From: Steinar H. Gunderson <sgunderson@bigfoot.com>
Date: Thu, 2 May 2013 21:29:04 +0000 (+0200)
Subject: Output TAP files, and do some more tests.
X-Git-Url: https://git.sesse.net/?p=c64tapwav;a=commitdiff_plain;h=65e6596055abd40573791be7ae031fa24b3dc169

Output TAP files, and do some more tests.
---

diff --git a/decode.c b/decode.c
index 923913d..85872a0 100644
--- a/decode.c
+++ b/decode.c
@@ -1,4 +1,5 @@
 #include <stdio.h>
+#include <string.h>
 #include <math.h>
 #include <unistd.h>
 #include <assert.h>
@@ -7,11 +8,21 @@
 
 #define LANCZOS_RADIUS 30
 #define BUFSIZE 4096
-#define HYSTERESIS_LIMIT 1000
+#define HYSTERESIS_LIMIT 3000
 #define SAMPLE_RATE 44100
 #define C64_FREQUENCY 985248
 #define TAP_RESOLUTION 8
 
+#define SYNC_PULSE_LENGTH 380.0
+#define SYNC_TEST_TOLERANCE 1.10
+
+struct tap_header {
+	char identifier[12];
+	char version;
+	char reserved[3];
+	unsigned int data_len;
+};
+
 double sinc(double x)
 {
 	if (fabs(x) < 1e-6) {
@@ -78,6 +89,11 @@ double find_zerocrossing(const std::vector<short> &pcm, int x)
 	return 0.5f * (upper + lower);
 }
 
+struct pulse {
+	double time;  // in seconds from start
+	double len;   // in seconds
+};
+	
 int main(int argc, char **argv)
 {
 	std::vector<short> pcm;
@@ -102,19 +118,22 @@ int main(int argc, char **argv)
 	}
 #endif
 
-	std::vector<float> pulse_lengths;  // in seconds
+	std::vector<pulse> pulses;  // in seconds
 
 	// Find the flanks.
 	int last_bit = -1;
 	double last_upflank = -1;
 	int last_max_level = 0;
-	for (int i = 0; i < pcm.size(); ++i) {
+	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) {
 			// up-flank!
 			double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
 			if (last_upflank > 0) {
-				pulse_lengths.push_back(t - last_upflank);
+				pulse p;
+				p.time = t;
+				p.len = t - last_upflank;
+				pulses.push_back(p);
 			}
 			last_upflank = t;
 			last_max_level = 0;
@@ -123,24 +142,55 @@ int main(int argc, char **argv)
 		last_bit = bit;
 	}
 
-	// Calibrate on the first ~15k pulses (skip a few, just to be sure).
-	float calibration_factor = 1.0f;
-	if (pulse_lengths.size() < 20000) {
+	// Calibrate on the first ~25k pulses (skip a few, just to be sure).
+	double calibration_factor = 1.0f;
+	if (pulses.size() < 20000) {
 		fprintf(stderr, "Too few pulses, not calibrating!\n");
 	} else {
 		double sum = 0.0;
-		for (int i = 1000; i < 16000; ++i) {
-			sum += pulse_lengths[i];
+		for (int i = 1000; i < 26000; ++i) {
+			sum += pulses[i].len;
 		}
-		double mean_length = C64_FREQUENCY * sum / 15000.0f;
-		calibration_factor = 380.0 / mean_length;
+		double mean_length = C64_FREQUENCY * sum / 25000.0f;
+		calibration_factor = SYNC_PULSE_LENGTH / mean_length;
 		fprintf(stderr, "Cycle length: %.2f -> 380.0 (change %+.2f%%)\n",
 			mean_length, 100.0 * (calibration_factor - 1.0));
+	
+		// Check for pulses outside +/- 10% (sign of misdetection).
+		for (int i = 1000; i < 25000; ++i) {
+			double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
+			if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
+				fprintf(stderr, "Sync cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
+					pulses[i].time, cycles);
+			}
+		}
 	}
 
-	for (int i = 0; i < pulse_lengths.size(); ++i) {
-		int len = lrintf(pulse_lengths[i] * calibration_factor * C64_FREQUENCY / TAP_RESOLUTION);
-		//fprintf(stderr, "length: %f (0x%x)\n", t - last_upflank, len);
-		printf("0x%x\n", len);
+	std::vector<char> tap_data;
+	for (unsigned i = 0; i < pulses.size(); ++i) {
+		double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
+		int len = lrintf(cycles / TAP_RESOLUTION);
+		if (i > 15000 && (cycles < 100 || cycles > 800)) {
+			fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
+					pulses[i].time, cycles);
+		}
+		if (len <= 255) {
+			tap_data.push_back(len);
+		} else {
+			int overflow_len = lrintf(cycles);
+			tap_data.push_back(0);
+			tap_data.push_back(overflow_len & 0xff);
+			tap_data.push_back((overflow_len >> 8) & 0xff);
+			tap_data.push_back(overflow_len >> 16);
+		}
 	}
+
+	tap_header hdr;
+	memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
+	hdr.version = 1;
+	hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
+	hdr.data_len = tap_data.size();
+
+	fwrite(&hdr, sizeof(hdr), 1, stdout);
+	fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 }