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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.h>
#include <stdint.h>
#include <errno.h>
#include <unistd.h>
#include <math.h>
#include <sys/time.h>
#include <signal.h>
#include <fcntl.h>
#include <ctype.h>
#include "rtl-sdr.h"
/* POCSAG parameters */
#define POCSAG_ID "POCSAG"
#define POCSAG_SYM_RATE 1200
#define POCSAG_FM_DEV 4500
#define POCSAG_SPS 8
#define POCSAG_STD_SYNC 0x7cd215d8
#define POCSAG_STD_IDLE 0x7a89c197
#define POCSAG_WORDSIZE 32
#define POCSAG_SOFTTHRESHOLD 2
#define POCSAG_MAXWORD 16
/* BCH parameters */
#define POCSAG_BCH_POLY 0x769
#define POCSAG_BCH_N 31
#define POCSAG_BCH_K 21
/* POCASG states */
#define POCSAG_SEARCH_PREAMBLE_START 0
#define POCSAG_SEARCH_PREAMBLE_END 1
#define POCSAG_SYNC 2
#define POCSAG_SEARCH_SYNC 3
#define POCSAG_SYNCHED 4
int hammingWeight(int n) {
unsigned int c;
for (c = 0; n; c++)
n &= n - 1;
return c;
}
int evenParity(int n) {
return hammingWeight(n) & 1;
}
int bchSyndrome(int data, int poly, int n, int k) {
int mask = 1 << (n - 1);
int coeff = poly << (k - 1);
n = k;
int s = data >> 1;
while (n > 0) {
if (s & mask)
s ^= coeff;
n -= 1;
mask >>= 1;
coeff >>= 1;
}
if (evenParity(data))
s |= 1 << (n - k);
return s;
}
int bchFix(int data, int poly, int n, int k) {
int i, j;
for (i=0; i<32; i++) {
int t = data ^ (1 << i);
if (!bchSyndrome(t, poly, n, k))
return t;
}
for (i=0; i<32; i++) {
for (j=i+1; j<32; j++) {
int t = data ^ ((1 << i) | (1 << j));
if (!bchSyndrome(t, poly, n, k))
return t;
}
}
return data;
}
int main(int argc, char **argv) {
printf("Dumpocsag v0.1\n");
exit(0);
}
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