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 <getopt.h>
   7 #include <vector>
   8 #include <algorithm>
   9
  10 #include "audioreader.h"
  11 #include "interpolate.h"
  12 #include "tap.h"
  13
  14 #define BUFSIZE 4096
  15 #define C64_FREQUENCY 985248
  16 #define SYNC_PULSE_START 1000
  17 #define SYNC_PULSE_END 20000
  18 #define SYNC_PULSE_LENGTH 378.0
  19 #define SYNC_TEST_TOLERANCE 1.10
  20
  21 #define NUM_FILTER_COEFF 32
  22
  23 static float hysteresis_limit = 3000.0 / 32768.0;
  24 static bool do_calibrate = true;
  25 static bool output_cycles_plot = false;
  26 static bool use_filter = false;
  27 static float filter_coeff[NUM_FILTER_COEFF] = { 1.0f };  // The rest is filled with 0.
  28 static bool output_filtered = false;
  29
  30 // between [x,x+1]
  31 double find_zerocrossing(const std::vector<float> &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 (lower - upper > 1e-3) {
  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 // Calibrate on the first ~25k pulses (skip a few, just to be sure).
  63 double calibrate(const std::vector<pulse> &pulses) {
  64         if (pulses.size() < SYNC_PULSE_END) {
  65                 fprintf(stderr, "Too few pulses, not calibrating!\n");
  66                 return 1.0;
  67         }
  68
  69         int sync_pulse_end = -1;
  70         double sync_pulse_stddev = -1.0;
  71
  72         // Compute the standard deviation (to check for uneven speeds).
  73         // If it suddenly skyrockets, we assume that sync ended earlier
  74         // than we thought (it should be 25000 cycles), and that we should
  75         // calibrate on fewer cycles.
  76         for (int try_end : { 2000, 4000, 5000, 7500, 10000, 15000, SYNC_PULSE_END }) {
  77                 double sum2 = 0.0;
  78                 for (int i = SYNC_PULSE_START; i < try_end; ++i) {
  79                         double cycles = pulses[i].len * C64_FREQUENCY;
  80                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
  81                 }
  82                 double stddev = sqrt(sum2 / (try_end - SYNC_PULSE_START - 1));
  83                 if (sync_pulse_end != -1 && stddev > 5.0 && stddev / sync_pulse_stddev > 1.3) {
  84                         fprintf(stderr, "Stopping at %d sync pulses because standard deviation would be too big (%.2f cycles); shorter-than-usual trailer?\n",
  85                                 sync_pulse_end, stddev);
  86                         break;
  87                 }
  88                 sync_pulse_end = try_end;
  89                 sync_pulse_stddev = stddev;
  90         }
  91         fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
  92                 sync_pulse_stddev);
  93
  94         double sum = 0.0;
  95         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
  96                 sum += pulses[i].len;
  97         }
  98         double mean_length = C64_FREQUENCY * sum / (sync_pulse_end - SYNC_PULSE_START);
  99         double calibration_factor = SYNC_PULSE_LENGTH / mean_length;
 100         fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
 101                 mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 102
 103         // Check for pulses outside +/- 10% (sign of misdetection).
 104         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
 105                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 106                 if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
 107                         fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 108                                 pulses[i].time, cycles);
 109                 }
 110         }
 111
 112         return calibration_factor;
 113 }
 114
 115 void output_tap(const std::vector<pulse>& pulses, double calibration_factor)
 116 {
 117         std::vector<char> tap_data;
 118         for (unsigned i = 0; i < pulses.size(); ++i) {
 119                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 120                 int len = lrintf(cycles / TAP_RESOLUTION);
 121                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 122                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 123                                         pulses[i].time, cycles);
 124                 }
 125                 if (len <= 255) {
 126                         tap_data.push_back(len);
 127                 } else {
 128                         int overflow_len = lrintf(cycles);
 129                         tap_data.push_back(0);
 130                         tap_data.push_back(overflow_len & 0xff);
 131                         tap_data.push_back((overflow_len >> 8) & 0xff);
 132                         tap_data.push_back(overflow_len >> 16);
 133                 }
 134         }
 135
 136         tap_header hdr;
 137         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
 138         hdr.version = 1;
 139         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
 140         hdr.data_len = tap_data.size();
 141
 142         fwrite(&hdr, sizeof(hdr), 1, stdout);
 143         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 144 }
 145
 146 static struct option long_options[] = {
 147         {"no-calibrate",     0,                 0, 's' },
 148         {"plot-cycles",      0,                 0, 'p' },
 149         {"hysteresis-limit", required_argument, 0, 'l' },
 150         {"filter",           required_argument, 0, 'f' },
 151         {"output-filtered",  0,                 0, 'F' },
 152         {"help",             0,                 0, 'h' },
 153         {0,                  0,                 0, 0   }
 154 };
 155
 156 void help()
 157 {
 158         fprintf(stderr, "decode [OPTIONS] AUDIO-FILE > TAP-FILE\n");
 159         fprintf(stderr, "\n");
 160         fprintf(stderr, "  -s, --no-calibrate           do not try to calibrate on sync pulse length\n");
 161         fprintf(stderr, "  -p, --plot-cycles            output debugging info to cycles.plot\n");
 162         fprintf(stderr, "  -l, --hysteresis-limit VAL   change amplitude threshold for ignoring pulses (0..32768)\n");
