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 "audioreader.h"
  10 #include "interpolate.h"
  11 #include "tap.h"
  12
  13 #define BUFSIZE 4096
  14 #define HYSTERESIS_LIMIT 3000
  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         int sample_rate;
  59         if (!read_audio_file(argv[1], &pcm, &sample_rate)) {
  60                 exit(1);
  61         }
  62
  63 #if 0
  64         for (int i = 0; i < LEN; ++i) {
  65                 in[i] += rand() % 10000;
  66         }
  67 #endif
  68
  69 #if 0
  70         for (int i = 0; i < LEN; ++i) {
  71                 printf("%d\n", in[i]);
  72         }
  73 #endif
  74
  75         std::vector<pulse> pulses;  // in seconds
  76
  77         // Find the flanks.
  78         int last_bit = -1;
  79         double last_downflank = -1;
  80         for (unsigned i = 0; i < pcm.size(); ++i) {
  81                 int bit = (pcm[i] > 0) ? 1 : 0;
  82                 if (bit == 0 && last_bit == 1) {
  83                         // Check if we ever go up above HYSTERESIS_LIMIT before we dip down again.
  84                         bool true_pulse = false;
  85                         unsigned j;
  86                         int min_level_after = 32767;
  87                         for (j = i; j < pcm.size(); ++j) {
  88                                 min_level_after = std::min<int>(min_level_after, pcm[j]);
  89                                 if (pcm[j] > 0) break;
  90                                 if (pcm[j] < -HYSTERESIS_LIMIT) {
  91                                         true_pulse = true;
  92                                         break;
  93                                 }
  94                         }
  95
  96                         if (!true_pulse) {
  97 #if 0
  98                                 fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
  99                                         double(i) / sample_rate, -min_level_after, HYSTERESIS_LIMIT);
 100 #endif
 101                                 i = j;
 102                                 continue;
 103                         }
 104
 105                         // down-flank!
 106                         double t = find_zerocrossing(pcm, i - 1) * (1.0 / sample_rate);
 107                         if (last_downflank > 0) {
 108                                 pulse p;
 109                                 p.time = t;
 110                                 p.len = t - last_downflank;
 111                                 pulses.push_back(p);
 112                         }
 113                         last_downflank = t;
 114                 }
 115                 last_bit = bit;
 116         }
 117
 118         // Calibrate on the first ~25k pulses (skip a few, just to be sure).
 119         double calibration_factor = 1.0f;
 120         if (pulses.size() < SYNC_PULSE_END) {
 121                 fprintf(stderr, "Too few pulses, not calibrating!\n");
 122         } else {
 123                 double sum = 0.0;
 124                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
 125                         sum += pulses[i].len;
 126                 }
 127                 double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
 128                 calibration_factor = SYNC_PULSE_LENGTH / mean_length;
 129                 fprintf(stderr, "Calibrated sync pulse length: %.2f -> %.2f (change %+.2f%%)\n",
 130                         mean_length, SYNC_PULSE_LENGTH, 100.0 * (calibration_factor - 1.0));
 131
 132                 // Check for pulses outside +/- 10% (sign of misdetection).
 133                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
 134                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 135                         if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
 136                                 fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 137                                         pulses[i].time, cycles);
 138                         }
 139                 }
 140
 141                 // Compute the standard deviation (to check for uneven speeds).
 142                 double sum2 = 0.0;
 143                 for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
 144                         double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 145                         sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
 146                 }
 147                 double stddev = sqrt(sum2 / (SYNC_PULSE_END - SYNC_PULSE_START - 1));
 148                 fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
 149                         stddev);
 150         }
 151
 152         FILE *fp = fopen("cycles.plot", "w");
 153         std::vector<char> tap_data;
 154         for (unsigned i = 0; i < pulses.size(); ++i) {
 155                 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
 156                 fprintf(fp, "%f %f\n", pulses[i].time, cycles);
 157                 int len = lrintf(cycles / TAP_RESOLUTION);
 158                 if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
 159                         fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
 160                                         pulses[i].time, cycles);
 161                 }
 162                 if (len <= 255) {
 163                         tap_data.push_back(len);
 164                 } else {
 165                         int overflow_len = lrintf(cycles);
 166                         tap_data.push_back(0);
 167                         tap_data.push_back(overflow_len & 0xff);
 168                         tap_data.push_back((overflow_len >> 8) & 0xff);
 169                         tap_data.push_back(overflow_len >> 16);
 170                 }
 171         }
 172         fclose(fp);
 173
 174         tap_header hdr;
 175         memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
 176         hdr.version = 1;
 177         hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
 178         hdr.data_len = tap_data.size();
 179
 180         fwrite(&hdr, sizeof(hdr), 1, stdout);
 181         fwrite(tap_data.data(), tap_data.size(), 1, stdout);
 182
 183         // Output a debug raw file with pulse detection points.
 184         fp = fopen("debug.raw", "wb");
 185         short one = 32767;
 186         short zero = 0;
 187         unsigned pulsenum = 0;
 188         for (unsigned i = 0; i < pcm.size(); ++i) {
 189                 unsigned next_pulse = (pulsenum >= pulses.size()) ? INT_MAX : int(pulses[pulsenum].time * sample_rate);
 190                 if (i >= next_pulse) {
 191                         fwrite(&one, sizeof(one), 1, fp);
 192                         ++pulsenum;
 193                 } else {
 194                         fwrite(&zero, sizeof(zero), 1, fp);
 195                 }
 196         }
 197         fclose(fp);
 198 }