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 static float hysteresis_limit = 3000.0 / 32768.0;
  22 static bool do_calibrate = true;
  23 static bool output_cycles_plot = false;
  24
  25 // between [x,x+1]
  26 double find_zerocrossing(const std::vector<float> &pcm, int x)
  27 {
  28         if (pcm[x] == 0) {
  29                 return x;
  30         }
  31         if (pcm[x + 1] == 0) {
  32                 return x + 1;
  33         }
  34
  35         assert(pcm[x + 1] < 0);
  36         assert(pcm[x] > 0);
  37
  38         double upper = x;
  39         double lower = x + 1;
  40         while (lower - upper > 1e-3) {
  41                 double mid = 0.5f * (upper + lower);
  42                 if (lanczos_interpolate(pcm, mid) > 0) {
  43                         upper = mid;
  44                 } else {
  45                         lower = mid;
  46                 }
  47         }
  48
  49         return 0.5f * (upper + lower);
  50 }
  51
  52 struct pulse {
  53         double time;  // in seconds from start
  54         double len;   // in seconds
  55 };
  56
  57 // Calibrate on the first ~25k pulses (skip a few, just to be sure).
  58 double calibrate(const std::vector<pulse> &pulses) {
  59         if (pulses.size() < SYNC_PULSE_END) {
  60                 fprintf(stderr, "Too few pulses, not calibrating!\n");
  61                 return 1.0;
  62         }
  63
  64         int sync_pulse_end = -1;
  65         double sync_pulse_stddev = -1.0;
  66
  67         // Compute the standard deviation (to check for uneven speeds).
  68         // If it suddenly skyrockets, we assume that sync ended earlier
  69         // than we thought (it should be 25000 cycles), and that we should
  70         // calibrate on fewer cycles.
  71         for (int try_end : { 2000, 4000, 5000, 7500, 10000, 15000, SYNC_PULSE_END }) {
  72                 double sum2 = 0.0;
  73                 for (int i = SYNC_PULSE_START; i < try_end; ++i) {
  74                         double cycles = pulses[i].len * C64_FREQUENCY;
  75                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
  76                 }
  77                 double stddev = sqrt(sum2 / (try_end - SYNC_PULSE_START - 1));
  78                 if (sync_pulse_end != -1 && stddev > 5.0 && stddev / sync_pulse_stddev > 1.3) {
  79                         fprintf(stderr, "Stopping at %d sync pulses because standard deviation would be too big (%.2f cycles); shorter-than-usual trailer?\n",
  80                                 sync_pulse_end, stddev);
  81                         break;
  82                 }
  83                 sync_pulse_end = try_end;
  84                 sync_pulse_stddev = stddev;
  85         }
  86         fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
  87                 sync_pulse_stddev);
  88
  89         double sum = 0.0;
  90         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
  91                 sum += pulses[i].len;
  92         }
  93         double mean_length = C64_FREQUENCY * sum / (sync_pulse_end - SYNC_PULSE_START);
  94         double calibration_factor = SYNC_PULSE_LENGTH / mean_length;
  95         fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
  96                 mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
  97
  98         // Check for pulses outside +/- 10% (sign of misdetection).
