Some parametrization.
authorSteinar H. Gunderson <sgunderson@bigfoot.com>
Fri, 3 May 2013 19:14:19 +0000 (21:14 +0200)
committerSteinar H. Gunderson <sgunderson@bigfoot.com>
Fri, 3 May 2013 19:14:19 +0000 (21:14 +0200)
decode.c

index 85872a0..7bbb250 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -13,6 +13,8 @@
 #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
 
@@ -144,33 +146,43 @@ int main(int argc, char **argv)
 
        // 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);
                }