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minimodem: fsk_frame_overscan replaces FSK_SCAN_LAG

This commit is contained in:
Kamal Mostafa 2012-08-16 01:03:54 -07:00
parent 6ee10626c9
commit df80c98e22
1 changed files with 33 additions and 9 deletions
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42
src/minimodem.c
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@ -690,7 +690,8 @@ main( int argc, char*argv[] )
// 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;
// FIXME EXPLAIN +1 goes with extra bit when scanning
size_t samplebuf_size = ceilf(nsamples_per_bit) * (12+1);
float *samplebuf = malloc(samplebuf_size * sizeof(float));
float *samples_readptr = samplebuf;
size_t read_nsamples = samplebuf_size;
@ -712,6 +713,25 @@ main( int argc, char*argv[] )
size_t noconfidence_nsamples = 0;
unsigned int advance = 0;
// Fraction of nsamples_per_bit that we will "overscan"; range (0.0 .. 1.0)
float fsk_frame_overscan = 0.5;
// should be != 0.0 (only the nyquist edge cases actually require this?)
// for handling of slightly faster-than-us rates:
// should be >> 0.0 to allow us to lag back for faster-than-us rates
// should be << 1.0 or we may lag backwards over whole bits
// for optimal analysis:
// should be >= 0.5 (half a bit width) or we may not find the optimal bit
// should be < 1.0 (a full bit width) or we may skip over whole bits
assert( fsk_frame_overscan >= 0.0 && fsk_frame_overscan < 1.0 );
// ensure that we overscan at least a single sample
unsigned int nsamples_overscan
= nsamples_per_bit * fsk_frame_overscan + 0.5;
if ( fsk_frame_overscan > 0.0 && nsamples_overscan == 0 )
nsamples_overscan = 1;
debug_log("fsk_frame_overscan=%f nsamples_overscan=%u\n",
fsk_frame_overscan, nsamples_overscan);
while ( 1 ) {
debug_log("advance=%u\n", advance);
@ -807,7 +827,12 @@ main( int argc, char*argv[] )
if ( samples_nvalid < frame_nsamples )
break;
unsigned int try_max_nsamples = nsamples_per_bit;
// try_max_nsamples = nsamples_per_bit + nsamples_overscan;
// serves two purposes
// 1. avoids finding a non-optimal first frame
// 2. allows us to track slightly slow signals
unsigned int try_max_nsamples = nsamples_per_bit + nsamples_overscan;
#define FSK_ANALYZE_NSTEPS 10 /* accuracy vs. performance */
// Note: FSK_ANALYZE_NSTEPS has subtle effects on the
// "rate perfect" calculation. oh well.
@ -836,8 +861,6 @@ main( int argc, char*argv[] )
#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 )
@ -846,7 +869,7 @@ main( int argc, char*argv[] )
if ( carrier ) {
carrier_nsamples -= noconfidence_nsamples;
if ( nframes_decoded > 0 )
carrier_nsamples += nsamples_per_bit * FSK_SCAN_LAG;
carrier_nsamples += nsamples_overscan;
if ( !quiet_mode )
report_no_carrier(fskp, sample_rate, bfsk_data_rate,
nsamples_per_bit, nframes_decoded,
@ -895,10 +918,11 @@ main( int argc, char*argv[] )
* 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.
* for tracking slightly fast signals, hence - nsamples_overscan.
*/
advance = frame_start_sample +
nsamples_per_bit * (float)(fskp->n_data_bits + 2 - FSK_SCAN_LAG);
advance = frame_start_sample
+ nsamples_per_bit * (float)(fskp->n_data_bits + 2)
- nsamples_overscan;
debug_log("@ nsamples_per_bit=%.3f n_data_bits=%u "
" frame_start=%u advance=%u\n",
@ -936,7 +960,7 @@ main( int argc, char*argv[] )
if ( carrier ) {
carrier_nsamples -= noconfidence_nsamples;
if ( nframes_decoded > 0 )
carrier_nsamples += nsamples_per_bit * FSK_SCAN_LAG;
carrier_nsamples += nsamples_overscan;
if ( !quiet_mode )
report_no_carrier(fskp, sample_rate, bfsk_data_rate,
nsamples_per_bit, nframes_decoded,