Issue 271 - DCD dropping at wrong time.

Author: wb2osz

src/atest.c

@@ -82,7 +82,7 @@
 #include "ptt.h"
 #include "dtime_now.h"
 #include "fx25.h"
-
+#include "hdlc_rec.h"
 
 
 #if 0	/* Typical but not flexible enough. */
@@ -188,6 +188,9 @@ static int J_opt = 0;			/* 2400 bps PSK compatible MFJ-2400 and maybe others. */
 static int h_opt = 0;			// Hexadecimal display of received packet.
 static char P_opt[16] = "";		// Demodulator profiles.
 static int d_x_opt = 1;			// FX.25 debug.
+static int d_o_opt = 0;			// "-d o" option for DCD output control. */	
+static int dcd_count = 0;
+static int dcd_missing_errors = 0;
 
 
 int main (int argc, char *argv[])
@@ -382,6 +385,7 @@ int main (int argc, char *argv[])
 	       for (char *p=optarg; *p!='\0'; p++) {
 	        switch (*p) {
 	           case 'x':  d_x_opt++; break;			// FX.25
+	           case 'o':  d_o_opt++; break;			// DCD output control
 	           default: break;
 	        }
 	       }
@@ -686,6 +690,10 @@ int main (int argc, char *argv[])
 	elapsed = dtime_now() - start_time;
 
 	dw_printf ("%d packets decoded in %.3f seconds.  %.1f x realtime\n", packets_decoded_total, elapsed, total_filetime/elapsed);
+	if (d_o_opt) {
+	  dw_printf ("DCD count = %d\n", dcd_count);
+	  dw_printf ("DCD missing erors = %d\n", dcd_missing_errors);
+	}
 
 	if (error_if_less_than != -1 && packets_decoded_total < error_if_less_than) {
 	  text_color_set(DW_COLOR_ERROR);
@@ -744,6 +752,7 @@ void dlq_rec_frame (int chan, int subchan, int slice, packet_t pp, alevel_t alev
 	char alevel_text[AX25_ALEVEL_TO_TEXT_SIZE];
 
 	packets_decoded_one++;
+	if ( ! hdlc_rec_data_detect_any(chan)) dcd_missing_errors++;
 
 	ax25_format_addrs (pp, stemp);
 
@@ -777,7 +786,7 @@ void dlq_rec_frame (int chan, int subchan, int slice, packet_t pp, alevel_t alev
 	int min = (int)(sec / 60.);
 	sec -= min * 60;
 
-	dw_printf ("%d:%07.4f ", min, sec);
+	dw_printf ("%d:%06.3f ", min, sec);
 
 	if (h != AX25_SOURCE) {
 	  dw_printf ("Digipeater ");
@@ -876,6 +885,38 @@ void dlq_rec_frame (int chan, int subchan, int slice, packet_t pp, alevel_t alev
 
 void ptt_set (int ot, int chan, int ptt_signal)
 {
+	// Should only get here for DCD output control.
+	static double dcd_start_time[MAX_CHANS];
+
+	if (d_o_opt) {
+	  double t = (double)sample_number / my_audio_config.adev[0].samples_per_sec;
+	  double sec1, sec2;
+	  int min1, min2;
+
+	  text_color_set(DW_COLOR_INFO);
+
+	  if (ptt_signal) {
+	    //sec1 = t;
+	    //min1 = (int)(sec1 / 60.);
+	    //sec1 -= min1 * 60;
+	    //dw_printf ("DCD[%d] = ON    %d:%06.3f\n",  chan, min1, sec1);
+	    dcd_count++;
+	    dcd_start_time[chan] = t;
+	  }
+	  else {
+	    //dw_printf ("DCD[%d] = off   %d:%06.3f   %3.0f\n",  chan, min, sec, (t - dcd_start_time[chan]) * 1000.);
+
+	    sec1 = dcd_start_time[chan];
+	    min1 = (int)(sec1 / 60.);
+	    sec1 -= min1 * 60;
+
+	    sec2 = t;
+	    min2 = (int)(sec2 / 60.);
+	    sec2 -= min2 * 60;
+
+	    dw_printf ("DCD[%d]  %d:%06.3f - %d:%06.3f =  %3.0f\n",  chan, min1, sec1, min2, sec2, (t - dcd_start_time[chan]) * 1000.);
+	  }
+	}
 	return;
 }
 

