X-Git-Url: https://git.sesse.net/?p=c64tapwav;a=blobdiff_plain;f=decode.cpp;h=ca0c675e411fbddfca3037cddbbd7fc1e69083e7;hp=798a8729447ab143e51b3fd1bb9f1a11dad572be;hb=af205db54703906ad67adb6393a9df97c96357e8;hpb=35d290f19c02f0e884f4baec704851cfd1b86988;ds=sidebyside

diff --git a/decode.cpp b/decode.cpp
index 798a872..ca0c675 100644
--- a/decode.cpp
+++ b/decode.cpp
@@ -6,7 +6,8 @@
 #include <vector>
 #include <algorithm>
 
-#define LANCZOS_RADIUS 30
+#include "interpolate.h"
+
 #define BUFSIZE 4096
 #define HYSTERESIS_LIMIT 3000
 #define SAMPLE_RATE 44100
@@ -15,7 +16,7 @@
 
 #define SYNC_PULSE_START 1000
 #define SYNC_PULSE_END 15000
-#define SYNC_PULSE_LENGTH 380.0
+#define SYNC_PULSE_LENGTH 378.0
 #define SYNC_TEST_TOLERANCE 1.10
 
 struct tap_header {
@@ -25,45 +26,6 @@ struct tap_header {
 	unsigned int data_len;
 };
 
-double sinc(double x)
-{
-	if (fabs(x) < 1e-6) {
-		return 1.0f - fabs(x);
-	} else {
-		return sin(x) / x;
-	}
-}
-
-#if 0
-double weight(double x)
-{
-	if (fabs(x) > LANCZOS_RADIUS) {
-		return 0.0f;
-	}
-	return sinc(M_PI * x) * sinc(M_PI * x / LANCZOS_RADIUS);
-}
-#else
-double weight(double x)
-{
-	if (fabs(x) > 1.0f) {
-		return 0.0f;
-	}
-	return 1.0f - fabs(x);
-}
-#endif
-
-double interpolate(const std::vector<short> &pcm, double i)
-{
-	int lower = std::max<int>(ceil(i - LANCZOS_RADIUS), 0);
-	int upper = std::min<int>(floor(i + LANCZOS_RADIUS), pcm.size() - 1);
-	double sum = 0.0f;
-
-	for (int x = lower; x <= upper; ++x) {
-		sum += pcm[x] * weight(i - x);
-	}
-	return sum;
-}
-	
 // between [x,x+1]
 double find_zerocrossing(const std::vector<short> &pcm, int x)
 {
@@ -81,7 +43,7 @@ double find_zerocrossing(const std::vector<short> &pcm, int x)
 	double upper = x + 1;
 	while (upper - lower > 1e-6) {
 		double mid = 0.5f * (upper + lower);
-		if (interpolate(pcm, mid) > 0) {
+		if (lanczos_interpolate(pcm, mid) > 0) {
 			upper = mid;
 		} else {
 			lower = mid;
@@ -125,10 +87,31 @@ int main(int argc, char **argv)
 	// Find the flanks.
 	int last_bit = -1;
 	double last_upflank = -1;
-	int last_max_level = 0;
 	for (unsigned i = 0; i < pcm.size(); ++i) {
 		int bit = (pcm[i] > 0) ? 1 : 0;
-		if (bit == 1 && last_bit == 0 && last_max_level > HYSTERESIS_LIMIT) {
+		if (bit == 1 && last_bit == 0) {
+			// Check if we ever go up above HYSTERESIS_LIMIT before we dip down again.
+			bool true_pulse = false;
+			unsigned j;
+			int max_level_after = -32768;
+			for (j = i; j < pcm.size(); ++j) {
+				max_level_after = std::max<int>(max_level_after, pcm[j]);
+				if (pcm[j] < 0) break;
+				if (pcm[j] > HYSTERESIS_LIMIT) {
+					true_pulse = true;
+					break;
+				}
+			}
+
+			if (!true_pulse) {
+#if 0
+				fprintf(stderr, "Ignored up-flank at %.6f seconds due to hysteresis (%d < %d).\n",
+					double(i) / SAMPLE_RATE, max_level_after, HYSTERESIS_LIMIT);
+#endif
+				i = j;
+				continue;
+			} 
+
 			// up-flank!
 			double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
 			if (last_upflank > 0) {
@@ -138,9 +121,7 @@ int main(int argc, char **argv)
 				pulses.push_back(p);
 			}
 			last_upflank = t;
-			last_max_level = 0;
 		}
-		last_max_level = std::max(last_max_level, abs(pcm[i]));
 		last_bit = bit;
 	}
 
@@ -155,8 +136,8 @@ int main(int argc, char **argv)
 		}
 		double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
 		calibration_factor = SYNC_PULSE_LENGTH / mean_length;
-		fprintf(stderr, "Calibrated sync pulse length: %.2f -> 380.0 (change %+.2f%%)\n",
-			mean_length, 100.0 * (calibration_factor - 1.0));
+		fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
+			mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 
 		// Check for pulses outside +/- 10% (sign of misdetection).
 		for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
@@ -178,9 +159,11 @@ int main(int argc, char **argv)
 			stddev);
 	}
 
+	FILE *fp = fopen("cycles.plot", "w");
 	std::vector<char> tap_data;
 	for (unsigned i = 0; i < pulses.size(); ++i) {
 		double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
+		fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 		int len = lrintf(cycles / TAP_RESOLUTION);
 		if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 			fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
@@ -196,6 +179,7 @@ int main(int argc, char **argv)
 			tap_data.push_back(overflow_len >> 16);
 		}
 	}
+	fclose(fp);
 
 	tap_header hdr;
 	memcpy(hdr.identifier, "C64-TAPE-RAW", 12);