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minimodem-mirror/src/minimodem.c

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/*
* minimodem.c
*
* minimodem - software audio Bell-type or RTTY FSK modem
*
* Copyright (C) 2011 Kamal Mostafa <kamal@whence.com>
*
* This program is free software: you can redistribute it and/or modify
* it under the terms of the GNU General Public License as published by
* the Free Software Foundation, either version 3 of the License, or
* (at your option) any later version.
*
* This program is distributed in the hope that it will be useful,
* but WITHOUT ANY WARRANTY; without even the implied warranty of
* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
* GNU General Public License for more details.
*
* You should have received a copy of the GNU General Public License
* along with this program. If not, see <http://www.gnu.org/licenses/>.
*/
#include <getopt.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <ctype.h>
#include <math.h>
#include <assert.h>
#include <signal.h>
#include <sys/time.h>
#ifdef HAVE_CONFIG_H
#include "config.h"
#else
#define VERSION "unknown"
#endif
#include "simpleaudio.h"
#include "fsk.h"
#include "baudot.h"
char *program_name = "";
/*
* ASCII 8-bit data framebits decoder/encoder (passthrough)
*/
/* returns the number of datawords stuffed into *databits_outp */
int
framebits_encode_ascii8( unsigned int *databits_outp, char char_out )
{
*databits_outp = char_out;
return 1;
}
/* returns nbytes decoded */
static unsigned int
framebits_decode_ascii8( char *dataout_p, unsigned int dataout_size,
unsigned int bits )
{
if ( dataout_p == NULL ) // frame processor reset: noop
return 0;
assert( (bits & ~0xFF) == 0 );
assert( dataout_size >= 1);
*dataout_p = bits;
return 1;
}
/*
* Baudot 5-bit data framebits decoder/encoder
*/
#define framebits_encode_baudot baudot_encode
/* returns nbytes decoded */
static unsigned int
framebits_decode_baudot( char *dataout_p, unsigned int dataout_size,
unsigned int bits )
{
if ( dataout_p == NULL ) { // frame processor reset: reset Baudot state
baudot_reset();
return 0;
}
assert( (bits & ~0x1F) == 0 );
assert( dataout_size >= 1);
return baudot_decode(dataout_p, bits);
}
int tx_transmitting = 0;
int tx_leader_bits_len = 2;
int tx_trailer_bits_len = 2;
simpleaudio *tx_sa_out;
float tx_bfsk_mark_f;
unsigned int tx_bit_nsamples;
void
tx_stop_transmit_sighandler( int sig )
{
// fprintf(stderr, "alarm\n");
int j;
for ( j=0; j<tx_trailer_bits_len; j++ )
simpleaudio_tone(tx_sa_out, tx_bfsk_mark_f, tx_bit_nsamples);
// 0.5 sec of zero samples to flush - FIXME lame
size_t sample_rate = simpleaudio_get_rate(tx_sa_out);
simpleaudio_tone(tx_sa_out, 0, sample_rate/2);
tx_transmitting = 0;
}
/*
* rudimentary BFSK transmitter
*/
static void fsk_transmit_stdin(
simpleaudio *sa_out,
int tx_interactive,
float data_rate,
float bfsk_mark_f,
float bfsk_space_f,
int n_data_bits,
float bfsk_txstopbits,
int (*framebits_encoder)( unsigned int *databits_outp, char char_out )
