fsk expect_bits
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Kamal Mostafa
parent
613f4ec5bd
commit
fd0546d80d
140
src/fsk.c
140
src/fsk.c
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@ -24,6 +24,7 @@
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#include <errno.h>
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#include <stdio.h>
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#include <ctype.h>
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#include <assert.h>
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#include "fsk.h"
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@ -136,37 +137,20 @@ fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
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}
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/* returns confidence value [0.0 to 1.0] */
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static void
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fsk_bits_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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unsigned int *bits_outp, float *bit_strengths_outp )
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{
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unsigned int bit_nsamples = (float)(samples_per_bit + 0.5);
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unsigned int nbits = fskp->n_data_bits;
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unsigned int bits_out = 0;
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int i;
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for ( i=0; i<nbits; i++ ) {
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unsigned int begin_databit = (float)(samples_per_bit * i + 0.5);
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unsigned int bit;
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debug_log("\t\tdata begin_data_bit=%u ", begin_databit);
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fsk_bit_analyze(fskp, samples+begin_databit, bit_nsamples,
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&bit, &bit_strengths_outp[i]);
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bits_out |= bit << i;
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}
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*bits_outp = bits_out;
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}
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/* returns confidence value [0.0 to 1.0] */
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static float
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fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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unsigned int *bits_outp )
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{
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float v = 0;
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unsigned int bit_nsamples = (float)(samples_per_bit + 0.5);
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int n_bits = fskp->n_frame_bits;
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// char *expect_bit_string = "10dddddddd1";
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char expect_bit_string[32];
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memset(expect_bit_string, 'd', 32);
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expect_bit_string[0] = '1';
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expect_bit_string[1] = '0';
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expect_bit_string[fskp->n_data_bits + 2] = '1';
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// example...
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// 0123456789A
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// isddddddddp i == idle bit (a.k.a. prev_stop bit)
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// s == start bit
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@ -174,32 +158,37 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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// p == stop bit
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// MSddddddddM <-- expected mark/space framing pattern
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unsigned int begin_idlebit = 0;
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unsigned int begin_startbit = (float)(samples_per_bit * 1 + 0.5);
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unsigned int begin_databits = (float)(samples_per_bit * 2 + 0.5);
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unsigned int begin_stopbit = (float)(samples_per_bit * (fskp->n_data_bits+2) + 0.5);
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unsigned int bit_nsamples = (float)(samples_per_bit + 0.5);
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/*
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* To optimize performance for a streaming scenario, check start bit first,
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* then stop, then idle bits... we're "searching" for start, must validate
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* stop, and finally we want to to collect idle's v value. After all that
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* collect the n_data_bits
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*/
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unsigned int bit_values[32];
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float bit_strengths[32];
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unsigned int bit_begin_sample;
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int bitnum;
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float s_str, p_str, i_str;
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unsigned int bit;
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float v = 0;
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debug_log("\t\tstart ");
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fsk_bit_analyze(fskp, samples+begin_startbit, bit_nsamples, &bit, &s_str);
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if ( bit != 0 )
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return 0.0;
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v += s_str;
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char *expect_bits = expect_bit_string;
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debug_log("\t\tstop ");
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fsk_bit_analyze(fskp, samples+begin_stopbit, bit_nsamples, &bit, &p_str);
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if ( bit != 1 )
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return 0.0;
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v += p_str;
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/* pass #1 - process and check only the "required" (1/0) expect_bits */
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for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
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if ( expect_bits[bitnum] == 'd' )
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continue;
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assert( expect_bits[bitnum] == '1' || expect_bits[bitnum] == '0' );
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bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5);
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debug_log( " bit# %2u @ %u: ", bitnum, bit_begin_sample);
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fsk_bit_analyze(fskp, samples+bit_begin_sample, bit_nsamples,
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&bit_values[bitnum], &bit_strengths[bitnum]);
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if ( (expect_bits[bitnum] - '0') != bit_values[bitnum] )
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return 0.0; /* does not match expected; abort frame analysis. */
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v += bit_strengths[bitnum];
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}
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// float i_str = bit_strengths[0];
