l_fp cstamp; /* last bit timestamp */
double shift[12]; /* sample shift register */
double span; /* shift register envelope span */
double dist; /* sample distance */
int uart; /* decoded character */
};
#endif /* HAVE_AUDIO */
#ifdef ICOM
/*
* CHU station structure. There are three of these corresponding to the
* three frequencies.
*/
struct xmtr {
double integ[ISTAGE]; /* circular integrator */
double metric; /* integrator sum */
int iptr; /* integrator pointer */
int probe; /* dwells since last probe */
};
#endif /* ICOM */
/*
* CHU unit control structure
*/
struct chuunit {
u_char decode[20][16]; /* maximum-likelihood decoding matrix */
l_fp cstamp[BURST]; /* character timestamps */
l_fp tstamp[MAXSTAGE]; /* timestamp samples */
l_fp timestamp; /* current buffer timestamp */
l_fp laststamp; /* last buffer timestamp */
l_fp charstamp; /* character time as a l_fp */
int second; /* counts the seconds of the minute */
int errflg; /* error flags */
int status; /* status bits */
char ident[5]; /* station ID and channel */
#ifdef ICOM
int fd_icom; /* ICOM file descriptor */
int chan; /* radio channel */
int dwell; /* dwell cycle */
struct xmtr xmtr[NCHAN]; /* station metric */
#endif /* ICOM */
/*
* Character burst variables
*/
int cbuf[BURST]; /* character buffer */
int ntstamp; /* number of timestamp samples */
int ndx; /* buffer start index */
int prevsec; /* previous burst second */
int burdist; /* burst distance */
int syndist; /* sync distance */
int burstcnt; /* format A bursts this minute */
double maxsignal; /* signal level (modem only) */
int gain; /* codec gain (modem only) */
/*
* Format particulars
*/
int leap; /* leap/dut code */
int dut; /* UTC1 correction */
int tai; /* TAI - UTC correction */
int dst; /* Canadian DST code */
#ifdef HAVE_AUDIO
/*
* Audio codec variables
*/
int fd_audio; /* audio port file descriptor */
double comp[SIZE]; /* decompanding table */
int port; /* codec port */
int mongain; /* codec monitor gain */
int clipcnt; /* sample clip count */
int seccnt; /* second interval counter */
/*
* Modem variables
*/
l_fp tick; /* audio sample increment */
double bpf[9]; /* IIR bandpass filter */
double disc[LAG]; /* discriminator shift register */
double lpf[27]; /* FIR lowpass filter */
double monitor; /* audio monitor */
int discptr; /* discriminator pointer */
/*
* Maximum-likelihood UART variables
*/
double baud; /* baud interval */
struct surv surv[8]; /* UART survivor structures */
int decptr; /* decode pointer */
int decpha; /* decode phase */
int dbrk; /* holdoff counter */
#endif /* HAVE_AUDIO */
};
/*
* Function prototypes
*/
static int chu_start (int, struct peer *);
static void chu_shutdown (int, struct peer *);
static void chu_receive (struct recvbuf *);
static void chu_second (int, struct peer *);
static void chu_poll (int, struct peer *);
/*
* More function prototypes
*/
static void chu_decode (struct peer *, int, l_fp);
static void chu_burst (struct peer *);
static void chu_clear (struct peer *);
static void chu_a (struct peer *, int);
static void chu_b (struct peer *, int);
static int chu_dist (int, int);
static double chu_major (struct peer *);
#ifdef HAVE_AUDIO
static void chu_uart (struct surv *, double);
static void chu_rf (struct peer *, double);
static void chu_gain (struct peer *);
static void chu_audio_receive (struct recvbuf *rbufp);
#endif /* HAVE_AUDIO */
#ifdef ICOM
static int chu_newchan (struct peer *, double);
#endif /* ICOM */
static void chu_serial_receive (struct recvbuf *rbufp);
/*
* Global variables
*/
static char hexchar[] = "0123456789abcdef_*=";
#ifdef ICOM
/*
* Note the tuned frequencies are 1 kHz higher than the carrier. CHU
* transmits on USB with carrier so we can use AM and the narrow SSB
* filter.
*/
static double qsy[NCHAN] = {3.330, 7.850, 14.670}; /* freq (MHz) */
#endif /* ICOM */
/*
* Transfer vector
*/
struct refclock refclock_chu = {
chu_start, /* start up driver */
chu_shutdown, /* shut down driver */
chu_poll, /* transmit poll message */
noentry, /* not used (old chu_control) */
noentry, /* initialize driver (not used) */
noentry, /* not used (old chu_buginfo) */
chu_second /* housekeeping timer */
};
/*
* chu_start - open the devices and initialize data for processing
*/
static int
chu_start(
int unit, /* instance number (not used) */
struct peer *peer /* peer structure pointer */
)
{
struct chuunit *up;
struct refclockproc *pp;
char device[20]; /* device name */
int fd; /* file descriptor */
#ifdef ICOM
int temp;
#endif /* ICOM */
#ifdef HAVE_AUDIO
int fd_audio; /* audio port file descriptor */
int i; /* index */
double step; /* codec adjustment */
/*
* Open audio device. Don't complain if not there.
