Add calibration support.

[c64tapwav] / decode.c

diff --git a/decode.c b/decode.c
index 993f103a597e5286989c40a3fc5ba648328bc95a..923913dea5a317ecca934ce59a0978959fc1534c 100644 (file)
--- a/decode.c
+++ b/decode.c
@@ -2,11 +2,15 @@
 #include <math.h>
 #include <unistd.h>
 #include <assert.h>
+#include <vector>
 #include <algorithm>
 
 #define LANCZOS_RADIUS 30
-#define LEN 813440
+#define BUFSIZE 4096
 #define HYSTERESIS_LIMIT 1000
+#define SAMPLE_RATE 44100
+#define C64_FREQUENCY 985248
+#define TAP_RESOLUTION 8
 
 double sinc(double x)
 {
@@ -35,38 +39,36 @@ double weight(double x)
 }
 #endif
 
-double interpolate(const short *in, double i)
+double interpolate(const std::vector<short> &pcm, double i)
 {
-       int lower = std::max(int(ceil(i - LANCZOS_RADIUS)), 0);
-       int upper = std::min(int(floor(i + LANCZOS_RADIUS)), LEN - 1);
+       int lower = std::max<int>(ceil(i - LANCZOS_RADIUS), 0);
+       int upper = std::min<int>(floor(i + LANCZOS_RADIUS), pcm.size() - 1);
        double sum = 0.0f;
 
        for (int x = lower; x <= upper; ++x) {
-               sum += in[x] * weight(i - x);
+               sum += pcm[x] * weight(i - x);
        }
        return sum;
 }
        
-short in[LEN];
-
 // between [x,x+1]
-double find_zerocrossing(int x)
+double find_zerocrossing(const std::vector<short> &pcm, int x)
 {
-       if (in[x] == 0) {
+       if (pcm[x] == 0) {
                return x;
        }
-       if (in[x + 1] == 0) {
+       if (pcm[x + 1] == 0) {
                return x + 1;
        }
 
-       assert(in[x + 1] > 0);
-       assert(in[x] < 0);
+       assert(pcm[x + 1] > 0);
+       assert(pcm[x] < 0);
 
        double lower = x;
        double upper = x + 1;
        while (upper - lower > 1e-6) {
                double mid = 0.5f * (upper + lower);
-               if (interpolate(in, mid) > 0) {
+               if (interpolate(pcm, mid) > 0) {
                        upper = mid;
                } else {
                        lower = mid;
@@ -78,7 +80,15 @@ double find_zerocrossing(int x)
 
 int main(int argc, char **argv)
 {
-       fread(in, LEN*2, 1, stdin);
+       std::vector<short> pcm;
+
+       while (!feof(stdin)) {
+               short buf[BUFSIZE];
+               ssize_t ret = fread(buf, 2, BUFSIZE, stdin);
+               if (ret >= 0) {
+                       pcm.insert(pcm.end(), buf, buf + ret);
+               }
+       }       
 
 #if 0
        for (int i = 0; i < LEN; ++i) {
@@ -91,23 +101,46 @@ int main(int argc, char **argv)
                printf("%d\n", in[i]);
        }
 #endif
+
+       std::vector<float> pulse_lengths;  // in seconds
+
+       // Find the flanks.
        int last_bit = -1;
        double last_upflank = -1;
        int last_max_level = 0;
-       for (int i = 0; i < LEN; ++i) {
-               int bit = (in[i] > 0) ? 1 : 0;
+       for (int 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(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_lengths.push_back(t - last_upflank);
                        }
                        last_upflank = t;
                        last_max_level = 0;
                }
-               last_max_level = std::max(last_max_level, abs(in[i]));
+               last_max_level = std::max(last_max_level, abs(pcm[i]));
                last_bit = bit;
        }
+
+       // Calibrate on the first ~15k pulses (skip a few, just to be sure).
+       float calibration_factor = 1.0f;
+       if (pulse_lengths.size() < 20000) {
+               fprintf(stderr, "Too few pulses, not calibrating!\n");
+       } else {
+               double sum = 0.0;
+               for (int i = 1000; i < 16000; ++i) {
+                       sum += pulse_lengths[i];
+               }
+               double mean_length = C64_FREQUENCY * sum / 15000.0f;
+               calibration_factor = 380.0 / mean_length;
+               fprintf(stderr, "Cycle length: %.2f -> 380.0 (change %+.2f%%)\n",
+                       mean_length, 100.0 * (calibration_factor - 1.0));
+       }
+
+       for (int i = 0; i < pulse_lengths.size(); ++i) {
+               int len = lrintf(pulse_lengths[i] * calibration_factor * C64_FREQUENCY / TAP_RESOLUTION);
+               //fprintf(stderr, "length: %f (0x%x)\n", t - last_upflank, len);
+               printf("0x%x\n", len);
+       }
 }