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float s_str = bit_strengths[1];
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float p_str = bit_strengths[fskp->n_data_bits + 2];
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#define AVOID_TRANSIENTS 0.7
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#ifdef AVOID_TRANSIENTS
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@ -208,32 +197,31 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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* character when the mark "leader" tone begins. Require that the
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* diff between start bit and stop bit strength not be "large". */
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if ( fabs(s_str-p_str) > (s_str * AVOID_TRANSIENTS) ) {
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debug_log("avoid_transient\n");
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debug_log(" avoid transient\n");
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return 0.0;
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}
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#endif
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debug_log("\t\tidle ");
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fsk_bit_analyze(fskp, samples+begin_idlebit, bit_nsamples, &bit, &i_str);
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if ( bit != 1 )
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return 0.0;
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v += i_str;
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/* pass #2 - process only the dontcare ('d') expect_bits */
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for ( bitnum=0; bitnum<n_bits; bitnum++ ) {
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if ( expect_bits[bitnum] != 'd' )
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continue;
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bit_begin_sample = (float)(samples_per_bit * bitnum + 0.5);
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debug_log( " bit# %2u @ %u: ", bitnum, bit_begin_sample);
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fsk_bit_analyze(fskp, samples+bit_begin_sample, bit_nsamples,
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&bit_values[bitnum], &bit_strengths[bitnum]);
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v += bit_strengths[bitnum];
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}
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// Analyze the actual data payload bits
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float databit_strengths[32];
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fsk_bits_analyze(fskp, samples+begin_databits, samples_per_bit,
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bits_outp, databit_strengths);
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// compute average bit strength 'v'
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int i;
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for ( i=0; i<fskp->n_data_bits; i++ )
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v += databit_strengths[i];
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v /= (fskp->n_data_bits + 3);
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/* compute average bit strength 'v' */
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v /= n_bits;
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#define FSK_MIN_STRENGTH 0.005
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if ( v < FSK_MIN_STRENGTH )
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return 0.0;
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int i;
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#define CONFIDENCE_ALGO 2
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#if ( CONFIDENCE_ALGO == 1 )
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@ -249,15 +237,19 @@ fsk_frame_analyze( fsk_plan *fskp, float *samples, float samples_per_bit,
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#elif ( CONFIDENCE_ALGO == 2 )
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float confidence = 0;
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confidence += i_str;
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confidence += s_str;
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confidence += p_str;
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for ( i=0; i<fskp->n_data_bits; i++ )
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confidence += databit_strengths[i];
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confidence /= (fskp->n_data_bits + 3);
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for ( i=0; i<n_bits; i++ )
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confidence += bit_strengths[i];
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confidence /= n_bits;
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#endif
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*bits_outp = 0;
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// FIXME: databits at hardcoded offset of +2
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// for ( i=0; i<fskp->n_data_bits; i++ )
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// *bits_outp |= bit_values[i+2] << i;
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for ( i=0; i<n_bits; i++ )
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*bits_outp |= bit_values[i] << i;
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debug_log(" frame confidence (algo #%u) = %f\n",
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CONFIDENCE_ALGO, confidence);
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return confidence;
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@ -296,16 +288,18 @@ fsk_find_frame( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
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float confidence = best_c;
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// FIXME? hardcoded chop off framing bits for debug
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#ifdef FSK_DEBUG
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unsigned char bitchar = ( best_bits >> 2 ) & 0xFF;
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debug_log("FSK_FRAME datum='%c' (0x%02x) c=%f t=%d\n",
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isprint(best_bits)||isspace(best_bits) ? best_bits : '.',
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best_bits,
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isprint(bitchar)||isspace(bitchar) ? bitchar : '.',
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bitchar,
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confidence, best_t);
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#endif
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return confidence;
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}
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#include <assert.h> // FIXME
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// #define FSK_AUTODETECT_MIN_FREQ 600
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// #define FSK_AUTODETECT_MAX_FREQ 5000
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@ -595,6 +595,12 @@ main( int argc, char*argv[] )
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&frame_start_sample
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);
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// FIXME: hardcoded chop off framing bits
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if ( fskp->n_data_bits == 5 )
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bits = ( bits >> 2 ) & 0x1F;
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else
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bits = ( bits >> 2 ) & 0xFF;
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#define FSK_MIN_CONFIDENCE 0.05
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#define FSK_MAX_NOCONFIDENCE_BITS 20
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