git.sesse.net Git - c64tapwav/blob - decode.cpp

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