  99         for (int i = SYNC_PULSE_START; i < sync_pulse_end; ++i) {
 100                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 101                 if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
 102                         fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 103                                 pulses[i].time, cycles);
 104                 }
 105         }
 106
 107         return calibration_factor;
 108 }
 109
 110 void output_tap(const std::vector<pulse>& pulses, double calibration_factor)
 111 {
 112         std::vector<char> tap_data;
 113         for (unsigned i = 0; i < pulses.size(); ++i) {
 114                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 115                 int len = lrintf(cycles / TAP_RESOLUTION);
 116                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 117                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 118                                         pulses[i].time, cycles);
 119                 }
 120                 if (len <= 255) {
 121                         tap_data.push_back(len);
 122                 } else {
 123                         int overflow_len = lrintf(cycles);
 124                         tap_data.push_back(0);
 125                         tap_data.push_back(overflow_len & 0xff);
 126                         tap_data.push_back((overflow_len >> 8) & 0xff);
 127                         tap_data.push_back(overflow_len >> 16);
 128                 }
 129         }
 130
 131         tap_header hdr;
 132         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
 133         hdr.version = 1;
 134         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
 135         hdr.data_len = tap_data.size();
 136
 137         fwrite(&hdr, sizeof(hdr), 1, stdout);
 138         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 139 }
 140
 141 static struct option long_options[] = {
 142         {"no-calibrate",     0,                 0, 's' },
 143         {"plot-cycles",      0,                 0, 'p' },
 144         {"hysteresis-limit", required_argument, 0, 'l' },
 145         {"help",             0,                 0, 'h' },
 146         {0,                  0,                 0, 0   }
 147 };
 148
 149 void help()
 150 {
 151         fprintf(stderr, "decode [OPTIONS] AUDIO-FILE > TAP-FILE\n");
 152         fprintf(stderr, "\n");
 153         fprintf(stderr, "  -s, --no-calibrate           do not try to calibrate on sync pulse length\n");
 154         fprintf(stderr, "  -p, --plot-cycles            output debugging info to cycles.plot\n");
 155         fprintf(stderr, "  -l, --hysteresis-limit VAL   change amplitude threshold for ignoring pulses (0..32768)\n");
 156         fprintf(stderr, "  -h, --help                   display this help, then exit\n");
 157         exit(1);
 158 }
 159
 160 void parse_options(int argc, char **argv)
 161 {
 162         for ( ;; ) {
 163                 int option_index = 0;
 164                 int c = getopt_long(argc, argv, "spl:h", long_options, &option_index);
 165                 if (c == -1)
 166                         break;
 167
 168                 switch (c) {
 169                 case 's':
 170                         do_calibrate = false;
 171                         break;
 172
 173                 case 'p':
 174                         output_cycles_plot = true;
 175                         break;
 176                 case 'l':
 177                         hysteresis_limit = atof(optarg) / 32768.0;
 178                         break;
 179
 180                 case 'h':
 181                 default:
 182                         help();
 183                         exit(1);
 184                 }
 185         }
 186 }
 187
 188 int main(int argc, char **argv)
 189 {
 190         parse_options(argc, argv);
 191
 192         make_lanczos_weight_table();
 193         std::vector<float> pcm;
 194         int sample_rate;
 195         if (!read_audio_file(argv[optind], &pcm, &sample_rate)) {
 196                 exit(1);
 197         }
 198
 199 #if 0
 200         for (int i = 0; i < LEN; ++i) {
 201                 in[i] += rand() % 10000;
 202         }
 203 #endif
 204
 205 #if 0
 206         for (int i = 0; i < LEN; ++i) {
 207                 printf("%d\n", in[i]);
 208         }
 209 #endif
 210
 211         std::vector<pulse> pulses;  // in seconds
 212
 213         // Find the flanks.
 214         int last_bit = -1;
 215         double last_downflank = -1;
 216         for (unsigned i = 0; i < pcm.size(); ++i) {
 217                 int bit = (pcm[i] > 0) ? 1 : 0;
 218                 if (bit == 0 && last_bit == 1) {
 219                         // Check if we ever go up above <hysteresis_limit> before we dip down again.
 220                         bool true_pulse = false;
 221                         unsigned j;
 222                         int min_level_after = 32767;
 223                         for (j = i; j < pcm.size(); ++j) {
 224                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
 225                                 if (pcm[j] > 0) break;
 226                                 if (pcm[j] < -hysteresis_limit) {
 227                                         true_pulse = true;
 228                                         break;
 229                                 }
 230                         }
 231
 232                         if (!true_pulse) {
 233 #if 0
 234                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
 235                                         double(i) / sample_rate, -min_level_after, hysteresis_limit);
 236 #endif
 237                                 i = j;
 238                                 continue;
 239                         }
 240
 241                         // down-flank!
 242                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate);
 243                         if (last_downflank > 0) {
 244                                 pulse p;
 245                                 p.time = t;
 246                                 p.len = t - last_downflank;
 247                                 pulses.push_back(p);
 248                         }
 249                         last_downflank = t;
 250                 }
 251                 last_bit = bit;
 252         }
 253
 254         double calibration_factor = 1.0;
 255         if (do_calibrate) {
 256                 calibration_factor = calibrate(pulses);
 257         }
 258
 259         if (output_cycles_plot) {
 260                 FILE *fp = fopen("cycles.plot", "w");
 261                 for (unsigned i = 0; i < pulses.size(); ++i) {
 262                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 263                         fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 264                 }
 265                 fclose(fp);
 266         }
 267
 268         output_tap(pulses, calibration_factor);
 269 }