Trigger on down-flanks instead of up-flanks.

[c64tapwav] / decode.cpp

diff --git a/decode.cpp b/decode.cpp
index ca0c675e411fbddfca3037cddbbd7fc1e69083e7..1a5ee74856c5c635e37ea434213307114964be6c 100644 (file)
--- a/decode.cpp
+++ b/decode.cpp
@@ -36,11 +36,11 @@ double find_zerocrossing(const std::vector<short> &pcm, int x)
                return x + 1;
        }
 
-       assert(pcm[x + 1] > 0);
-       assert(pcm[x] < 0);
+       assert(pcm[x + 1] < 0);
+       assert(pcm[x] > 0);
 
-       double lower = x;
-       double upper = x + 1;
+       double upper = x;
+       double lower = x + 1;
        while (upper - lower > 1e-6) {
                double mid = 0.5f * (upper + lower);
                if (lanczos_interpolate(pcm, mid) > 0) {
@@ -86,18 +86,18 @@ int main(int argc, char **argv)
 
        // Find the flanks.
        int last_bit = -1;
-       double last_upflank = -1;
+       double last_downflank = -1;
        for (unsigned i = 0; i < pcm.size(); ++i) {
                int bit = (pcm[i] > 0) ? 1 : 0;
-               if (bit == 1 && last_bit == 0) {
+               if (bit == 0 && last_bit == 1) {
                        // Check if we ever go up above HYSTERESIS_LIMIT before we dip down again.
                        bool true_pulse = false;
                        unsigned j;
-                       int max_level_after = -32768;
+                       int min_level_after = 32767;
                        for (j = i; j < pcm.size(); ++j) {
-                               max_level_after = std::max<int>(max_level_after, pcm[j]);
-                               if (pcm[j] < 0) break;
-                               if (pcm[j] > HYSTERESIS_LIMIT) {
+                               min_level_after = std::min<int>(min_level_after, pcm[j]);
+                               if (pcm[j] > 0) break;
+                               if (pcm[j] < -HYSTERESIS_LIMIT) {
                                        true_pulse = true;
                                        break;
                                }
@@ -105,22 +105,22 @@ int main(int argc, char **argv)
 
                        if (!true_pulse) {
 #if 0
-                               fprintf(stderr, "Ignored up-flank at %.6f seconds due to hysteresis (%d < %d).\n",
-                                       double(i) / SAMPLE_RATE, max_level_after, HYSTERESIS_LIMIT);
+                               fprintf(stderr, "Ignored down-flank at %.6f seconds due to hysteresis (%d < %d).\n",
+                                       double(i) / SAMPLE_RATE, -min_level_after, HYSTERESIS_LIMIT);
 #endif
                                i = j;
                                continue;
                        } 
 
-                       // up-flank!
+                       // down-flank!
                        double t = find_zerocrossing(pcm, i - 1) * (1.0 / SAMPLE_RATE);
-                       if (last_upflank > 0) {
+                       if (last_downflank > 0) {
                                pulse p;
                                p.time = t;
-                               p.len = t - last_upflank;
+                               p.len = t - last_downflank;
                                pulses.push_back(p);
                        }
-                       last_upflank = t;
+                       last_downflank = t;
                }
                last_bit = bit;
        }
@@ -143,7 +143,7 @@ int main(int argc, char **argv)
                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",
+                               fprintf(stderr, "Sync cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
                                        pulses[i].time, cycles);
                        }
                }
@@ -166,7 +166,7 @@ int main(int argc, char **argv)
                fprintf(fp, "%f %f\n", pulses[i].time, cycles);
                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",
+                       fprintf(stderr, "Cycle with downflank at %.6f was detected at %.0f cycles; misdetect?\n",
                                        pulses[i].time, cycles);
                }
                if (len <= 255) {