@@ -226,6 +226,8 @@ struct demodulator_state_s
226226 signed int data_clock_pll ; // PLL for data clock recovery.
227227 // It is incremented by pll_step_per_sample
228228 // for each audio sample.
229+ // Must be 32 bits!!!
230+ // So far, this is the case for every compiler used.
229231
230232 signed int prev_d_c_pll ; // Previous value of above, before
231233 // incrementing, to detect overflows.
@@ -238,6 +240,18 @@ struct demodulator_state_s
238240
239241 int lfsr ; // Descrambler shift register.
240242
243+ // This is for detecting phase lock to incoming signal.
244+
245+ int good_flag ; // Set if transition is near where expected,
246+ // i.e. at a good time.
247+ int bad_flag ; // Set if transition is not where expected,
248+ // i.e. at a bad time.
249+ unsigned char good_hist ; // History of good transitions for past octet.
250+ unsigned char bad_hist ; // History of bad transitions for past octet.
251+ unsigned int score ; // History of whether good triumphs over bad
252+ // for past 32 symbols.
253+ int data_detect ; // True when locked on to signal.
254+
241255 } slicer [MAX_SLICERS ]; // Actual number in use is num_slicers.
242256 // Should be in range 1 .. MAX_SLICERS,
243257/*
@@ -336,5 +350,100 @@ struct demodulator_state_s
336350
337351};
338352
353+
354+ /*-------------------------------------------------------------------
355+ *
356+ * Name: pll_dcd_signal_transition2
357+ * dcd_each_symbol2
358+ *
359+ * Purpose: New DCD strategy for 1.6.
360+ *
361+ * Inputs: D Pointer to demodulator state.
362+ *
363+ * chan Radio channel: 0 to MAX_CHANS - 1
364+ *
365+ * subchan Which of multiple demodulators: 0 to MAX_SUBCHANS - 1
366+ *
367+ * slice Slicer number: 0 to MAX_SLICERS - 1.
368+ *
369+ * dpll_phase Signed 32 bit counter for DPLL phase.
370+ * Wraparound is where data is sampled.
371+ * Ideally transitions would occur close to 0.
372+ *
373+ * Output: D->slicer[slice].data_detect - true when PLL is locked to incoming signal.
374+ *
375+ * Description: From the beginning, DCD was based on finding several flag octets
376+ * in a row and dropping when eight bits with no transitions.
377+ * It was less than ideal but we limped along with it all these years.
378+ * This fell apart when FX.25 came along and a couple of the
379+ * correlation tags have eight "1" bits in a row.
380+ *
381+ * Our new strategy is to keep a running score of how well demodulator
382+ * output transitions match to where expected.
383+ *
384+ *--------------------------------------------------------------------*/
385+
386+ #include "hdlc_rec.h" // for dcd_change
387+
388+ // These are good for 1200 bps AFSK.
389+ // Might want to override for other modems.
390+
391+ #ifndef DCD_THRESH_ON
392+ #define DCD_THRESH_ON 30 // Hysteresis: Can miss 2 out of 32 for detecting lock.
393+ // 31 is best for TNC Test CD. 30 almost as good.
394+ // 30 better for 1200 regression test.
395+ #endif
396+
397+ #ifndef DCD_THRESH_OFF
398+ #define DCD_THRESH_OFF 6 // Might want a little more fine tuning.
399+ #endif
400+
401+ #ifndef DCD_GOOD_WIDTH
402+ #define DCD_GOOD_WIDTH 512 // No more than 1024!!!
403+ #endif
404+
405+ __attribute__((always_inline ))
406+ inline static void pll_dcd_signal_transition2 (struct demodulator_state_s * D , int slice , int dpll_phase )
407+ {
408+ if (dpll_phase > - DCD_GOOD_WIDTH * 1024 * 1024 && dpll_phase < DCD_GOOD_WIDTH * 1024 * 1024 ) {
409+ D -> slicer [slice ].good_flag = 1 ;
410+ }
411+ else {
412+ D -> slicer [slice ].bad_flag = 1 ;
413+ }
414+ }
415+
416+ __attribute__((always_inline ))
417+ inline static void pll_dcd_each_symbol2 (struct demodulator_state_s * D , int chan , int subchan , int slice )
418+ {
419+ D -> slicer [slice ].good_hist <<= 1 ;
420+ D -> slicer [slice ].good_hist |= D -> slicer [slice ].good_flag ;
421+ D -> slicer [slice ].good_flag = 0 ;
422+
423+ D -> slicer [slice ].bad_hist <<= 1 ;
424+ D -> slicer [slice ].bad_hist |= D -> slicer [slice ].bad_flag ;
425+ D -> slicer [slice ].bad_flag = 0 ;
426+
427+ D -> slicer [slice ].score <<= 1 ;
428+ // 2 is to detect 'flag' patterns with 2 transitions per octet.
429+ D -> slicer [slice ].score |= (signed )__builtin_popcount (D -> slicer [slice ].good_hist )
430+ - (signed )__builtin_popcount (D -> slicer [slice ].bad_hist ) >= 2 ;
431+
432+ int s = __builtin_popcount (D -> slicer [slice ].score );
433+ if (s >= DCD_THRESH_ON ) {
434+ if (D -> slicer [slice ].data_detect == 0 ) {
435+ D -> slicer [slice ].data_detect = 1 ;
436+ dcd_change (chan , subchan , slice , D -> slicer [slice ].data_detect );
437+ }
438+ }
439+ else if (s <= DCD_THRESH_OFF ) {
440+ if (D -> slicer [slice ].data_detect != 0 ) {
441+ D -> slicer [slice ].data_detect = 0 ;
442+ dcd_change (chan , subchan , slice , D -> slicer [slice ].data_detect );
443+ }
444+ }
445+ }
446+
447+
339448#define FSK_DEMOD_STATE_H 1
340- #endif
449+ #endif
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