#include <stdio.h>
+#include <string.h>
#include <math.h>
#include <unistd.h>
#include <assert.h>
+#include <vector>
#include <algorithm>
#define LANCZOS_RADIUS 30
-#define LEN 813440
+#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)
{
}
#endif
-double interpolate(const short *in, double i)
+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)), LEN - 1);
+ 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 += in[x] * weight(i - x);
+ sum += pcm[x] * weight(i - x);
}
return sum;
}
-short in[LEN];
-
// between [x,x+1]
-double find_zerocrossing(int x)
+double find_zerocrossing(const std::vector<short> &pcm, int x)
{
- if (in[x] == 0) {
+ if (pcm[x] == 0) {
return x;
}
- if (in[x + 1] == 0) {
+ if (pcm[x + 1] == 0) {
return x + 1;
}
- assert(in[x + 1] > 0);
- assert(in[x] < 0);
+ 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(in, mid) > 0) {
+ 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)
{
- fread(in, LEN*2, 1, stdin);
+ 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) {
printf("%d\n", in[i]);
}
#endif
+
+ std::vector<pulse> pulses; // in seconds
+
+ // Find the flanks.
int last_bit = -1;
double last_upflank = -1;
- for (int i = 0; i < LEN; ++i) {
- int bit = (in[i] > 0) ? 1 : 0;
- if (bit == 1 && last_bit == 0) {
+ 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(i - 1) * (123156.0/44100.0);
+ double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
if (last_upflank > 0) {
-// fprintf(stderr, "length: %f (0x%x)\n", t - last_upflank, lrintf(t - last_upflank));
- int len = lrintf(t - last_upflank);
- printf("0x%x\n", len);
+ 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);
}