)
{
size_t sample_rate = simpleaudio_get_rate(sa_out);
size_t bit_nsamples = sample_rate / data_rate + 0.5;
int c;
tx_sa_out = sa_out;
tx_bfsk_mark_f = bfsk_mark_f;
tx_bit_nsamples = bit_nsamples;
// one-shot
struct itimerval itv = {
{0, 0}, // it_interval
{0, 1000000/(float)(data_rate+data_rate*0.03) } // it_value
};
if ( tx_interactive )
signal(SIGALRM, tx_stop_transmit_sighandler);
tx_transmitting = 0;
while ( (c = getchar()) != EOF )
{
if ( tx_interactive )
setitimer(ITIMER_REAL, NULL, NULL);
// fprintf(stderr, "<c=%d>", c);
unsigned int nwords;
unsigned int bits[2];
nwords = framebits_encoder(bits, c);
if ( !tx_transmitting )
{
tx_transmitting = 1;
int j;
for ( j=0; j<tx_leader_bits_len; j++ )
simpleaudio_tone(sa_out, bfsk_mark_f, bit_nsamples);
}
unsigned int j;
for ( j=0; j<nwords; j++ ) {
simpleaudio_tone(sa_out, bfsk_space_f, bit_nsamples); // start
int i;
for ( i=0; i<n_data_bits; i++ ) { // data
unsigned int bit = ( bits[j] >> i ) & 1;
float tone_freq = bit == 1 ? bfsk_mark_f : bfsk_space_f;
simpleaudio_tone(sa_out, tone_freq, bit_nsamples);
}
simpleaudio_tone(sa_out, bfsk_mark_f,
bit_nsamples * bfsk_txstopbits); // stop
}
if ( tx_interactive )
setitimer(ITIMER_REAL, &itv, NULL);
}
if ( tx_interactive ) {
setitimer(ITIMER_REAL, NULL, NULL);
signal(SIGALRM, SIG_DFL);
}
if ( !tx_transmitting )
return;
tx_stop_transmit_sighandler(0);
}
static void
report_no_carrier( fsk_plan *fskp,
unsigned int sample_rate,
float bfsk_data_rate,
float nsamples_per_bit,
unsigned int nframes_decoded,
size_t carrier_nsamples,
float confidence_total )
{
unsigned long long nbits_total = nframes_decoded * (fskp->n_data_bits+2);
#if 0
fprintf(stderr, "nframes_decoded=%u\n", nframes_decoded);
fprintf(stderr, "nbits_total=%llu\n", nbits_total);
fprintf(stderr, "carrier_nsamples=%lu\n", carrier_nsamples);
fprintf(stderr, "nsamples_per_bit=%f\n", nsamples_per_bit);
#endif
float throughput_rate = nbits_total * sample_rate / (float)carrier_nsamples;
fprintf(stderr, "### NOCARRIER ndata=%u confidence=%.2f throughput=%.2f",
nframes_decoded,
confidence_total / nframes_decoded,
throughput_rate);
if ( (size_t)(nbits_total * nsamples_per_bit + 0.5) == carrier_nsamples ) {
fprintf(stderr, " (rate perfect) ###\n");
} else {
float throughput_skew = (throughput_rate - bfsk_data_rate)
/ bfsk_data_rate;
fprintf(stderr, " (%.1f%% %s) ###\n",
fabs(throughput_skew) * 100.0,
signbit(throughput_skew) ? "slow" : "fast"
);
}
}
void
generate_test_tones( simpleaudio *sa_out, unsigned int duration_sec )
{
unsigned int sample_rate = simpleaudio_get_rate(sa_out);
unsigned int nframes = sample_rate / 10;
int i;
for ( i=0; i<(sample_rate/nframes*duration_sec); i++ ) {
simpleaudio_tone(sa_out, 1000, nframes/2);
simpleaudio_tone(sa_out, 1777, nframes/2);
}
}
static int
benchmarks()
{
fprintf(stdout, "minimodem %s benchmarks\n", VERSION);
int ret;
ret = system("sed -n '/^model name/{p;q}' /proc/cpuinfo");
ret = ret; // don't care, hush compiler.
