fdc1347e0e124a7297ab4c6ef4a71e644c58f0fd
[c64tapwav] / decode.cpp
1 #include <stdio.h>
2 #include <string.h>
3 #include <math.h>
4 #include <unistd.h>
5 #include <assert.h>
6 #include <limits.h>
7 #include <vector>
8 #include <algorithm>
9
10 #include "interpolate.h"
11
12 #define BUFSIZE 4096
13 #define HYSTERESIS_LIMIT 3000
14 #define SAMPLE_RATE 44100
15 #define C64_FREQUENCY 985248
16 #define TAP_RESOLUTION 8
17
18 #define SYNC_PULSE_START 1000
19 #define SYNC_PULSE_END 15000
20 #define SYNC_PULSE_LENGTH 378.0
21 #define SYNC_TEST_TOLERANCE 1.10
22
23 struct tap_header {
24         char identifier[12];
25         char version;
26         char reserved[3];
27         unsigned int data_len;
28 };
29
30 // between [x,x+1]
31 double find_zerocrossing(const std::vector<short> &pcm, int x)
32 {
33         if (pcm[x] == 0) {
34                 return x;
35         }
36         if (pcm[x + 1] == 0) {
37                 return x + 1;
38         }
39
40         assert(pcm[x + 1] < 0);
41         assert(pcm[x] > 0);
42
43         double upper = x;
44         double lower = x + 1;
45         while (upper - lower > 1e-6) {
46                 double mid = 0.5f * (upper + lower);
47                 if (lanczos_interpolate(pcm, mid) > 0) {
48                         upper = mid;
49                 } else {
50                         lower = mid;
51                 }
52         }
53
54         return 0.5f * (upper + lower);
55 }
56
57 struct pulse {
58         double time;  // in seconds from start
59         double len;   // in seconds
60 };
61         
62 int main(int argc, char **argv)
63 {
64         std::vector<short> pcm;
65
66         while (!feof(stdin)) {
67                 short buf[BUFSIZE];
68                 ssize_t ret = fread(buf, 2, BUFSIZE, stdin);
69                 if (ret >= 0) {
70                         pcm.insert(pcm.end(), buf, buf + ret);
71                 }
72         }       
73
74 #if 0
75         for (int i = 0; i < LEN; ++i) {
76                 in[i] += rand() % 10000;
77         }
78 #endif
79
80 #if 0
81         for (int i = 0; i < LEN; ++i) {
82                 printf("%d\n", in[i]);
83         }
84 #endif
85
86         std::vector<pulse> pulses;  // in seconds
87
88         // Find the flanks.
89         int last_bit = -1;
90         double last_downflank = -1;
91         for (unsigned i = 0; i < pcm.size(); ++i) {
92                 int bit = (pcm[i] > 0) ? 1 : 0;
93                 if (bit == 0 && last_bit == 1) {
94                         // Check if we ever go up above HYSTERESIS_LIMIT before we dip down again.
95                         bool true_pulse = false;
96                         unsigned j;
97                         int min_level_after = 32767;
98                         for (j = i; j < pcm.size(); ++j) {
99                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
100                                 if (pcm[j] > 0) break;
101                                 if (pcm[j] < -HYSTERESIS_LIMIT) {
102                                         true_pulse = true;
103                                         break;
104                                 }
105                         }
106
107                         if (!true_pulse) {
108 #if 0
109                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
110                                         double(i) / SAMPLE_RATE, -min_level_after, HYSTERESIS_LIMIT);
111 #endif
112                                 i = j;
113                                 continue;
114                         } 
115
116                         // down-flank!
117                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
118                         if (last_downflank > 0) {
119                                 pulse p;
120                                 p.time = t;
121                                 p.len = t - last_downflank;
122                                 pulses.push_back(p);
123                         }
124                         last_downflank = t;
125                 }
126                 last_bit = bit;
127         }
128
129         // Calibrate on the first ~25k pulses (skip a few, just to be sure).
130         double calibration_factor = 1.0f;
131         if (pulses.size() < SYNC_PULSE_END) {
132                 fprintf(stderr, "Too few pulses, not calibrating!\n");
133         } else {
134                 double sum = 0.0;
135                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
136                         sum += pulses[i].len;
137                 }
138                 double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
139                 calibration_factor = SYNC_PULSE_LENGTH / mean_length;
140                 fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
141                         mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
142
143                 // Check for pulses outside +/- 10% (sign of misdetection).
144                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
145                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
146                         if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
147                                 fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
148                                         pulses[i].time, cycles);
149                         }
150                 }
151
152                 // Compute the standard deviation (to check for uneven speeds).
153                 double sum2 = 0.0;
154                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
155                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
156                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
157                 }
158                 double stddev = sqrt(sum2 / (SYNC_PULSE_END - SYNC_PULSE_START - 1));
159                 fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
160                         stddev);
161         }
162
163         FILE *fp = fopen("cycles.plot", "w");
164         std::vector<char> tap_data;
165         for (unsigned i = 0; i < pulses.size(); ++i) {
166                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
167                 fprintf(fp, "%f %f\n", pulses[i].time, cycles);
168                 int len = lrintf(cycles / TAP_RESOLUTION);
169                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
170                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
171                                         pulses[i].time, cycles);
172                 }
173                 if (len <= 255) {
174                         tap_data.push_back(len);
175                 } else {
176                         int overflow_len = lrintf(cycles);
177                         tap_data.push_back(0);
178                         tap_data.push_back(overflow_len & 0xff);
179                         tap_data.push_back((overflow_len >> 8) & 0xff);
180                         tap_data.push_back(overflow_len >> 16);
181                 }
182         }
183         fclose(fp);
184
185         tap_header hdr;
186         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
187         hdr.version = 1;
188         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
189         hdr.data_len = tap_data.size();
190
191         fwrite(&hdr, sizeof(hdr), 1, stdout);
192         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
193
194         // Output a debug raw file with pulse detection points.
195         fp = fopen("debug.raw", "wb");
196         short one = 32767;
197         short zero = 0;
198         unsigned pulsenum = 0;
199         for (unsigned i = 0; i < pcm.size(); ++i) {
200                 unsigned next_pulse = (pulsenum >= pulses.size()) ? INT_MAX : int(pulses[pulsenum].time * SAMPLE_RATE);
201                 if (i >= next_pulse) {
202                         fwrite(&one, sizeof(one), 1, fp);
203                         ++pulsenum;
204                 } else {
205                         fwrite(&zero, sizeof(zero), 1, fp);
206                 }
207         }
208         fclose(fp);
209 }