*/
fd_audio = audio_init(DEVICE_AUDIO, AUDIO_BUFSIZ, unit);
#ifdef DEBUG
if (fd_audio > 0 && debug)
audio_show();
#endif
/*
* If audio is unavailable, Open serial port in raw mode.
*/
if (fd_audio > 0) {
fd = fd_audio;
} else {
snprintf(device, sizeof(device), DEVICE, unit);
fd = refclock_open(device, SPEED232, LDISC_RAW);
}
#else /* HAVE_AUDIO */
/*
* Open serial port in raw mode.
*/
snprintf(device, sizeof(device), DEVICE, unit);
fd = refclock_open(device, SPEED232, LDISC_RAW);
#endif /* HAVE_AUDIO */
if (fd <= 0)
return (0);
/*
* Allocate and initialize unit structure
*/
up = emalloc(sizeof(*up));
memset(up, 0, sizeof(*up));
pp = peer->procptr;
pp->unitptr = (caddr_t)up;
pp->io.clock_recv = chu_receive;
pp->io.srcclock = (caddr_t)peer;
pp->io.datalen = 0;
pp->io.fd = fd;
if (!io_addclock(&pp->io)) {
close(fd);
pp->io.fd = -1;
free(up);
pp->unitptr = NULL;
return (0);
}
/*
* Initialize miscellaneous variables
*/
peer->precision = PRECISION;
pp->clockdesc = DESCRIPTION;
strcpy(up->ident, "CHU");
memcpy(&pp->refid, up->ident, 4);
DTOLFP(CHAR, &up->charstamp);
#ifdef HAVE_AUDIO
/*
* The companded samples are encoded sign-magnitude. The table
* contains all the 256 values in the interest of speed. We do
* this even if the audio codec is not available. C'est la lazy.
*/
up->fd_audio = fd_audio;
up->gain = 127;
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);
#endif /* HAVE_AUDIO */
#ifdef ICOM
temp = 0;
#ifdef DEBUG
if (debug > 1)
temp = P_TRACE;
#endif
if (peer->ttl > 0) {
if (peer->ttl & 0x80)
up->fd_icom = icom_init("/dev/icom", B1200,
temp);
else
up->fd_icom = icom_init("/dev/icom", B9600,
temp);
}
if (up->fd_icom > 0) {
if (chu_newchan(peer, 0) != 0) {
msyslog(LOG_NOTICE, "icom: radio not found");
close(up->fd_icom);
up->fd_icom = 0;
} else {
msyslog(LOG_NOTICE, "icom: autotune enabled");
}
}
#endif /* ICOM */
return (1);
}
/*
* chu_shutdown - shut down the clock
*/
static void
chu_shutdown(
int unit, /* instance number (not used) */
struct peer *peer /* peer structure pointer */
)
{
struct chuunit *up;
struct refclockproc *pp;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
if (up == NULL)
return;
io_closeclock(&pp->io);
#ifdef ICOM
if (up->fd_icom > 0)
close(up->fd_icom);
#endif /* ICOM */
free(up);
}
/*
* chu_receive - receive data from the audio or serial device
*/
static void
chu_receive(
struct recvbuf *rbufp /* receive buffer structure pointer */
)
{
#ifdef HAVE_AUDIO
struct chuunit *up;
struct refclockproc *pp;
struct peer *peer;
peer = (struct peer *)rbufp->recv_srcclock;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* If the audio codec is warmed up, the buffer contains codec
* samples which need to be demodulated and decoded into CHU
* characters using the software UART. Otherwise, the buffer
* contains CHU characters from the serial port, so the software
* UART is bypassed. In this case the CPU will probably run a
* few degrees cooler.
*/
if (up->fd_audio > 0)
chu_audio_receive(rbufp);
else
chu_serial_receive(rbufp);
#else
chu_serial_receive(rbufp);
#endif /* HAVE_AUDIO */
}
#ifdef HAVE_AUDIO
/*
* chu_audio_receive - receive data from the audio device
*/
static void
chu_audio_receive(
struct recvbuf *rbufp /* receive buffer structure pointer */
)
{
struct chuunit *up;
struct refclockproc *pp;
struct peer *peer;
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 chuunit *)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];
/*
* Clip noise spikes greater than MAXAMP. If no clips,
* increase the gain a tad; if the clips are too high,
* decrease a tad.
