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#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <pthread.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
#define POCSAG_MSG_LEN 256
#define POCSAG_ASYNC_BUF_NUMBER 12
#define POCSAG_DATA_LEN (16*16384) /* 256K */
#define POCSAG_AUTO_GAIN -100 /* Use automatic gain. */
#define POCSAG_MAX_GAIN 999999 /* Use max available gain. */
/* 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
#define IGNORE(V) ((void) V)
struct {
pthread_t reader_thread;
pthread_mutex_t data_mutex; /* Mutex to synchronize buffer access. */
pthread_cond_t data_cond; /* Conditional variable associated. */
unsigned char *data; /* Raw IQ samples buffer */
uint16_t *magnitude; /* Magnitude vector */
uint32_t data_len; /* Buffer length. */
int data_ready; /* Data ready to be processed. */
uint16_t *maglut; /* I/Q -> Magnitude lookup table. */
int exit;
/* rtlsdr */
int dev_index;
int gain;
int enable_agc;
rtlsdr_dev_t *dev;
int freq;
} Gascop;
struct pocsag_msg
{
uint32_t bits;
int nb;
int nc;
char buf[POCSAG_MSG_LEN];
};
void pocsag_msg_init(struct pocsag_msg *msg) {
msg->bits = 0;
msg->nb = 0;
msg->nc = 0;
memset(msg->buf, 0x00, POCSAG_MSG_LEN);
}
int hammingWeight(uint32_t n) {
int c;
for (c = 0; n; c++)
n &= n - 1;
return c;
}
uint8_t evenParity(uint32_t n) {
return hammingWeight(n) & 1;
}
uint32_t bchSyndrome(uint32_t data, int poly, int n, int k) {
uint32_t mask = 1 << (n - 1);
uint32_t 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;
}
uint32_t bchFix(uint32_t 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;
}
void rtlsdrCallback(unsigned char *buf, uint32_t len, void *ctx) {
IGNORE(ctx);
pthread_mutex_lock(&Gascop.data_mutex);
if (len > Gascop.data_len) len = Gascop.data_len;
memcpy(Gascop.data, buf, len);
Gascop.data_ready = 1;
pthread_cond_signal(&Gascop.data_cond);
pthread_mutex_unlock(&Gascop.data_mutex);
}
void *readerThreadEntryPoint(void *arg) {
IGNORE(arg);
rtlsdr_read_async(Gascop.dev, rtlsdrCallback, NULL,
POCSAG_ASYNC_BUF_NUMBER, Gascop.data_len);
return NULL;
}
int main(int argc, char **argv) {
IGNORE(argc);
IGNORE(argv);
printf("Gascop...\n");
exit(0);
}
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