#include <stdio.h>
+#include <string.h>
#include <math.h>
#include <unistd.h>
#include <assert.h>
#define LANCZOS_RADIUS 30
#define BUFSIZE 4096
-#define HYSTERESIS_LIMIT 1000
+#define HYSTERESIS_LIMIT 3000
+#define SAMPLE_RATE 44100
+#define C64_FREQUENCY 985248
+#define TAP_RESOLUTION 8
+
+#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)
{
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;
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 (int i = 0; i < pcm.size(); ++i) {
+ 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) * (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() < 20000) {
+ fprintf(stderr, "Too few pulses, not calibrating!\n");
+ } else {
+ double sum = 0.0;
+ for (int i = 1000; i < 26000; ++i) {
+ sum += pulses[i].len;
+ }
+ double mean_length = C64_FREQUENCY * sum / 25000.0f;
+ calibration_factor = SYNC_PULSE_LENGTH / mean_length;
+ fprintf(stderr, "Cycle 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 = 1000; i < 25000; ++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);
+ }
+ }
+ }
+
+ 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 > 15000 && (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);
}