*/
if (sample > MAXAMP) {
sample = MAXAMP;
up->clipcnt++;
} else if (sample < -MAXAMP) {
sample = -MAXAMP;
up->clipcnt++;
}
chu_rf(peer, sample);
L_ADD(&up->timestamp, &up->tick);
/*
* Once each second ride gain.
*/
up->seccnt = (up->seccnt + 1) % SECOND;
if (up->seccnt == 0) {
chu_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;
}
/*
* chu_rf - filter and demodulate the FSK signal
*
* This routine implements a 300-baud Bell 103 modem with mark 2225 Hz
* and space 2025 Hz. It uses a bandpass filter followed by a soft
* limiter, FM discriminator and lowpass filter. A maximum-likelihood
* decoder samples the baseband signal at eight times the baud rate and
* detects the start bit of each character.
*
* The filters are built for speed, which explains the rather clumsy
* code. Hopefully, the compiler will efficiently implement the move-
* and-muiltiply-and-add operations.
*/
static void
chu_rf(
struct peer *peer, /* peer structure pointer */
double sample /* analog sample */
)
{
struct refclockproc *pp;
struct chuunit *up;
struct surv *sp;
/*
* Local variables
*/
double signal; /* bandpass signal */
double limit; /* limiter signal */
double disc; /* discriminator signal */
double lpf; /* lowpass signal */
double dist; /* UART signal distance */
int i, j;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* Bandpass filter. 4th-order elliptic, 500-Hz bandpass centered
* at 2125 Hz. Passband ripple 0.3 dB, stopband ripple 50 dB,
* phase delay 0.24 ms.
*/
signal = (up->bpf[8] = up->bpf[7]) * 5.844676e-01;
signal += (up->bpf[7] = up->bpf[6]) * 4.884860e-01;
signal += (up->bpf[6] = up->bpf[5]) * 2.704384e+00;
signal += (up->bpf[5] = up->bpf[4]) * 1.645032e+00;
signal += (up->bpf[4] = up->bpf[3]) * 4.644557e+00;
signal += (up->bpf[3] = up->bpf[2]) * 1.879165e+00;
signal += (up->bpf[2] = up->bpf[1]) * 3.522634e+00;
signal += (up->bpf[1] = up->bpf[0]) * 7.315738e-01;
up->bpf[0] = sample - signal;
signal = up->bpf[0] * 6.176213e-03
+ up->bpf[1] * 3.156599e-03
+ up->bpf[2] * 7.567487e-03
+ up->bpf[3] * 4.344580e-03
+ up->bpf[4] * 1.190128e-02
+ up->bpf[5] * 4.344580e-03
+ up->bpf[6] * 7.567487e-03
+ up->bpf[7] * 3.156599e-03
+ up->bpf[8] * 6.176213e-03;
up->monitor = signal / 4.; /* note monitor after filter */
/*
* Soft limiter/discriminator. The 11-sample discriminator lag
* interval corresponds to three cycles of 2125 Hz, which
* requires the sample frequency to be 2125 * 11 / 3 = 7791.7
* Hz. The discriminator output varies +-0.5 interval for input
* frequency 2025-2225 Hz. However, we don't get to sample at
* this frequency, so the discriminator output is biased. Life
* at 8000 Hz sucks.
*/
limit = signal;
if (limit > LIMIT)
limit = LIMIT;
else if (limit < -LIMIT)
limit = -LIMIT;
disc = up->disc[up->discptr] * -limit;
up->disc[up->discptr] = limit;
up->discptr = (up->discptr + 1 ) % LAG;
if (disc >= 0)
disc = SQRT(disc);
else
disc = -SQRT(-disc);
/*
* Lowpass filter. Raised cosine FIR, Ts = 1 / 300, beta = 0.1.
