9 #define LANCZOS_RADIUS 30
11 #define HYSTERESIS_LIMIT 3000
12 #define SAMPLE_RATE 44100
13 #define C64_FREQUENCY 985248
14 #define TAP_RESOLUTION 8
16 #define SYNC_PULSE_LENGTH 380.0
17 #define SYNC_TEST_TOLERANCE 1.10
23 unsigned int data_len;
29 return 1.0f - fabs(x);
36 double weight(double x)
38 if (fabs(x) > LANCZOS_RADIUS) {
41 return sinc(M_PI * x) * sinc(M_PI * x / LANCZOS_RADIUS);
44 double weight(double x)
49 return 1.0f - fabs(x);
53 double interpolate(const std::vector<short> &pcm, double i)
55 int lower = std::max<int>(ceil(i - LANCZOS_RADIUS), 0);
56 int upper = std::min<int>(floor(i + LANCZOS_RADIUS), pcm.size() - 1);
59 for (int x = lower; x <= upper; ++x) {
60 sum += pcm[x] * weight(i - x);
66 double find_zerocrossing(const std::vector<short> &pcm, int x)
71 if (pcm[x + 1] == 0) {
75 assert(pcm[x + 1] > 0);
80 while (upper - lower > 1e-6) {
81 double mid = 0.5f * (upper + lower);
82 if (interpolate(pcm, mid) > 0) {
89 return 0.5f * (upper + lower);
93 double time; // in seconds from start
94 double len; // in seconds
97 int main(int argc, char **argv)
99 std::vector<short> pcm;
101 while (!feof(stdin)) {
103 ssize_t ret = fread(buf, 2, BUFSIZE, stdin);
105 pcm.insert(pcm.end(), buf, buf + ret);
110 for (int i = 0; i < LEN; ++i) {
111 in[i] += rand() % 10000;
116 for (int i = 0; i < LEN; ++i) {
117 printf("%d\n", in[i]);
121 std::vector<pulse> pulses; // in seconds
125 double last_upflank = -1;
126 int last_max_level = 0;
127 for (unsigned i = 0; i < pcm.size(); ++i) {
128 int bit = (pcm[i] > 0) ? 1 : 0;
129 if (bit == 1 && last_bit == 0 && last_max_level > HYSTERESIS_LIMIT) {
131 double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
132 if (last_upflank > 0) {
135 p.len = t - last_upflank;
141 last_max_level = std::max(last_max_level, abs(pcm[i]));
145 // Calibrate on the first ~25k pulses (skip a few, just to be sure).
146 double calibration_factor = 1.0f;
147 if (pulses.size() < 20000) {
148 fprintf(stderr, "Too few pulses, not calibrating!\n");
151 for (int i = 1000; i < 26000; ++i) {
152 sum += pulses[i].len;
154 double mean_length = C64_FREQUENCY * sum / 25000.0f;
155 calibration_factor = SYNC_PULSE_LENGTH / mean_length;
156 fprintf(stderr, "Cycle length: %.2f -> 380.0 (change %+.2f%%)\n",
157 mean_length, 100.0 * (calibration_factor - 1.0));
159 // Check for pulses outside +/- 10% (sign of misdetection).
160 for (int i = 1000; i < 25000; ++i) {
161 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
162 if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
163 fprintf(stderr, "Sync cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
164 pulses[i].time, cycles);
169 std::vector<char> tap_data;
170 for (unsigned i = 0; i < pulses.size(); ++i) {
171 double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
172 int len = lrintf(cycles / TAP_RESOLUTION);
173 if (i > 15000 && (cycles < 100 || cycles > 800)) {
174 fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
175 pulses[i].time, cycles);
178 tap_data.push_back(len);
180 int overflow_len = lrintf(cycles);
181 tap_data.push_back(0);
182 tap_data.push_back(overflow_len & 0xff);
183 tap_data.push_back((overflow_len >> 8) & 0xff);
184 tap_data.push_back(overflow_len >> 16);
189 memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
191 hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
192 hdr.data_len = tap_data.size();
194 fwrite(&hdr, sizeof(hdr), 1, stdout);
195 fwrite(tap_data.data(), tap_data.size(), 1, stdout);