fflush(stdout);
unsigned int sample_rate = 48000;
sa_backend_t backend = SA_BACKEND_BENCHMARK;
// backend = SA_BACKEND_SYSDEFAULT; // for test
simpleaudio *sa_out;
// enable the sine wave LUT
simpleaudio_tone_init(1024);
sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
SA_SAMPLE_FORMAT_S16, sample_rate, 1,
program_name, "generate-tones-lut1024-S16-mono");
if ( ! sa_out )
return 0;
generate_test_tones(sa_out, 10);
simpleaudio_close(sa_out);
sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
SA_SAMPLE_FORMAT_FLOAT, sample_rate, 1,
program_name, "generate-tones-lut1024-FLOAT-mono");
if ( ! sa_out )
return 0;
generate_test_tones(sa_out, 10);
simpleaudio_close(sa_out);
// disable the sine wave LUT
simpleaudio_tone_init(0);
sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
SA_SAMPLE_FORMAT_S16, sample_rate, 1,
program_name, "generate-tones-nolut-S16-mono");
if ( ! sa_out )
return 0;
generate_test_tones(sa_out, 10);
simpleaudio_close(sa_out);
sa_out = simpleaudio_open_stream(backend, SA_STREAM_PLAYBACK,
SA_SAMPLE_FORMAT_FLOAT, sample_rate, 1,
program_name, "generate-tones-nolut-FLOAT-mono");
if ( ! sa_out )
return 0;
generate_test_tones(sa_out, 10);
simpleaudio_close(sa_out);
return 1;
}
void
version()
{
printf(
"minimodem %s\n"
"Copyright (C) 2011 Kamal Mostafa <kamal@whence.com>\n"
"License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html>.\n"
"This is free software: you are free to change and redistribute it.\n"
"There is NO WARRANTY, to the extent permitted by law.\n\n"
"Written by Kamal Mostafa <kamal@whence.com>.\n",
VERSION);
}
void
usage()
{
fprintf(stderr,
"usage: minimodem [--tx|--rx] [options] {baudmode}\n"
" -t, --tx, --transmit, --write\n"
" -r, --rx, --receive, --read (default)\n"
" [options]\n"
" -a, --auto-carrier\n"
" -c, --confidence {threshold}\n"
" -8, --ascii ASCII 8-N-1\n"
" -5, --baudot Baudot 5-N-1\n"
" -f, --file {filename.flac}\n"
" -b, --bandwidth {rx_bandwidth}\n"
" -M, --mark {mark_freq}\n"
" -S, --space {space_freq}\n"
" -T, --txstopbits {m.n}\n"
" -q, --quiet\n"
" -R, --samplerate {rate}\n"
" -V, --version\n"
" -A, --alsa\n"
" --lut={tx_sin_table_len}\n"
" --float-samples\n"
" --benchmarks\n"
" {baudmode}\n"
" 1200 Bell202 1200 bps --ascii\n"
" 300 Bell103 300 bps --ascii\n"
" any_number_N Bell103 N bps --ascii\n"
" rtty RTTY 45.45 bps --baudot\n"
);
exit(1);
}
int
main( int argc, char*argv[] )
{
char *modem_mode = NULL;
int TX_mode = -1;
int quiet_mode = 0;
float band_width = 0;
unsigned int bfsk_mark_f = 0;
unsigned int bfsk_space_f = 0;
float bfsk_txstopbits = 0;
unsigned int bfsk_n_data_bits = 0;
int autodetect_shift;
char *filename = NULL;
float carrier_autodetect_threshold = 0.0;
float bfsk_confidence_threshold = 0.6;
sa_backend_t sa_backend = SA_BACKEND_SYSDEFAULT;
sa_format_t sample_format = SA_SAMPLE_FORMAT_S16;
unsigned int sample_rate = 48000;
unsigned int nchannels = 1; // FIXME: only works with one channel
unsigned int tx_sin_table_len = 4096;
/* validate the default system audio mechanism */
#if !(USE_PULSEAUDIO || USE_ALSA)
