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 static bool quiet = false;
  30
  31 // between [x,x+1]
  32 double find_zerocrossing(const std::vector<float> &pcm, int x)
  33 {
  34         if (pcm[x] == 0) {
  35                 return x;
  36         }
  37         if (pcm[x + 1] == 0) {
  38                 return x + 1;
  39         }
  40
  41         assert(pcm[x + 1] < 0);
  42         assert(pcm[x] > 0);
  43
  44         double upper = x;
  45         double lower = x + 1;
  46         while (lower - upper > 1e-3) {
  47                 double mid = 0.5f * (upper + lower);
  48                 if (lanczos_interpolate(pcm, mid) > 0) {
  49                         upper = mid;
  50                 } else {
  51                         lower = mid;
  52                 }
  53         }
  54
  55         return 0.5f * (upper + lower);
  56 }
  57
  58 struct pulse {
  59         double time;  // in seconds from start
  60         double len;   // in seconds
  61 };
  62
  63 // Calibrate on the first ~25k pulses (skip a few, just to be sure).
  64 double calibrate(const std::vector<pulse> &pulses) {
  65         if (pulses.size() < SYNC_PULSE_END) {
  66                 fprintf(stderr, "Too few pulses, not calibrating!\n");
  67                 return 1.0;
  68         }
  69
  70         int sync_pulse_end = -1;
  71         double sync_pulse_stddev = -1.0;
  72
  73         // Compute the standard deviation (to check for uneven speeds).
  74         // If it suddenly skyrockets, we assume that sync ended earlier
  75         // than we thought (it should be 25000 cycles), and that we should
  76         // calibrate on fewer cycles.
  77         for (int try_end : { 2000, 4000, 5000, 7500, 10000, 15000, SYNC_PULSE_END }) {
  78                 double sum2 = 0.0;
  79                 for (int i = SYNC_PULSE_START; i < try_end; ++i) {
  80                         double cycles = pulses[i].len * C64_FREQUENCY;
  81                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
  82                 }
  83                 double stddev = sqrt(sum2 / (try_end - SYNC_PULSE_START - 1));
  84                 if (sync_pulse_end != -1 && stddev > 5.0 && stddev / sync_pulse_stddev > 1.3) {
  85                         fprintf(stderr, "Stopping at %d sync pulses because standard deviation would be too big (%.2f cycles); shorter-than-usual trailer?\n",
  86                                 sync_pulse_end, stddev);
  87                         break;
  88                 }
  89                 sync_pulse_end = try_end;
  90                 sync_pulse_stddev = stddev;
  91         }
  92         if (!quiet) {
  93                 fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
  94                         sync_pulse_stddev);
  95         }
  96
  97         double sum = 0.0;
  98         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
  99                 sum += pulses[i].len;
 100         }
 101         double mean_length = C64_FREQUENCY * sum / (sync_pulse_end - SYNC_PULSE_START);
 102         double calibration_factor = SYNC_PULSE_LENGTH / mean_length;
 103         if (!quiet) {
 104                 fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
 105                         mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 106         }
 107
 108         // Check for pulses outside +/- 10% (sign of misdetection).
 109         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
 110                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 111                 if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
 112                         fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 113                                 pulses[i].time, cycles);
 114                 }
 115         }
 116
 117         return calibration_factor;
 118 }
 119
 120 void output_tap(const std::vector<pulse>& pulses, double calibration_factor)
 121 {
 122         std::vector<char> tap_data;
 123         for (unsigned i = 0; i < pulses.size(); ++i) {
 124                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 125                 int len = lrintf(cycles / TAP_RESOLUTION);
 126                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 127                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 128                                         pulses[i].time, cycles);
 129                 }
 130                 if (len <= 255) {
 131                         tap_data.push_back(len);
 132                 } else {
 133                         int overflow_len = lrintf(cycles);
 134                         tap_data.push_back(0);
 135                         tap_data.push_back(overflow_len & 0xff);
 136                         tap_data.push_back((overflow_len >> 8) & 0xff);
 137                         tap_data.push_back(overflow_len >> 16);
 138                 }
 139         }
 140
 141         tap_header hdr;
 142         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
 143         hdr.version = 1;
 144         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
 145         hdr.data_len = tap_data.size();
 146
 147         fwrite(&hdr, sizeof(hdr), 1, stdout);
 148         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 149 }
 150
 151 static struct option long_options[] = {
 152         {"no-calibrate",     0,                 0, 's' },
 153         {"plot-cycles",      0,                 0, 'p' },
 154         {"hysteresis-limit", required_argument, 0, 'l' },
 155         {"filter",           required_argument, 0, 'f' },
 156         {"output-filtered",  0,                 0, 'F' },
 157         {"quiet",            0,                 0, 'q' },
 158         {"help",             0,                 0, 'h' },
 159         {0,                  0,                 0, 0   }
 160 };
 161
 162 void help()
 163 {
 164         fprintf(stderr, "decode [OPTIONS] AUDIO-FILE > TAP-FILE\n");
 165         fprintf(stderr, "\n");
 166         fprintf(stderr, "  -s, --no-calibrate           do not try to calibrate on sync pulse length\n");
 167         fprintf(stderr, "  -p, --plot-cycles            output debugging info to cycles.plot\n");
 168         fprintf(stderr, "  -l, --hysteresis-limit VAL   change amplitude threshold for ignoring pulses (0..32768)\n");
 169         fprintf(stderr, "  -f, --filter C1:C2:C3:...    specify FIR filter (up to %d coefficients)\n", NUM_FILTER_COEFF);