*/
lpf = (up->lpf[26] = up->lpf[25]) * 2.538771e-02;
lpf += (up->lpf[25] = up->lpf[24]) * 1.084671e-01;
lpf += (up->lpf[24] = up->lpf[23]) * 2.003159e-01;
lpf += (up->lpf[23] = up->lpf[22]) * 2.985303e-01;
lpf += (up->lpf[22] = up->lpf[21]) * 4.003697e-01;
lpf += (up->lpf[21] = up->lpf[20]) * 5.028552e-01;
lpf += (up->lpf[20] = up->lpf[19]) * 6.028795e-01;
lpf += (up->lpf[19] = up->lpf[18]) * 6.973249e-01;
lpf += (up->lpf[18] = up->lpf[17]) * 7.831828e-01;
lpf += (up->lpf[17] = up->lpf[16]) * 8.576717e-01;
lpf += (up->lpf[16] = up->lpf[15]) * 9.183463e-01;
lpf += (up->lpf[15] = up->lpf[14]) * 9.631951e-01;
lpf += (up->lpf[14] = up->lpf[13]) * 9.907208e-01;
lpf += (up->lpf[13] = up->lpf[12]) * 1.000000e+00;
lpf += (up->lpf[12] = up->lpf[11]) * 9.907208e-01;
lpf += (up->lpf[11] = up->lpf[10]) * 9.631951e-01;
lpf += (up->lpf[10] = up->lpf[9]) * 9.183463e-01;
lpf += (up->lpf[9] = up->lpf[8]) * 8.576717e-01;
lpf += (up->lpf[8] = up->lpf[7]) * 7.831828e-01;
lpf += (up->lpf[7] = up->lpf[6]) * 6.973249e-01;
lpf += (up->lpf[6] = up->lpf[5]) * 6.028795e-01;
lpf += (up->lpf[5] = up->lpf[4]) * 5.028552e-01;
lpf += (up->lpf[4] = up->lpf[3]) * 4.003697e-01;
lpf += (up->lpf[3] = up->lpf[2]) * 2.985303e-01;
lpf += (up->lpf[2] = up->lpf[1]) * 2.003159e-01;
lpf += (up->lpf[1] = up->lpf[0]) * 1.084671e-01;
lpf += up->lpf[0] = disc * 2.538771e-02;
/*
* Maximum-likelihood decoder. The UART updates each of the
* eight survivors and determines the span, slice level and
* tentative decoded character. Valid 11-bit characters are
* framed so that bit 10 and bit 11 (stop bits) are mark and bit
* 1 (start bit) is space. When a valid character is found, the
* survivor with maximum distance determines the final decoded
* character.
*/
up->baud += 1. / SECOND;
if (up->baud > 1. / (BAUD * 8.)) {
up->baud -= 1. / (BAUD * 8.);
up->decptr = (up->decptr + 1) % 8;
sp = &up->surv[up->decptr];
sp->cstamp = up->timestamp;
chu_uart(sp, -lpf * AGAIN);
if (up->dbrk > 0) {
up->dbrk--;
if (up->dbrk > 0)
return;
up->decpha = up->decptr;
}
if (up->decptr != up->decpha)
return;
dist = 0;
j = -1;
for (i = 0; i < 8; i++) {
/*
* The timestamp is taken at the last bit, so
* for correct decoding we reqire sufficient
* span and correct start bit and two stop bits.
*/
if ((up->surv[i].uart & 0x601) != 0x600 ||
up->surv[i].span < SPAN)
continue;
if (up->surv[i].dist > dist) {
dist = up->surv[i].dist;
j = i;
}
}
if (j < 0)
return;
/*
* Process the character, then blank the decoder until
* the end of the next character.This sets the decoding
* phase of the entire burst from the phase of the first
* character.
*/
up->maxsignal = up->surv[j].span;
chu_decode(peer, (up->surv[j].uart >> 1) & 0xff,
up->surv[j].cstamp);
up->dbrk = 88;
}
}
/*
* chu_uart - maximum-likelihood UART
*
* This routine updates a shift register holding the last 11 envelope
* samples. It then computes the slice level and span over these samples
* and determines the tentative data bits and distance. The calling
* program selects over the last eight survivors the one with maximum
* distance to determine the decoded character.
*/
static void
chu_uart(
struct surv *sp, /* survivor structure pointer */
double sample /* baseband signal */
)
{
double es_max, es_min; /* max/min envelope */
double slice; /* slice level */
double dist; /* distance */
double dtemp;
int i;
/*
* Save the sample and shift right. At the same time, measure
* the maximum and minimum over all eleven samples.
*/
es_max = -1e6;
es_min = 1e6;
sp->shift[0] = sample;
for (i = 11; i > 0; i--) {
sp->shift[i] = sp->shift[i - 1];
if (sp->shift[i] > es_max)
es_max = sp->shift[i];
if (sp->shift[i] < es_min)
es_min = sp->shift[i];
}
/*
* Determine the span as the maximum less the minimum and the
* slice level as the minimum plus a fraction of the span. Note
* the slight bias toward mark to correct for the modem tendency
* to make more mark than space errors. Compute the distance on
* the assumption the last two bits must be mark, the first
* space and the rest either mark or space.