# define _MINIMODEM_NO_SYSTEM_AUDIO
# if !USE_SNDFILE
# error At least one of {USE_PULSEAUDIO,USE_ALSA,USE_SNDFILE} must be enabled!
# endif
#endif
program_name = strrchr(argv[0], '/');
if ( program_name )
program_name++;
else
program_name = argv[0];
int c;
int option_index;
enum {
MINIMODEM_OPT_UNUSED=256, // placeholder
MINIMODEM_OPT_LUT,
MINIMODEM_OPT_FLOAT_SAMPLES,
MINIMODEM_OPT_BENCHMARKS,
};
while ( 1 ) {
static struct option long_options[] = {
{ "version", 0, 0, 'V' },
{ "tx", 0, 0, 't' },
{ "transmit", 0, 0, 't' },
{ "write", 0, 0, 't' },
{ "rx", 0, 0, 'r' },
{ "receive", 0, 0, 'r' },
{ "read", 0, 0, 'r' },
{ "confidence", 1, 0, 'c' },
{ "auto-carrier", 0, 0, 'a' },
{ "ascii", 0, 0, '8' },
{ "baudot", 0, 0, '5' },
{ "file", 1, 0, 'f' },
{ "bandwidth", 1, 0, 'b' },
{ "mark", 1, 0, 'M' },
{ "space", 1, 0, 'S' },
{ "txstopbits", 1, 0, 'T' },
{ "quiet", 0, 0, 'q' },
{ "alsa", 0, 0, 'A' },
{ "samplerate", 1, 0, 'R' },
{ "lut", 1, 0, MINIMODEM_OPT_LUT },
{ "float-samples", 0, 0, MINIMODEM_OPT_FLOAT_SAMPLES },
{ "benchmarks", 0, 0, MINIMODEM_OPT_BENCHMARKS },
{ 0 }
};
c = getopt_long(argc, argv, "Vtrc:a85f:b:M:S:T:qAR:",
long_options, &option_index);
if ( c == -1 )
break;
switch( c ) {
case 'V':
version();
exit(0);
case 't':
if ( TX_mode == 0 )
usage();
TX_mode = 1;
break;
case 'r':
if ( TX_mode == 1 )
usage();
TX_mode = 0;
break;
case 'c':
bfsk_confidence_threshold = atof(optarg);
break;
case 'a':
carrier_autodetect_threshold = 0.001;
break;
case 'f':
filename = optarg;
break;
case '8':
bfsk_n_data_bits = 8;
break;
case '5':
bfsk_n_data_bits = 5;
break;
case 'b':
band_width = atof(optarg);
assert( band_width != 0 );
break;
case 'M':
bfsk_mark_f = atoi(optarg);
assert( bfsk_mark_f > 0 );
break;
case 'S':
bfsk_space_f = atoi(optarg);
assert( bfsk_space_f > 0 );
break;
case 'T':
bfsk_txstopbits = atof(optarg);
assert( bfsk_txstopbits > 0 );
break;
case 'q':
quiet_mode = 1;
break;
case 'R':
sample_rate = atoi(optarg);
assert( sample_rate > 0 );
break;
case 'A':
#if USE_ALSA
sa_backend = SA_BACKEND_ALSA;
#else
fprintf(stderr, "E: This build of minimodem was configured without alsa support.\n");
exit(1);
#endif
break;
case MINIMODEM_OPT_LUT:
tx_sin_table_len = atoi(optarg);
break;
case MINIMODEM_OPT_FLOAT_SAMPLES:
sample_format = SA_SAMPLE_FORMAT_FLOAT;
break;
case MINIMODEM_OPT_BENCHMARKS:
benchmarks();
exit(0);
break;
default:
usage();
}
}
if ( TX_mode == -1 )
TX_mode = 0;
/* The receive code requires floating point samples to feed to the FFT */
if ( TX_mode == 0 )
sample_format = SA_SAMPLE_FORMAT_FLOAT;
if ( filename ) {
#if !USE_SNDFILE
fprintf(stderr, "E: This build of minimodem was configured without sndfile,\nE: so the --file flag is not supported.\n");
exit(1);
#endif
} else {
#ifdef _MINIMODEM_NO_SYSTEM_AUDIO
fprintf(stderr, "E: this build of minimodem was configured without system audio support,\nE: so only the --file mode is supported.\n");
exit(1);
#endif
}
#if 0
if (optind < argc) {
printf("non-option ARGV-elements: ");
while (optind < argc)
printf("%s ", argv[optind++]);
printf("\n");
}
#endif
if (optind + 1 != argc) {
fprintf(stderr, "E: *** Must specify {baudmode} (try \"300\") ***\n");
usage();
}
modem_mode = argv[optind++];
float bfsk_data_rate = 0.0;
int (*bfsk_framebits_encode)( unsigned int *databits_outp, char char_out );
unsigned int (*bfsk_framebits_decode)( char *dataout_p, unsigned int dataout_size,