src/demod_9600.c

@@ -44,14 +44,24 @@
 #include <assert.h>
 #include <ctype.h>
 
+// Fine tuning for different demodulator types.
+
+#define DCD_THRESH_ON 32		// Hysteresis: Can miss 0 out of 32 for detecting lock.
+					// This is best for actual on-the-air signals.
+					// Still too many brief false matches.
+#define DCD_THRESH_OFF 8		// Might want a little more fine tuning.
+#define DCD_GOOD_WIDTH 1024		// No more than 1024!!!
+#include "fsk_demod_state.h"		// Values above override defaults.
+
 #include "tune.h"
-#include "fsk_demod_state.h"
 #include "hdlc_rec.h"
 #include "demod_9600.h"
 #include "textcolor.h"
 #include "dsp.h"
 
 
+
+
 static float slice_point[MAX_SUBCHANS];
 
 
@@ -407,7 +417,7 @@ void demod_9600_process_sample (int chan, int sam, struct demodulator_state_s *D
 	if (chan == 0) {
 
 	  if (1) {
-	  //if (hdlc_rec_gathering (chan, subchan, slice)) {
+	  //if (D->slicer[slice].data_detect) {
 	    char fname[30];
 	    int slice = 0;
 
@@ -516,6 +526,7 @@ inline static void nudge_pll (int chan, int subchan, int slice, float demod_out_
 	  /* Overflow.  Was large positive, wrapped around, now large negative. */
 
 	  hdlc_rec_bit (chan, subchan, slice, demod_out_f > 0, D->modem_type == MODEM_SCRAMBLE, D->slicer[slice].lfsr);
+	  pll_dcd_each_symbol2 (D, chan, subchan, slice);
 	}
 
 /*
@@ -526,11 +537,11 @@ inline static void nudge_pll (int chan, int subchan, int slice, float demod_out_
 
 	  // Note:  Test for this demodulator, not overall for channel.
 
-	  float target = 0;
+	  pll_dcd_signal_transition2 (D, slice, D->slicer[slice].data_clock_pll);
 
-	  target = D->pll_step_per_sample * demod_out_f / (demod_out_f - D->slicer[slice].prev_demod_out_f);
+	  float target = D->pll_step_per_sample * demod_out_f / (demod_out_f - D->slicer[slice].prev_demod_out_f);
 
-	  if (hdlc_rec_gathering (chan, subchan, slice)) {
+	  if (D->slicer[slice].data_detect) {
 	    D->slicer[slice].data_clock_pll = (int)(D->slicer[slice].data_clock_pll * D->pll_locked_inertia + target * (1.0f - D->pll_locked_inertia) );
 	  }
 	  else {
@@ -542,7 +553,7 @@ inline static void nudge_pll (int chan, int subchan, int slice, float demod_out_
 #if DEBUG5
 
 	//if (chan == 0) {
-	if (hdlc_rec_gathering (chan,subchan,slice)) {
+	if (D->slicer[slice].data_detect) {
 
 	  char fname[30];
 

src/demod_afsk.c

@@ -762,7 +762,7 @@ void demod_afsk_process_sample (int chan, int subchan, int sam, struct demodulat
 #if DEBUG4
 
 	if (chan == 0) {
-	if (hdlc_rec_gathering (chan, subchan)) {
+	if (D->slicer[slice].data_detect) {
 	  char fname[30];
 
 
@@ -839,16 +839,18 @@ inline static void nudge_pll (int chan, int subchan, int slice, int demod_data,
 
 	if (D->slicer[slice].data_clock_pll < 0 && D->slicer[slice].prev_d_c_pll > 0) {
 
-	  /* Overflow. */
+	  /* Overflow - this is where we sample. */
 	  hdlc_rec_bit (chan, subchan, slice, demod_data, 0, -1);
+	  pll_dcd_each_symbol2 (D, chan, subchan, slice);
 	}
 