*/
sp->span = es_max - es_min;
slice = es_min + .45 * sp->span;
dist = 0;
sp->uart = 0;
for (i = 1; i < 12; i++) {
sp->uart <<= 1;
dtemp = sp->shift[i];
if (dtemp > slice)
sp->uart |= 0x1;
if (i == 1 || i == 2) {
dist += dtemp - es_min;
} else if (i == 11) {
dist += es_max - dtemp;
} else {
if (dtemp > slice)
dist += dtemp - es_min;
else
dist += es_max - dtemp;
}
}
sp->dist = dist / (11 * sp->span);
}
#endif /* HAVE_AUDIO */
/*
* chu_serial_receive - receive data from the serial device
*/
static void
chu_serial_receive(
struct recvbuf *rbufp /* receive buffer structure pointer */
)
{
struct chuunit *up;
struct refclockproc *pp;
struct peer *peer;
u_char *dpt; /* receive buffer pointer */
peer = (struct peer *)rbufp->recv_srcclock;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
dpt = (u_char *)&rbufp->recv_space;
chu_decode(peer, *dpt, rbufp->recv_time);
}
/*
* chu_decode - decode the character data
*/
static void
chu_decode(
struct peer *peer, /* peer structure pointer */
int hexhex, /* data character */
l_fp cstamp /* data character timestamp */
)
{
struct refclockproc *pp;
struct chuunit *up;
l_fp tstmp; /* timestamp temp */
double dtemp;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* If the interval since the last character is greater than the
* longest burst, process the last burst and start a new one. If
* the interval is less than this but greater than two
* characters, consider this a noise burst and reject it.
*/
tstmp = up->timestamp;
if (L_ISZERO(&up->laststamp))
up->laststamp = up->timestamp;
L_SUB(&tstmp, &up->laststamp);
up->laststamp = up->timestamp;
LFPTOD(&tstmp, dtemp);
if (dtemp > BURST * CHAR) {
chu_burst(peer);
up->ndx = 0;
} else if (dtemp > 2.5 * CHAR) {
up->ndx = 0;
}
/*
* Append the character to the current burst and append the
* character timestamp to the timestamp list.
*/
if (up->ndx < BURST) {
up->cbuf[up->ndx] = hexhex & 0xff;
up->cstamp[up->ndx] = cstamp;
up->ndx++;
}
}
/*
* chu_burst - search for valid burst format
*/
static void
chu_burst(
struct peer *peer
)
{
struct chuunit *up;
struct refclockproc *pp;
int i;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* Correlate a block of five characters with the next block of
* five characters. The burst distance is defined as the number
* of bits that match in the two blocks for format A and that
* match the inverse for format B.
*/
if (up->ndx < MINCHAR) {
up->status |= RUNT;
return;
}
up->burdist = 0;
for (i = 0; i < 5 && i < up->ndx - 5; i++)
up->burdist += chu_dist(up->cbuf[i], up->cbuf[i + 5]);
/*
* If the burst distance is at least MINDIST, this must be a
* format A burst; if the value is not greater than -MINDIST, it
* must be a format B burst. If the B burst is perfect, we
* believe it; otherwise, it is a noise burst and of no use to
* anybody.
*/
if (up->burdist >= MINDIST) {
chu_a(peer, up->ndx);
} else if (up->burdist <= -MINDIST) {
chu_b(peer, up->ndx);
} else {
up->status |= NOISE;
return;
}
/*
* If this is a valid burst, wait a guard time of ten seconds to
* allow for more bursts, then arm the poll update routine to
* process the minute. Don't do this if this is called from the
* timer interrupt routine.
*/
if (peer->outdate != current_time)
peer->nextdate = current_time + 10;
}
/*
* chu_b - decode format B burst
*/
static void
chu_b(
struct peer *peer,
int nchar
)
{
struct refclockproc *pp;
struct chuunit *up;
u_char code[11]; /* decoded timecode */
char tbuf[80]; /* trace buffer */
char * p;
size_t chars;
size_t cb;
int i;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* In a format B burst, a character is considered valid only if
* the first occurence matches the last occurence. The burst is
* considered valid only if all characters are valid; that is,
* only if the distance is 40. Note that once a valid frame has
* been found errors are ignored.
*/
snprintf(tbuf, sizeof(tbuf), "chuB %04x %4.0f %2d %2d ",
up->status, up->maxsignal, nchar, -up->burdist);
cb = sizeof(tbuf);
p = tbuf;
for (i = 0; i < nchar; i++) {
chars = strlen(p);
if (cb < chars + 1) {
msyslog(LOG_ERR, "chu_b() fatal out buffer");
exit(1);
}
cb -= chars;
p += chars;
snprintf(p, cb, "%02x", up->cbuf[i]);
}
if (pp->sloppyclockflag & CLK_FLAG4)
record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
if (debug)
printf("%s\n", tbuf);
#endif
if (up->burdist > -40) {
up->status |= BFRAME;
return;
}
/*
* Convert the burst data to internal format. Don't bother with
* the timestamps.