unsigned int bits );
if ( strncasecmp(modem_mode, "rtty",5)==0 ) {
bfsk_data_rate = 45.45;
if ( bfsk_n_data_bits == 0 )
bfsk_n_data_bits = 5;
if ( bfsk_txstopbits == 0 )
bfsk_txstopbits = 1.5;
} else {
bfsk_data_rate = atof(modem_mode);
if ( bfsk_n_data_bits == 0 )
bfsk_n_data_bits = 8;
}
if ( bfsk_data_rate == 0.0 )
usage();
if ( bfsk_n_data_bits == 8 ) {
bfsk_framebits_decode = framebits_decode_ascii8;
bfsk_framebits_encode = framebits_encode_ascii8;
} else if ( bfsk_n_data_bits == 5 ) {
bfsk_framebits_decode = framebits_decode_baudot;
bfsk_framebits_encode = framebits_encode_baudot;
} else {
assert( 0 && bfsk_n_data_bits );
}
if ( bfsk_data_rate >= 400 ) {
/*
* Bell 202: baud=1200 mark=1200 space=2200
*/
autodetect_shift = - ( bfsk_data_rate * 5 / 6 );
if ( bfsk_mark_f == 0 )
bfsk_mark_f = bfsk_data_rate / 2 + 600;
if ( bfsk_space_f == 0 )
bfsk_space_f = bfsk_mark_f - autodetect_shift;
if ( band_width == 0 )
band_width = 200;
} else if ( bfsk_data_rate >= 100 ) {
/*
* Bell 103: baud=300 mark=1270 space=1070
* ITU-T V.21: baud=300 mark=1280 space=1080
*/
autodetect_shift = 200;
if ( bfsk_mark_f == 0 )
bfsk_mark_f = 1270;
if ( bfsk_space_f == 0 )
bfsk_space_f = bfsk_mark_f - autodetect_shift;
if ( band_width == 0 )
band_width = 50; // close enough
} else {
/*
* RTTY: baud=45.45 mark/space=variable shift=-170
*/
autodetect_shift = 170;
if ( bfsk_mark_f == 0 )
bfsk_mark_f = 1585;
if ( bfsk_space_f == 0 )
bfsk_space_f = bfsk_mark_f - autodetect_shift;
if ( band_width == 0 ) {
band_width = 10; // FIXME chosen arbitrarily
}
}
if ( bfsk_txstopbits == 0 )
bfsk_txstopbits = 1.0;
/* restrict band_width to <= data rate (FIXME?) */
if ( band_width > bfsk_data_rate )
band_width = bfsk_data_rate;
char *stream_name = NULL;;
if ( filename ) {
sa_backend = SA_BACKEND_FILE;
stream_name = filename;
}
/*
* Handle transmit mode
*/
if ( TX_mode ) {
simpleaudio_tone_init(tx_sin_table_len);
int tx_interactive = 0;
if ( ! stream_name ) {
tx_interactive = 1;
stream_name = "output audio";
}
simpleaudio *sa_out;
sa_out = simpleaudio_open_stream(sa_backend, SA_STREAM_PLAYBACK,
sample_format, sample_rate, nchannels,
program_name, stream_name);
if ( ! sa_out )
return 1;
fsk_transmit_stdin(sa_out, tx_interactive,
bfsk_data_rate,
bfsk_mark_f, bfsk_space_f,
bfsk_n_data_bits,
bfsk_txstopbits,
bfsk_framebits_encode
);
simpleaudio_close(sa_out);
return 0;
}
/*
* Open the input audio stream
*/
if ( ! stream_name )
stream_name = "input audio";
simpleaudio *sa;
sa = simpleaudio_open_stream(sa_backend, SA_STREAM_RECORD,
sample_format, sample_rate, nchannels,
program_name, stream_name);
if ( ! sa )
return 1;
/*
* Prepare the input sample chunk rate
*/
float nsamples_per_bit = sample_rate / bfsk_data_rate;
/*
* Prepare the fsk plan
*/
fsk_plan *fskp;
fskp = fsk_plan_new(sample_rate, bfsk_mark_f, bfsk_space_f,
band_width, bfsk_n_data_bits);
if ( !fskp ) {
fprintf(stderr, "fsk_plan_new() failed\n");
return 1;
}
/*
* Prepare the input sample buffer. For 8-bit frames with prev/start/stop
* we need 11 data-bits worth of samples, and we will scan through one bits
* worth at a time, hence we need a minimum total input buffer size of 12
* data-bits. */
// FIXME I should be able to reduce this to * 9 for 5-bit data, but
// it SOMETIMES crashes -- probably due to non-integer nsamples_per_bit
// FIXME by passing it down into the fsk code?