 163         fprintf(stderr, "  -f, --filter C1:C2:C3:...    specify FIR filter (up to %d coefficients)\n", NUM_FILTER_COEFF);
 164         fprintf(stderr, "  -F, --output-filtered        output filtered waveform to filtered.raw\n");
 165         fprintf(stderr, "  -h, --help                   display this help, then exit\n");
 166         exit(1);
 167 }
 168
 169 void parse_options(int argc, char **argv)
 170 {
 171         for ( ;; ) {
 172                 int option_index = 0;
 173                 int c = getopt_long(argc, argv, "spl:f:Fh", long_options, &option_index);
 174                 if (c == -1)
 175                         break;
 176
 177                 switch (c) {
 178                 case 's':
 179                         do_calibrate = false;
 180                         break;
 181
 182                 case 'p':
 183                         output_cycles_plot = true;
 184                         break;
 185                 case 'l':
 186                         hysteresis_limit = atof(optarg) / 32768.0;
 187                         break;
 188
 189                 case 'f': {
 190                         const char *coeffstr = strtok(optarg, ":");
 191                         int coeff_index = 0;
 192                         while (coeff_index < NUM_FILTER_COEFF && coeffstr != NULL) {
 193                                 filter_coeff[coeff_index++] = atof(coeffstr);
 194                                 coeffstr = strtok(NULL, ":");
 195                         }
 196                         use_filter = true;
 197                         break;
 198                 }
 199
 200                 case 'F':
 201                         output_filtered = true;
 202                         break;
 203
 204                 case 'h':
 205                 default:
 206                         help();
 207                         exit(1);
 208                 }
 209         }
 210 }
 211
 212 // TODO: Support AVX here.
 213 std::vector<float> do_filter(const std::vector<float>& pcm, const float* filter)
 214 {
 215         std::vector<float> filtered_pcm;
 216         filtered_pcm.reserve(pcm.size());
 217         for (unsigned i = NUM_FILTER_COEFF; i < pcm.size(); ++i) {
 218                 float s = 0.0f;
 219                 for (int j = 0; j < NUM_FILTER_COEFF; ++j) {
 220                         s += filter[j] * pcm[i - j];
 221                 }
 222                 filtered_pcm.push_back(s);
 223         }
 224
 225         if (output_filtered) {
 226                 FILE *fp = fopen("filtered.raw", "wb");
 227                 fwrite(filtered_pcm.data(), filtered_pcm.size() * sizeof(filtered_pcm[0]), 1, fp);
 228                 fclose(fp);
 229         }
 230
 231         return filtered_pcm;
 232 }
 233
 234 int main(int argc, char **argv)
 235 {
 236         parse_options(argc, argv);
 237
 238         make_lanczos_weight_table();
 239         std::vector<float> pcm;
 240         int sample_rate;
 241         if (!read_audio_file(argv[optind], &pcm, &sample_rate)) {
 242                 exit(1);
 243         }
 244
 245         if (use_filter) {
 246                 pcm = do_filter(pcm, filter_coeff);
 247         }
 248
 249 #if 0
 250         for (int i = 0; i < LEN; ++i) {
 251                 in[i] += rand() % 10000;
 252         }
 253 #endif
 254
 255 #if 0
 256         for (int i = 0; i < LEN; ++i) {
 257                 printf("%d\n", in[i]);
 258         }
 259 #endif
 260
 261         std::vector<pulse> pulses;  // in seconds
 262
 263         // Find the flanks.
 264         int last_bit = -1;
 265         double last_downflank = -1;
 266         for (unsigned i = 0; i < pcm.size(); ++i) {
 267                 int bit = (pcm[i] > 0) ? 1 : 0;
 268                 if (bit == 0 && last_bit == 1) {
 269                         // Check if we ever go up above <hysteresis_limit> before we dip down again.
 270                         bool true_pulse = false;
 271                         unsigned j;
 272                         int min_level_after = 32767;
 273                         for (j = i; j < pcm.size(); ++j) {
 274                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
 275                                 if (pcm[j] > 0) break;
 276                                 if (pcm[j] < -hysteresis_limit) {
 277                                         true_pulse = true;
 278                                         break;
 279                                 }
 280                         }
 281
 282                         if (!true_pulse) {
 283 #if 0
 284                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
 285                                         double(i) / sample_rate, -min_level_after, hysteresis_limit);
 286 #endif
 287                                 i = j;
 288                                 continue;
 289                         }
 290
 291                         // down-flank!
 292                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate);
 293                         if (last_downflank > 0) {
 294                                 pulse p;
 295                                 p.time = t;
 296                                 p.len = t - last_downflank;
 297                                 pulses.push_back(p);
 298                         }
 299                         last_downflank = t;
 300                 }
 301                 last_bit = bit;
 302         }
 303
 304         double calibration_factor = 1.0;
 305         if (do_calibrate) {
 306                 calibration_factor = calibrate(pulses);
 307         }
 308
 309         if (output_cycles_plot) {
 310                 FILE *fp = fopen("cycles.plot", "w");
 311                 for (unsigned i = 0; i < pulses.size(); ++i) {
 312                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 313                         fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 314                 }
 315                 fclose(fp);
 316         }
 317
 318         output_tap(pulses, calibration_factor);
 319 }