*/
for (i = 0; i < 5; i++) {
code[2 * i] = hexchar[up->cbuf[i] & 0xf];
code[2 * i + 1] = hexchar[(up->cbuf[i] >>
4) & 0xf];
}
if (sscanf((char *)code, "%1x%1d%4d%2d%2x", &up->leap, &up->dut,
&pp->year, &up->tai, &up->dst) != 5) {
up->status |= BFORMAT;
return;
}
up->status |= BVALID;
if (up->leap & 0x8)
up->dut = -up->dut;
}
/*
* chu_a - decode format A burst
*/
static void
chu_a(
struct peer *peer,
int nchar
)
{
struct refclockproc *pp;
struct chuunit *up;
char tbuf[80]; /* trace buffer */
char * p;
size_t chars;
size_t cb;
l_fp offset; /* timestamp offset */
int val; /* distance */
int temp;
int i, j, k;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* Determine correct burst phase. There are three cases
* corresponding to in-phase, one character early or one
* character late. These cases are distinguished by the position
* of the framing digits 0x6 at positions 0 and 5 and 0x3 at
* positions 4 and 9. The correct phase is when the distance
* relative to the framing digits is maximum. The burst is valid
* only if the maximum distance is at least MINSYNC.
*/
up->syndist = k = 0;
val = -16;
for (i = -1; i < 2; i++) {
temp = up->cbuf[i + 4] & 0xf;
if (i >= 0)
temp |= (up->cbuf[i] & 0xf) << 4;
val = chu_dist(temp, 0x63);
temp = (up->cbuf[i + 5] & 0xf) << 4;
if (i + 9 < nchar)
temp |= up->cbuf[i + 9] & 0xf;
val += chu_dist(temp, 0x63);
if (val > up->syndist) {
up->syndist = val;
k = i;
}
}
/*
* Extract the second number; it must be in the range 2 through
* 9 and the two repititions must be the same.
*/
temp = (up->cbuf[k + 4] >> 4) & 0xf;
if (temp < 2 || temp > 9 || k + 9 >= nchar || temp !=
((up->cbuf[k + 9] >> 4) & 0xf))
temp = 0;
snprintf(tbuf, sizeof(tbuf),
"chuA %04x %4.0f %2d %2d %2d %2d %1d ", up->status,
up->maxsignal, nchar, up->burdist, k, up->syndist,
temp);
cb = sizeof(tbuf);
p = tbuf;
for (i = 0; i < nchar; i++) {
chars = strlen(p);
if (cb < chars + 1) {
msyslog(LOG_ERR, "chu_a() fatal out buffer");
exit(1);
}
cb -= chars;
p += chars;
snprintf(p, cb, "%02x", up->cbuf[i]);
}
if (pp->sloppyclockflag & CLK_FLAG4)
record_clock_stats(&peer->srcadr, tbuf);
#ifdef DEBUG
if (debug)
printf("%s\n", tbuf);
#endif
if (up->syndist < MINSYNC) {
up->status |= AFRAME;
return;
}
/*
* A valid burst requires the first seconds number to match the
* last seconds number. If so, the burst timestamps are
* corrected to the current minute and saved for later
* processing. In addition, the seconds decode is advanced from
* the previous burst to the current one.
*/
if (temp == 0) {
up->status |= AFORMAT;
} else {
up->status |= AVALID;
up->second = pp->second = 30 + temp;
offset.l_ui = 30 + temp;
offset.l_f = 0;
i = 0;
if (k < 0)
offset = up->charstamp;
else if (k > 0)
i = 1;
for (; i < nchar && i < k + 10; i++) {
up->tstamp[up->ntstamp] = up->cstamp[i];
L_SUB(&up->tstamp[up->ntstamp], &offset);
L_ADD(&offset, &up->charstamp);
if (up->ntstamp < MAXSTAGE - 1)
up->ntstamp++;
}
while (temp > up->prevsec) {
for (j = 15; j > 0; j--) {
up->decode[9][j] = up->decode[9][j - 1];
up->decode[19][j] =
up->decode[19][j - 1];
}
up->decode[9][j] = up->decode[19][j] = 0;
up->prevsec++;
}
}
/*
* Stash the data in the decoding matrix.
*/
i = -(2 * k);
for (j = 0; j < nchar; j++) {
if (i < 0 || i > 18) {
i += 2;
continue;
}
up->decode[i][up->cbuf[j] & 0xf]++;
i++;
up->decode[i][(up->cbuf[j] >> 4) & 0xf]++;
i++;
}
up->burstcnt++;
}
/*
* chu_poll - called by the transmit procedure
*/
static void
chu_poll(
int unit,
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
pp = peer->procptr;
pp->polls++;
}
/*
* chu_second - process minute data
*/
static void
chu_second(
int unit,
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
struct chuunit *up;
l_fp offset;
char synchar, qual, leapchar;
int minset, i;
double dtemp;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* This routine is called once per minute to process the
* accumulated burst data. We do a bit of fancy footwork so that
* this doesn't run while burst data are being accumulated.