size_t samplebuf_size = ceilf(nsamples_per_bit) * 12;
float *samplebuf = malloc(samplebuf_size * sizeof(float));
float *samples_readptr = samplebuf;
size_t read_nsamples = samplebuf_size;
size_t samples_nvalid = 0;
debug_log("samplebuf_size=%lu\n", samplebuf_size);
/*
* Run the main loop
*/
int ret = 0;
int carrier = 0;
float confidence_total = 0;
unsigned int nframes_decoded = 0;
size_t carrier_nsamples = 0;
unsigned int noconfidence = 0;
size_t noconfidence_nsamples = 0;
unsigned int advance = 0;
while ( 1 ) {
debug_log("advance=%u\n", advance);
if ( carrier && nframes_decoded > 0 )
carrier_nsamples += advance;
/* Shift the samples in samplebuf by 'advance' samples */
assert( advance <= samplebuf_size );
if ( advance == samplebuf_size ) {
samples_nvalid = 0;
samples_readptr = samplebuf;
read_nsamples = samplebuf_size;
advance = 0;
}
if ( advance ) {
if ( advance > samples_nvalid )
break;
memmove(samplebuf, samplebuf+advance,
(samplebuf_size-advance)*sizeof(float));
samples_nvalid -= advance;
samples_readptr = samplebuf + (samplebuf_size-advance);
read_nsamples = advance;
}
/* Read more samples into samplebuf (fill it) */
assert ( read_nsamples > 0 );
assert ( samples_nvalid + read_nsamples <= samplebuf_size );
ssize_t r;
r = simpleaudio_read(sa, samples_readptr, read_nsamples);
debug_log("simpleaudio_read(samplebuf+%ld, n=%lu) returns %ld\n",
samples_readptr - samplebuf, read_nsamples, r);
if ( r < 0 ) {
fprintf(stderr, "simpleaudio_read: error\n");
ret = -1;
break;
}
else if ( r > 0 )
samples_nvalid += r;
if ( samples_nvalid == 0 )
break;
/* Auto-detect carrier frequency */
static int carrier_band = -1;
if ( carrier_autodetect_threshold > 0.0 && carrier_band < 0 ) {
unsigned int i;
float nsamples_per_scan = nsamples_per_bit;
if ( nsamples_per_scan > fskp->fftsize )
nsamples_per_scan = fskp->fftsize;
for ( i=0; i+nsamples_per_scan<=samples_nvalid;
i+=nsamples_per_scan ) {
carrier_band = fsk_detect_carrier(fskp,
samplebuf+i, nsamples_per_scan,
carrier_autodetect_threshold);
if ( carrier_band >= 0 )
break;
}
advance = i + nsamples_per_scan;
if ( advance > samples_nvalid )
advance = samples_nvalid;
if ( carrier_band < 0 ) {
debug_log("autodetected carrier band not found\n");
continue;
}
// FIXME: hardcoded negative shift
int b_shift = - (float)(autodetect_shift + fskp->band_width/2.0)
/ fskp->band_width;
/* only accept a carrier as b_mark if it will not result
* in a b_space band which is "too low". */
if ( carrier_band + b_shift < 1 ) {
debug_log("autodetected space band too low\n" );
carrier_band = -1;
continue;
}
debug_log("### TONE freq=%.1f ###\n",
carrier_band * fskp->band_width);
fsk_set_tones_by_bandshift(fskp, /*b_mark*/carrier_band, b_shift);
}
/*
* The main processing algorithm: scan samplesbuf for FSK frames,
* looking at an entire frame at once.
*/
debug_log( "--------------------------\n");
unsigned int frame_nsamples = nsamples_per_bit * fskp->n_frame_bits;
if ( samples_nvalid < frame_nsamples )
break;
unsigned int try_max_nsamples = nsamples_per_bit;
#define FSK_ANALYZE_NSTEPS 10 /* accuracy vs. performance */
// Note: FSK_ANALYZE_NSTEPS has subtle effects on the
// "rate perfect" calculation. oh well.
