#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
// Calibrate on the first ~25k pulses (skip a few, just to be sure).
double calibration_factor = 1.0f;
- if (pulses.size() < 20000) {
+ if (pulses.size() < SYNC_PULSE_END) {
fprintf(stderr, "Too few pulses, not calibrating!\n");
} else {
double sum = 0.0;
- for (int i = 1000; i < 26000; ++i) {
+ for (int i = SYNC_PULSE_START; i < SYNC_PULSE_END; ++i) {
sum += pulses[i].len;
}
- double mean_length = C64_FREQUENCY * sum / 25000.0f;
+ double mean_length = C64_FREQUENCY * sum / (SYNC_PULSE_END - SYNC_PULSE_START);
calibration_factor = SYNC_PULSE_LENGTH / mean_length;
- fprintf(stderr, "Cycle length: %.2f -> 380.0 (change %+.2f%%)\n",
+ 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 = 1000; i < 25000; ++i) {
+ 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 > 15000 && (cycles < 100 || cycles > 800)) {
+ 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);
}