*/
up->second = (up->second + 1) % 60;
if (up->second != 0)
return;
/*
* Process the last burst, if still in the burst buffer.
* If the minute contains a valid B frame with sufficient A
* frame metric, it is considered valid. However, the timecode
* is sent to clockstats even if invalid.
*/
chu_burst(peer);
minset = ((current_time - peer->update) + 30) / 60;
dtemp = chu_major(peer);
qual = 0;
if (up->status & (BFRAME | AFRAME))
qual |= SYNERR;
if (up->status & (BFORMAT | AFORMAT))
qual |= FMTERR;
if (up->status & DECODE)
qual |= DECERR;
if (up->status & STAMP)
qual |= TSPERR;
if (up->status & BVALID && dtemp >= MINMETRIC)
up->status |= INSYNC;
synchar = leapchar = ' ';
if (!(up->status & INSYNC)) {
pp->leap = LEAP_NOTINSYNC;
synchar = '?';
} else if (up->leap & 0x2) {
pp->leap = LEAP_ADDSECOND;
leapchar = 'L';
} else if (up->leap & 0x4) {
pp->leap = LEAP_DELSECOND;
leapchar = 'l';
} else {
pp->leap = LEAP_NOWARNING;
}
snprintf(pp->a_lastcode, sizeof(pp->a_lastcode),
"%c%1X %04d %03d %02d:%02d:%02d %c%x %+d %d %d %s %.0f %d",
synchar, qual, pp->year, pp->day, pp->hour, pp->minute,
pp->second, leapchar, up->dst, up->dut, minset, up->gain,
up->ident, dtemp, up->ntstamp);
pp->lencode = strlen(pp->a_lastcode);
/*
* If in sync and the signal metric is above threshold, the
* timecode is ipso fatso valid and can be selected to
* discipline the clock.
*/
if (up->status & INSYNC && !(up->status & (DECODE | STAMP)) &&
dtemp > MINMETRIC) {
if (!clocktime(pp->day, pp->hour, pp->minute, 0, GMT,
up->tstamp[0].l_ui, &pp->yearstart, &offset.l_ui)) {
up->errflg = CEVNT_BADTIME;
} else {
offset.l_uf = 0;
for (i = 0; i < up->ntstamp; i++)
refclock_process_offset(pp, offset,
up->tstamp[i], PDELAY +
pp->fudgetime1);
pp->lastref = up->timestamp;
refclock_receive(peer);
}
}
if (dtemp > 0)
record_clock_stats(&peer->srcadr, pp->a_lastcode);
#ifdef DEBUG
if (debug)
printf("chu: timecode %d %s\n", pp->lencode,
pp->a_lastcode);
#endif
#ifdef ICOM
chu_newchan(peer, dtemp);
#endif /* ICOM */
chu_clear(peer);
if (up->errflg)
refclock_report(peer, up->errflg);
up->errflg = 0;
}
/*
* chu_major - majority decoder
*/
static double
chu_major(
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
struct chuunit *up;
u_char code[11]; /* decoded timecode */
int metric; /* distance metric */
int val1; /* maximum distance */
int synchar; /* stray cat */
int temp;
int i, j, k;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* Majority decoder. Each burst encodes two replications at each
* digit position in the timecode. Each row of the decoding
* matrix encodes the number of occurences of each digit found
* at the corresponding position. The maximum over all
* occurrences at each position is the distance for this
* position and the corresponding digit is the maximum-
* likelihood candidate. If the distance is not more than half
* the total number of occurences, a majority has not been found
* and the data are discarded. The decoding distance is defined
* as the sum of the distances over the first nine digits. The
* tenth digit varies over the seconds, so we don't count it.
*/
metric = 0;
for (i = 0; i < 9; i++) {
val1 = 0;
k = 0;
for (j = 0; j < 16; j++) {
temp = up->decode[i][j] + up->decode[i + 10][j];
if (temp > val1) {
val1 = temp;
k = j;
}
}
if (val1 <= up->burstcnt)
up->status |= DECODE;
metric += val1;
code[i] = hexchar[k];
}
/*
* Compute the timecode timestamp from the days, hours and
* minutes of the timecode. Use clocktime() for the aggregate
* minutes and the minute offset computed from the burst
* seconds. Note that this code relies on the filesystem time
* for the years and does not use the years of the timecode.
