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fsk_bit_analyze refactor

This commit is contained in:
Kamal Mostafa 2011-06-04 15:55:22 -07:00
parent 0e888d2bf2
commit 1e96d42d16
1 changed files with 26 additions and 30 deletions
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48
src/fsk.c
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@ -134,20 +134,21 @@ band_mag( fftwf_complex * const cplx, unsigned int band, float scalar )
static void
fsk_bit_analyze( fsk_plan *fskp, float *samples, unsigned int bit_nsamples,
float *mag_mark_outp, float *mag_space_outp)
unsigned int *bit_outp, float *bit_strength_outp)
{
unsigned int pa_nchannels = 1;
bzero(fskp->fftin, (fskp->fftsize * sizeof(float) * pa_nchannels));
memcpy(fskp->fftin, samples, bit_nsamples * sizeof(float));
fftwf_execute(fskp->fftplan);
float magscalar = 1.0 / ((float)bit_nsamples/2.0);
*mag_mark_outp = band_mag(fskp->fftout, fskp->b_mark, magscalar);
*mag_space_outp = band_mag(fskp->fftout, fskp->b_space, magscalar);
debug_log( "\t%.2f %.2f %s sig=%.2f\n",
float mag_mark = band_mag(fskp->fftout, fskp->b_mark, magscalar);
float mag_space = band_mag(fskp->fftout, fskp->b_space, magscalar);
*bit_outp = mag_mark > mag_space ? 1 : 0; // mark==1, space==0
*bit_strength_outp = fabs(mag_mark - mag_space);
debug_log( "\t%.2f %.2f %s bit=%u bit_strength=%.2f\n",
*mag_mark_outp, *mag_space_outp,
*mag_mark_outp > *mag_space_outp ? "mark " : " space",
fabs(*mag_mark_outp - *mag_space_outp)
);
*bit_outp, *bit_strength_outp);
}
@ -168,9 +169,9 @@ fsk_frame_decode( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
// p == stop bit
// MSddddddddM <-- expected mark/space framing pattern
unsigned int begin_i_idlebit = 0;
unsigned int begin_s_startbit = (float)(samples_per_bit * 1 + 0.5);
unsigned int begin_p_stopbit = (float)(samples_per_bit * 10 + 0.5);
unsigned int begin_idlebit = 0;
unsigned int begin_startbit = (float)(samples_per_bit * 1 + 0.5);
unsigned int begin_stopbit = (float)(samples_per_bit * 10 + 0.5);
/*
* To optimize performance for a streaming scenario, check start bit first,
@ -179,23 +180,20 @@ fsk_frame_decode( fsk_plan *fskp, float *samples, unsigned int frame_nsamples,
* collect the n_data_bits
*/
float sM, sS, pM, pS, iM, iS;
float s_str, p_str, i_str, d_str;
unsigned int bit;
debug_log("\t\tstart ");
fsk_bit_analyze(fskp, samples+begin_s_startbit, bit_nsamples, &sM, &sS);
bit = sM > sS;
fsk_bit_analyze(fskp, samples+begin_startbit, bit_nsamples, &bit, &s_str);
if ( bit != 0 )
return 0.0;
v += sS - sM;
v += s_str;
debug_log("\t\tstop ");
fsk_bit_analyze(fskp, samples+begin_p_stopbit, bit_nsamples, &pM, &pS);
bit = pM > pS;
fsk_bit_analyze(fskp, samples+begin_stopbit, bit_nsamples, &bit, &p_str);
if ( bit != 1 )
return 0.0;
v += pM - pS;
v += p_str;
#define AVOID_TRANSIENTS 0.7
#ifdef AVOID_TRANSIENTS
@ -203,26 +201,24 @@ debug_log("\t\tstop ");
* a transient as a start bit, as often results in a single false
* character when the mark "leader" tone begins. Require that the
* diff between start bit and stop bit strength not be "large". */
if ( fabs((sS-sM)-(pM-pS)) > fabs(sS-sM) * AVOID_TRANSIENTS )
if ( fabs(s_str-p_str) > (s_str * AVOID_TRANSIENTS) )
return 0.0;
#endif
debug_log("\t\tidle ");
fsk_bit_analyze(fskp, samples+begin_i_idlebit, bit_nsamples, &iM, &iS);
bit = iM > iS;
fsk_bit_analyze(fskp, samples+begin_idlebit, bit_nsamples, &bit, &i_str);
if ( bit != 1 )
return 0.0;
v += iM - iS;
v += i_str;
unsigned int bits_out = 0;
int i;
for ( i=0; i<fskp->n_data_bits; i++ ) {
unsigned int begin = (float)(samples_per_bit * (i+2) + 0.5);
float dM, dS;
debug_log("\t\tdata ");
fsk_bit_analyze(fskp, samples+begin, bit_nsamples, &dM, &dS);
bit = dM > dS;
v += fabs(dM - dS);
unsigned int begin_databit = (float)(samples_per_bit * (i+2) + 0.5);
fsk_bit_analyze(fskp, samples+begin_databit, bit_nsamples,
&bit, &d_str);
v += d_str;
bits_out |= bit << i;
}
*bits_outp = bits_out;