-	// Even if we used alternative method to extract the data bit,
-	//  we still use the low pass output for the PLL.
+	// Transitions nudge the DPLL phase toward the incoming signal.
 
         if (demod_data != D->slicer[slice].prev_demod_data) {
 
-	  if (hdlc_rec_gathering (chan, subchan, slice)) {
+	  pll_dcd_signal_transition2 (D, slice, D->slicer[slice].data_clock_pll);
+
+	  if (D->slicer[slice].data_detect) {
 	    D->slicer[slice].data_clock_pll = (int)(D->slicer[slice].data_clock_pll * D->pll_locked_inertia);
 	  }
 	  else {

src/demod_psk.c

@@ -86,16 +86,25 @@
 #include <assert.h>
 #include <ctype.h>
 
+// Fine tuning for different demodulator types.
+
+#define DCD_THRESH_ON 30		// Hysteresis: Can miss 2 out of 32 for detecting lock.
+#define DCD_THRESH_OFF 6		// Might want a little more fine tuning.
+#define DCD_GOOD_WIDTH 512
+#include "fsk_demod_state.h"		// Values above override defaults.
 
 #include "audio.h"
 #include "tune.h"
-#include "fsk_demod_state.h"
 #include "fsk_gen_filter.h"
 #include "hdlc_rec.h"
 #include "textcolor.h"
 #include "demod_psk.h"
 #include "dsp.h"
 
+
+
+
+
 static const int phase_to_gray_v26[4] = {0, 1, 3, 2};	
 static const int phase_to_gray_v27[8] = {1, 0, 2, 3, 7, 6, 4, 5};	
 
@@ -800,6 +809,7 @@ static void nudge_pll (int chan, int subchan, int slice, int demod_bits, struct
 	    hdlc_rec_bit (chan, subchan, slice, (gray >> 1) & 1, 0, bit_quality[1]);
 	    hdlc_rec_bit (chan, subchan, slice, gray & 1, 0, bit_quality[0]);
 	  }
+	  pll_dcd_each_symbol2 (D, chan, subchan, slice);
 	}
 
 /*
@@ -813,7 +823,9 @@ static void nudge_pll (int chan, int subchan, int slice, int demod_bits, struct
 
         if (demod_bits != D->slicer[slice].prev_demod_data) {
 
-	  if (hdlc_rec_gathering (chan, subchan, slice)) {
+	  pll_dcd_signal_transition2 (D, slice, D->slicer[slice].data_clock_pll);
+
+	  if (D->slicer[slice].data_detect) {
 	    D->slicer[slice].data_clock_pll = (int)floorf((float)(D->slicer[slice].data_clock_pll) * D->pll_locked_inertia);
 	  }
 	  else {

src/fsk_demod_state.h

@@ -226,6 +226,8 @@ struct demodulator_state_s
 		signed int data_clock_pll;		// PLL for data clock recovery.
 							// It is incremented by pll_step_per_sample
 							// for each audio sample.
+							// Must be 32 bits!!!
+							// So far, this is the case for every compiler used.
 
 		signed int prev_d_c_pll;		// Previous value of above, before
 							// incrementing, to detect overflows.
@@ -238,6 +240,18 @@ struct demodulator_state_s
 
 		int lfsr;				// Descrambler shift register.
 
+		// This is for detecting phase lock to incoming signal.
+
+		int good_flag;				// Set if transition is near where expected,
+							// i.e. at a good time.
+		int bad_flag;				// Set if transition is not where expected,
+							// i.e. at a bad time.
+		unsigned char good_hist;		// History of good transitions for past octet.
+		unsigned char bad_hist;			// History of bad transitions for past octet.
+		unsigned int score;			// History of whether good triumphs over bad
+							// for past 32 symbols.
+		int data_detect;			// True when locked on to signal.
+		
 	} slicer [MAX_SLICERS];				// Actual number in use is num_slicers.
 							// Should be in range 1 .. MAX_SLICERS,
 /*
@@ -336,5 +350,100 @@ struct demodulator_state_s
 
 };
 
