Improve the debouncing logic in the DTMF detector to fix some reliability

issues.  Previously, this code used a shift register of hits and non-hits.
However, if the start of the digit isn't clean, it is possible for the
leading edge detector to miss the digit.  These changes replace the flawed
shift register logic and also does the debouncing on the trailing edge as well.
(closes issue #10535, many thanks to softins for the patch)


git-svn-id: https://origsvn.digium.com/svn/asterisk/branches/1.4@80820 65c4cc65-6c06-0410-ace0-fbb531ad65f3

main/dsp.c

@@ -217,7 +217,7 @@ typedef struct
 	int hit3;
 	int hit4;
 #else
-	int hits[3];
+	int lasthit;
 #endif	
 	int mhit;
 	float energy;
@@ -371,7 +371,7 @@ static void ast_dtmf_detect_init (dtmf_detect_state_t *s)
 	s->hit4 = 
 	s->hit2 = 0;
 #else
-	s->hits[0] = s->hits[1] = s->hits[2] = 0;
+	s->lasthit = 0;
 #endif
 	for (i = 0;  i < 4;  i++) {
 		goertzel_init (&s->row_out[i], dtmf_row[i], 102);
@@ -595,6 +595,7 @@ static int dtmf_detect (dtmf_detect_state_t *s, int16_t amp[], int samples,
 						amp[i] = 0;
 					*writeback = 1;
 				}
+#ifdef OLD_DSP_ROUTINES
 				/* Look for two successive similar results */
 				/* The logic in the next test is:
 				   We need two successive identical clean detects, with
@@ -602,7 +603,6 @@ static int dtmf_detect (dtmf_detect_state_t *s, int16_t amp[], int samples,
 				   back to back differing digits. More importantly, it
 				   can work with nasty phones that give a very wobbly start
 				   to a digit */
-#ifdef OLD_DSP_ROUTINES
 				if (hit == s->hit3  &&  s->hit3 != s->hit2) {
 					s->mhit = hit;
 					s->digit_hits[(best_row << 2) + best_col]++;
@@ -614,21 +614,33 @@ static int dtmf_detect (dtmf_detect_state_t *s, int16_t amp[], int samples,
 						s->lost_digits++;
 					}
 				}
-#else				
-				if (hit == s->hits[2]  &&  hit != s->hits[1]  &&  hit != s->hits[0]) {
-					s->mhit = hit;
-					s->digit_hits[(best_row << 2) + best_col]++;
-					s->detected_digits++;
-					if (s->current_digits < MAX_DTMF_DIGITS) {
-						s->digits[s->current_digits++] = hit;
-						s->digits[s->current_digits] = '\0';
-					} else {
-						s->lost_digits++;
-					}
-				}
 #endif
 			}
 		} 
+
+#ifndef OLD_DSP_ROUTINES
+		/* Look for two successive similar results */
+		/* The logic in the next test is:
+		   We need two successive identical clean detects, with
+		   something different preceeding it. This can work with
+		   back to back differing digits. More importantly, it
+		   can work with nasty phones that give a very wobbly start
+		   to a digit */
+		if (hit == s->lasthit  &&  hit != s->mhit) {
+			if (hit) {
+				s->digit_hits[(best_row << 2) + best_col]++;
+				s->detected_digits++;
+				if (s->current_digits < MAX_DTMF_DIGITS) {
+					s->digits[s->current_digits++] = hit;
+					s->digits[s->current_digits] = '\0';
+				} else {
+					s->lost_digits++;
+				}
+			}
+			s->mhit = hit;
+		}
+#endif
+
 #ifdef FAX_DETECT
 		if (!hit && (fax_energy >= FAX_THRESHOLD) && 
 			(fax_energy >= DTMF_TO_TOTAL_ENERGY*s->energy) &&
@@ -659,9 +671,7 @@ static int dtmf_detect (dtmf_detect_state_t *s, int16_t amp[], int samples,
 		s->hit2 = s->hit3;
 		s->hit3 = hit;
 #else
-		s->hits[0] = s->hits[1];
-		s->hits[1] = s->hits[2];
-		s->hits[2] = hit;
+		s->lasthit = hit;
 #endif		
 		/* Reinitialise the detector for the next block */
 		for (i = 0;  i < 4;  i++) {
@@ -681,11 +691,15 @@ static int dtmf_detect (dtmf_detect_state_t *s, int16_t amp[], int samples,
 		s->energy = 0.0;
 		s->current_sample = 0;
 	}
+#ifdef OLD_DSP_ROUTINES
 	if ((!s->mhit) || (s->mhit != hit)) {
 		s->mhit = 0;
 		return(0);
 	}
 	return (hit);
+#else
+	return (s->mhit);	/* return the debounced hit */
+#endif
 }
 
 /* MF goertzel size */
@@ -1709,7 +1723,7 @@ void ast_dsp_digitreset(struct ast_dsp *dsp)
 #endif
 		dsp->td.dtmf.hit1 = dsp->td.dtmf.hit2 = dsp->td.dtmf.hit3 = dsp->td.dtmf.hit4 = dsp->td.dtmf.mhit = 0;
 #else
-		dsp->td.dtmf.hits[2] = dsp->td.dtmf.hits[1] = dsp->td.dtmf.hits[0] =  dsp->td.dtmf.mhit = 0;
+		dsp->td.dtmf.lasthit = dsp->td.dtmf.mhit = 0;
 #endif		
 		dsp->td.dtmf.energy = 0.0;
 		dsp->td.dtmf.current_sample = 0;