 170         fprintf(stderr, "  -F, --output-filtered        output filtered waveform to filtered.raw\n");
 171         fprintf(stderr, "  -q, --quiet                  suppress some informational messages\n");
 172         fprintf(stderr, "  -h, --help                   display this help, then exit\n");
 173         exit(1);
 174 }
 175
 176 void parse_options(int argc, char **argv)
 177 {
 178         for ( ;; ) {
 179                 int option_index = 0;
 180                 int c = getopt_long(argc, argv, "spl:f:Fqh", long_options, &option_index);
 181                 if (c == -1)
 182                         break;
 183
 184                 switch (c) {
 185                 case 's':
 186                         do_calibrate = false;
 187                         break;
 188
 189                 case 'p':
 190                         output_cycles_plot = true;
 191                         break;
 192
 193                 case 'l':
 194                         hysteresis_limit = atof(optarg) / 32768.0;
 195                         break;
 196
 197                 case 'f': {
 198                         const char *coeffstr = strtok(optarg, ":");
 199                         int coeff_index = 0;
 200                         while (coeff_index < NUM_FILTER_COEFF && coeffstr != NULL) {
 201                                 filter_coeff[coeff_index++] = atof(coeffstr);
 202                                 coeffstr = strtok(NULL, ":");
 203                         }
 204                         use_filter = true;
 205                         break;
 206                 }
 207
 208                 case 'F':
 209                         output_filtered = true;
 210                         break;
 211
 212                 case 'q':
 213                         quiet = true;
 214                         break;
 215
 216                 case 'h':
 217                 default:
 218                         help();
 219                         exit(1);
 220                 }
 221         }
 222 }
 223
 224 // TODO: Support AVX here.
 225 std::vector<float> do_filter(const std::vector<float>& pcm, const float* filter)
 226 {
 227         std::vector<float> filtered_pcm;
 228         filtered_pcm.reserve(pcm.size());
 229         for (unsigned i = NUM_FILTER_COEFF; i < pcm.size(); ++i) {
 230                 float s = 0.0f;
 231                 for (int j = 0; j < NUM_FILTER_COEFF; ++j) {
 232                         s += filter[j] * pcm[i - j];
 233                 }
 234                 filtered_pcm.push_back(s);
 235         }
 236
 237         if (output_filtered) {
 238                 FILE *fp = fopen("filtered.raw", "wb");
 239                 fwrite(filtered_pcm.data(), filtered_pcm.size() * sizeof(filtered_pcm[0]), 1, fp);
 240                 fclose(fp);
 241         }
 242
 243         return filtered_pcm;
 244 }
 245
 246 std::vector<pulse> detect_pulses(const std::vector<float> &pcm, int sample_rate)
 247 {
 248         std::vector<pulse> pulses;
 249
 250         // Find the flanks.
 251         int last_bit = -1;
 252         double last_downflank = -1;
 253         for (unsigned i = 0; i < pcm.size(); ++i) {
 254                 int bit = (pcm[i] > 0) ? 1 : 0;
 255                 if (bit == 0 && last_bit == 1) {
 256                         // Check if we ever go up above <hysteresis_limit> before we dip down again.
 257                         bool true_pulse = false;
 258                         unsigned j;
 259                         int min_level_after = 32767;
 260                         for (j = i; j < pcm.size(); ++j) {
 261                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
 262                                 if (pcm[j] > 0) break;
 263                                 if (pcm[j] < -hysteresis_limit) {
 264                                         true_pulse = true;
 265                                         break;
 266                                 }
 267                         }
 268
 269                         if (!true_pulse) {
 270 #if 0
 271                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
 272                                         double(i) / sample_rate, -min_level_after, hysteresis_limit);
 273 #endif
 274                                 i = j;
 275                                 continue;
 276                         }
 277
 278                         // down-flank!
 279                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate);
 280                         if (last_downflank > 0) {
 281                                 pulse p;
 282                                 p.time = t;
 283                                 p.len = t - last_downflank;
 284                                 pulses.push_back(p);
 285                         }
 286                         last_downflank = t;
 287                 }
 288                 last_bit = bit;
 289         }
 290         return pulses;
 291 }
 292
 293 int main(int argc, char **argv)
 294 {
 295         parse_options(argc, argv);
 296
 297         make_lanczos_weight_table();
 298         std::vector<float> pcm;
 299         int sample_rate;
 300         if (!read_audio_file(argv[optind], &pcm, &sample_rate)) {
 301                 exit(1);
 302         }
 303
 304         if (use_filter) {
 305                 pcm = do_filter(pcm, filter_coeff);
 306         }
 307
 308 #if 0
 309         for (int i = 0; i < LEN; ++i) {
 310                 in[i] += rand() % 10000;
 311         }
 312 #endif
 313
 314 #if 0
 315         for (int i = 0; i < LEN; ++i) {
 316                 printf("%d\n", in[i]);
 317         }
 318 #endif
 319
 320         std::vector<pulse> pulses = detect_pulses(pcm, sample_rate);
 321
 322         double calibration_factor = 1.0;
 323         if (do_calibrate) {
 324                 calibration_factor = calibrate(pulses);
 325         }
 326
 327         if (output_cycles_plot) {
 328                 FILE *fp = fopen("cycles.plot", "w");
 329                 for (unsigned i = 0; i < pulses.size(); ++i) {
 330                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 331                         fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 332                 }
 333                 fclose(fp);
 334         }
 335
 336         output_tap(pulses, calibration_factor);
 337 }