+
+/*-------------------------------------------------------------------
+ *
+ * Name:        pll_dcd_signal_transition2
+ *		dcd_each_symbol2
+ *
+ * Purpose:     New DCD strategy for 1.6.
+ *
+ * Inputs:	D		Pointer to demodulator state.
+ *
+ *		chan		Radio channel: 0 to MAX_CHANS - 1	
+ *
+ *		subchan		Which of multiple demodulators: 0 to MAX_SUBCHANS - 1
+ *
+ *		slice		Slicer number: 0 to MAX_SLICERS - 1.
+ *
+ *		dpll_phase	Signed 32 bit counter for DPLL phase.
+ *				Wraparound is where data is sampled.
+ *				Ideally transitions would occur close to 0.
+ *				
+ * Output:	D->slicer[slice].data_detect - true when PLL is locked to incoming signal.
+ *
+ * Description:	From the beginning, DCD was based on finding several flag octets
+ *		in a row and dropping when eight bits with no transitions.
+ *		It was less than ideal but we limped along with it all these years.
+ *		This fell apart when FX.25 came along and a couple of the
+ *		correlation tags have eight "1" bits in a row.
+ *
+ * 		Our new strategy is to keep a running score of how well demodulator
+ *		output transitions match to where expected.
+ *
+ *--------------------------------------------------------------------*/
+
+#include "hdlc_rec.h"        // for dcd_change
+
+// These are good for 1200 bps AFSK.
+// Might want to override for other modems.
+
+#ifndef DCD_THRESH_ON
+#define DCD_THRESH_ON 30		// Hysteresis: Can miss 2 out of 32 for detecting lock.
+					// 31 is best for TNC Test CD.  30 almost as good.
+					// 30 better for 1200 regression test.
+#endif
+
+#ifndef DCD_THRESH_OFF
+#define DCD_THRESH_OFF 6		// Might want a little more fine tuning.
+#endif
+
+#ifndef DCD_GOOD_WIDTH
+#define DCD_GOOD_WIDTH 512		// No more than 1024!!!
+#endif
+
+__attribute__((always_inline))
+inline static void pll_dcd_signal_transition2 (struct demodulator_state_s *D, int slice, int dpll_phase)
+{
+	if (dpll_phase > - DCD_GOOD_WIDTH * 1024 * 1024 && dpll_phase < DCD_GOOD_WIDTH * 1024 * 1024) {
+	  D->slicer[slice].good_flag = 1;
+	}
+	else {
+	  D->slicer[slice].bad_flag = 1;
+	}
+}
+
+__attribute__((always_inline))
+inline static void pll_dcd_each_symbol2 (struct demodulator_state_s *D, int chan, int subchan, int slice)
+{
+	D->slicer[slice].good_hist <<= 1;
+	D->slicer[slice].good_hist |= D->slicer[slice].good_flag;
+	D->slicer[slice].good_flag = 0;
+
+	D->slicer[slice].bad_hist <<= 1;
+	D->slicer[slice].bad_hist |= D->slicer[slice].bad_flag;
+	D->slicer[slice].bad_flag = 0;
+
+	D->slicer[slice].score <<= 1;
+	// 2 is to detect 'flag' patterns with 2 transitions per octet.
+	D->slicer[slice].score |= (signed)__builtin_popcount(D->slicer[slice].good_hist)
+					- (signed)__builtin_popcount(D->slicer[slice].bad_hist) >= 2;
+
+	int s = __builtin_popcount(D->slicer[slice].score);
+	if (s >= DCD_THRESH_ON) {
+	  if (D->slicer[slice].data_detect == 0) {
+	    D->slicer[slice].data_detect = 1;
+	    dcd_change (chan, subchan, slice, D->slicer[slice].data_detect);
+	  }
+	}
+	else if (s <= DCD_THRESH_OFF) {
+	  if (D->slicer[slice].data_detect != 0) {
+	    D->slicer[slice].data_detect = 0;
+	    dcd_change (chan, subchan, slice, D->slicer[slice].data_detect);
+	  }
+	}
+}
+
+
 #define FSK_DEMOD_STATE_H 1
-#endif
+#endif