From 9a4bbd988d9c24f56275c2c21e030d08f5c9d861 Mon Sep 17 00:00:00 2001 From: "Steinar H. Gunderson" Date: Fri, 3 May 2013 21:14:19 +0200 Subject: [PATCH] Some parametrization. --- decode.c | 26 +++++++++++++++++++------- 1 file changed, 19 insertions(+), 7 deletions(-) diff --git a/decode.c b/decode.c index 85872a0..7bbb250 100644 --- 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 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); } -- 2.39.2