unsigned int try_step_nsamples = nsamples_per_bit / FSK_ANALYZE_NSTEPS;
if ( try_step_nsamples == 0 )
try_step_nsamples = 1;
float confidence;
unsigned int bits = 0;
/* Note: frame_start_sample is actually the sample where the
* prev_stop bit begins (since the "frame" includes the prev_stop). */
unsigned int frame_start_sample = 0;
confidence = fsk_find_frame(fskp, samplebuf, frame_nsamples,
try_max_nsamples,
try_step_nsamples,
&bits,
&frame_start_sample
);
// FIXME: hardcoded chop off framing bits
if ( fskp->n_data_bits == 5 )
bits = ( bits >> 2 ) & 0x1F;
else
bits = ( bits >> 2 ) & 0xFF;
#define FSK_MAX_NOCONFIDENCE_BITS 20
#define FSK_SCAN_LAG 0.2
if ( confidence <= bfsk_confidence_threshold ) {
// FIXME: explain
if ( ++noconfidence > FSK_MAX_NOCONFIDENCE_BITS )
{
carrier_band = -1;
if ( carrier ) {
carrier_nsamples -= noconfidence_nsamples;
if ( nframes_decoded > 0 )
carrier_nsamples += nsamples_per_bit * FSK_SCAN_LAG;
if ( !quiet_mode )
report_no_carrier(fskp, sample_rate, bfsk_data_rate,
nsamples_per_bit, nframes_decoded,
carrier_nsamples, confidence_total);
carrier = 0;
carrier_nsamples = 0;
confidence_total = 0;
nframes_decoded = 0;
}
}
/* Advance the sample stream forward by try_max_nsamples so the
* next time around the loop we continue searching from where
* we left off this time. */
advance = try_max_nsamples;
noconfidence_nsamples += advance;
continue;
}
if ( !carrier ) {
if ( !quiet_mode ) {
if ( bfsk_data_rate >= 100 )
fprintf(stderr, "### CARRIER %u @ %.1f Hz ###\n",
(unsigned int)(bfsk_data_rate + 0.5),
fskp->b_mark * fskp->band_width);
else
fprintf(stderr, "### CARRIER %.2f @ %.1f Hz ###\n",
bfsk_data_rate,
fskp->b_mark * fskp->band_width);
}
carrier = 1;
/* back up carrier_nsamples to account for the imminent advance */
noconfidence_nsamples = frame_start_sample;
bfsk_framebits_decode(0, 0, 0); /* reset the frame processor */
}
confidence_total += confidence;
nframes_decoded++;
noconfidence = 0;
/* Advance the sample stream forward past the decoded frame
* but not past the stop bit, since we want it to appear as
* the prev_stop bit of the next frame, so ...
*
* advance = 1 prev_stop + 1 start + N data bits == n_data_bits+2
*
* but actually advance just a bit less than that to allow
* for clock skew, hence FSK_SCAN_LAG.
*/
advance = frame_start_sample +
nsamples_per_bit * (float)(fskp->n_data_bits + 2 - FSK_SCAN_LAG);
debug_log("@ nsamples_per_bit=%.3f n_data_bits=%u "
" frame_start=%u advance=%u\n",
nsamples_per_bit, fskp->n_data_bits,
frame_start_sample, advance);
/*
* Send the raw data frame bits to the backend frame processor
* for final conversion to output data bytes.
*/
unsigned int dataout_size = 4096;
char dataoutbuf[4096];
unsigned int dataout_nbytes = 0;
dataout_nbytes += bfsk_framebits_decode(dataoutbuf + dataout_nbytes,
dataout_size - dataout_nbytes,
bits);
/*
* Print the output buffer to stdout
*/
if ( dataout_nbytes ) {
char *p = dataoutbuf;
for ( ; dataout_nbytes; p++,dataout_nbytes-- ) {
char printable_char = isprint(*p)||isspace(*p) ? *p : '.';
printf( "%c", printable_char );
}
fflush(stdout);
}
} /* end of the main loop */
if ( carrier ) {
carrier_nsamples -= noconfidence_nsamples;
if ( nframes_decoded > 0 )
carrier_nsamples += nsamples_per_bit * FSK_SCAN_LAG;
if ( !quiet_mode )
report_no_carrier(fskp, sample_rate, bfsk_data_rate,
nsamples_per_bit, nframes_decoded,
carrier_nsamples, confidence_total);
}
simpleaudio_close(sa);
fsk_plan_destroy(fskp);
return ret;
}
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