+++ /dev/null
-#include <stdio.h>
-#include <string.h>
-#include <math.h>
-#include <unistd.h>
-#include <assert.h>
-#include <vector>
-#include <algorithm>
-
-#define LANCZOS_RADIUS 30
-#define BUFSIZE 4096
-#define HYSTERESIS_LIMIT 3000
-#define SAMPLE_RATE 44100
-#define C64_FREQUENCY 985248
-#define TAP_RESOLUTION 8
-
-#define SYNC_PULSE_START 1000
-#define SYNC_PULSE_END 15000
-#define SYNC_PULSE_LENGTH 380.0
-#define SYNC_TEST_TOLERANCE 1.10
-
-struct tap_header {
- char identifier[12];
- char version;
- char reserved[3];
- unsigned int data_len;
-};
-
-double sinc(double x)
-{
- if (fabs(x) < 1e-6) {
- return 1.0f - fabs(x);
- } else {
- return sin(x) / x;
- }
-}
-
-#if 1
-double weight(double x)
-{
- if (fabs(x) > LANCZOS_RADIUS) {
- return 0.0f;
- }
- return sinc(M_PI * x) * sinc(M_PI * x / LANCZOS_RADIUS);
-}
-#else
-double weight(double x)
-{
- if (fabs(x) > 1.0f) {
- return 0.0f;
- }
- return 1.0f - fabs(x);
-}
-#endif
-
-double interpolate(const std::vector<short> &pcm, double i)
-{
- int lower = std::max<int>(ceil(i - LANCZOS_RADIUS), 0);
- int upper = std::min<int>(floor(i + LANCZOS_RADIUS), pcm.size() - 1);
- double sum = 0.0f;
-
- for (int x = lower; x <= upper; ++x) {
- sum += pcm[x] * weight(i - x);
- }
- return sum;
-}
-
-// between [x,x+1]
-double find_zerocrossing(const std::vector<short> &pcm, int x)
-{
- if (pcm[x] == 0) {
- return x;
- }
- if (pcm[x + 1] == 0) {
- return x + 1;
- }
-
- assert(pcm[x + 1] > 0);
- assert(pcm[x] < 0);
-
- double lower = x;
- double upper = x + 1;
- while (upper - lower > 1e-6) {
- double mid = 0.5f * (upper + lower);
- if (interpolate(pcm, mid) > 0) {
- upper = mid;
- } else {
- lower = mid;
- }
- }
-
- return 0.5f * (upper + lower);
-}
-
-struct pulse {
- double time; // in seconds from start
- double len; // in seconds
-};
-
-int main(int argc, char **argv)
-{
- std::vector<short> pcm;
-
- while (!feof(stdin)) {
- short buf[BUFSIZE];
- ssize_t ret = fread(buf, 2, BUFSIZE, stdin);
- if (ret >= 0) {
- pcm.insert(pcm.end(), buf, buf + ret);
- }
- }
-
-#if 0
- for (int i = 0; i < LEN; ++i) {
- in[i] += rand() % 10000;
- }
-#endif
-
-#if 0
- for (int i = 0; i < LEN; ++i) {
- printf("%d\n", in[i]);
- }
-#endif
-
- std::vector<pulse> pulses; // in seconds
-
- // Find the flanks.
- int last_bit = -1;
- double last_upflank = -1;
- int last_max_level = 0;
- for (unsigned i = 0; i < pcm.size(); ++i) {
- int bit = (pcm[i] > 0) ? 1 : 0;
- if (bit == 1 && last_bit == 0 && last_max_level > HYSTERESIS_LIMIT) {
- // up-flank!
- double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
- if (last_upflank > 0) {
- pulse p;
- p.time = t;
- p.len = t - last_upflank;
- pulses.push_back(p);
- }
- last_upflank = t;
- last_max_level = 0;
- }
- last_max_level = std::max(last_max_level, abs(pcm[i]));
- last_bit = bit;
- }
-
- // Calibrate on the first ~25k pulses (skip a few, just to be sure).
- double calibration_factor = 1.0f;
- if (pulses.size() < SYNC_PULSE_END) {
- fprintf(stderr, "Too few pulses, not calibrating!\n");
- } else {
- double sum = 0.0;
- for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
- sum += pulses[i].len;
- }
- double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
- calibration_factor = SYNC_PULSE_LENGTH / mean_length;
- fprintf(stderr, "Calibrated sync pulse length: %.2f -> 380.0 (change %+.2f%%)\n",
- mean_length, 100.0 * (calibration_factor - 1.0));
-
- // Check for pulses outside +/- 10% (sign of misdetection).
- for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
- double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
- if (cycles < SYNC_PULSE_LENGTH / SYNC_TEST_TOLERANCE || cycles > SYNC_PULSE_LENGTH * SYNC_TEST_TOLERANCE) {
- fprintf(stderr, "Sync cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
- pulses[i].time, cycles);
- }
- }
-
- // Compute the standard deviation (to check for uneven speeds).
- double sum2 = 0.0;
- for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
- double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
- sum2 += (cycles - SYNC_PULSE_LENGTH) * (cycles - SYNC_PULSE_LENGTH);
- }
- double stddev = sqrt(sum2 / (SYNC_PULSE_END - SYNC_PULSE_START - 1));
- fprintf(stderr, "Sync pulse length standard deviation: %.2f cycles\n",
- stddev);
- }
-
- std::vector<char> tap_data;
- for (unsigned i = 0; i < pulses.size(); ++i) {
- double cycles = pulses[i].len * calibration_factor * C64_FREQUENCY;
- int len = lrintf(cycles / TAP_RESOLUTION);
- if (i > SYNC_PULSE_END && (cycles < 100 || cycles > 800)) {
- fprintf(stderr, "Cycle with upflank at %.6f was detected at %.0f cycles; misdetect?\n",
- pulses[i].time, cycles);
- }
- if (len <= 255) {
- tap_data.push_back(len);
- } else {
- int overflow_len = lrintf(cycles);
- tap_data.push_back(0);
- tap_data.push_back(overflow_len & 0xff);
- tap_data.push_back((overflow_len >> 8) & 0xff);
- tap_data.push_back(overflow_len >> 16);
- }
- }
-
- tap_header hdr;
- memcpy(hdr.identifier, "C64-TAPE-RAW", 12);
- hdr.version = 1;
- hdr.reserved[0] = hdr.reserved[1] = hdr.reserved[2] = 0;
- hdr.data_len = tap_data.size();
-
- fwrite(&hdr, sizeof(hdr), 1, stdout);
- fwrite(tap_data.data(), tap_data.size(), 1, stdout);
-}
projects / c64tapwav / blobdiff