*/
if (sscanf((char *)code, "%1x%3d%2d%2d", &synchar, &pp->day,
&pp->hour, &pp->minute) != 4)
up->status |= DECODE;
if (up->ntstamp < MINSTAMP)
up->status |= STAMP;
return (metric);
}
/*
* chu_clear - clear decoding matrix
*/
static void
chu_clear(
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
struct chuunit *up;
int i, j;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* Clear stuff for the minute.
*/
up->ndx = up->prevsec = 0;
up->burstcnt = up->ntstamp = 0;
up->status &= INSYNC | METRIC;
for (i = 0; i < 20; i++) {
for (j = 0; j < 16; j++)
up->decode[i][j] = 0;
}
}
#ifdef ICOM
/*
* chu_newchan - called once per minute to find the best channel;
* returns zero on success, nonzero if ICOM error.
*/
static int
chu_newchan(
struct peer *peer,
double met
)
{
struct chuunit *up;
struct refclockproc *pp;
struct xmtr *sp;
int rval;
double metric;
int i;
pp = peer->procptr;
up = (struct chuunit *)pp->unitptr;
/*
* The radio can be tuned to three channels: 0 (3330 kHz), 1
* (7850 kHz) and 2 (14670 kHz). There are five one-minute
* dwells in each cycle. During the first dwell the radio is
* tuned to one of the three channels to measure the channel
* metric. The channel is selected as the one least recently
* measured. During the remaining four dwells the radio is tuned
* to the channel with the highest channel metric.
*/
if (up->fd_icom <= 0)
return (0);
/*
* Update the current channel metric and age of all channels.
* Scan all channels for the highest metric.
*/
sp = &up->xmtr[up->chan];
sp->metric -= sp->integ[sp->iptr];
sp->integ[sp->iptr] = met;
sp->metric += sp->integ[sp->iptr];
sp->probe = 0;
sp->iptr = (sp->iptr + 1) % ISTAGE;
metric = 0;
for (i = 0; i < NCHAN; i++) {
up->xmtr[i].probe++;
if (up->xmtr[i].metric > metric) {
up->status |= METRIC;
metric = up->xmtr[i].metric;
up->chan = i;
}
}
/*
* Start the next dwell. If the first dwell or no stations have
* been heard, continue round-robin scan.
*/
up->dwell = (up->dwell + 1) % DWELL;
if (up->dwell == 0 || metric == 0) {
rval = 0;
for (i = 0; i < NCHAN; i++) {
if (up->xmtr[i].probe > rval) {
rval = up->xmtr[i].probe;
up->chan = i;
}
}
}
/* Retune the radio at each dwell in case somebody nudges the
* tuning knob.
*/
rval = icom_freq(up->fd_icom, peer->ttl & 0x7f, qsy[up->chan] +
TUNE);
snprintf(up->ident, sizeof(up->ident), "CHU%d", up->chan);
memcpy(&pp->refid, up->ident, 4);
memcpy(&peer->refid, up->ident, 4);
if (metric == 0 && up->status & METRIC) {
up->status &= ~METRIC;
refclock_report(peer, CEVNT_PROP);
}
return (rval);
}
#endif /* ICOM */
/*
* chu_dist - determine the distance of two octet arguments
*/
static int
chu_dist(
int x, /* an octet of bits */
int y /* another octet of bits */
)
{
int val; /* bit count */
int temp;
int i;
/*
* The distance is determined as the weight of the exclusive OR
* of the two arguments. The weight is determined by the number
* of one bits in the result. Each one bit increases the weight,
* while each zero bit decreases it.
*/
temp = x ^ y;
val = 0;
for (i = 0; i < 8; i++) {
if ((temp & 0x1) == 0)
val++;
else
val--;
temp >>= 1;
}
return (val);
}
#ifdef HAVE_AUDIO
/*
* chu_gain - adjust codec gain
*
* This routine is called at the end of each second. During the second
* the number of signal clips above the MAXAMP threshold (6000). If
* there are no clips, the gain is bumped up; if there are more than
* MAXCLP clips (100), it is bumped down. The decoder is relatively
* insensitive to amplitude, so this crudity works just peachy. The
* routine also jiggles the input port and selectively mutes the
*/
static void
chu_gain(
struct peer *peer /* peer structure pointer */
)
{
struct refclockproc *pp;
struct chuunit *up;
pp = peer->procptr;
up = (struct chuunit *)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->clipcnt == 0) {
up->gain += 4;
if (up->gain > MAXGAIN)
up->gain = MAXGAIN;
} else if (up->clipcnt > MAXCLP) {
up->gain -= 4;
if (up->gain < 0)
up->gain = 0;
}
audio_gain(up->gain, up->mongain, up->port);
up->clipcnt = 0;
}
#endif /* HAVE_AUDIO */
#else
int refclock_chu_bs;
#endif /* REFCLOCK */
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