fskmodem_float.h File Reference

FSK Modem Support. More...

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Data Structures
struct	fsk_data
Defines
#define	NCOLA   0x4000
#define	PARITY_EVEN   1
#define	PARITY_NONE   0
#define	PARITY_ODD   2
Functions
int	fsk_serial (fsk_data *fskd, short *buffer, int *len, int *outbyte)

---

Detailed Description

FSK Modem Support.

Note:

Includes code and algorithms from the Zapata library.

Definition in file fskmodem_float.h.

---

Define Documentation

#define NCOLA   0x4000

Definition at line 32 of file fskmodem_float.h.

Referenced by demodulator().

#define PARITY_EVEN   1

Definition at line 28 of file fskmodem_float.h.

#define PARITY_NONE   0

Definition at line 27 of file fskmodem_float.h.

#define PARITY_ODD   2

Definition at line 29 of file fskmodem_float.h.

---

Function Documentation

int fsk_serial	(	fsk_data *	fskd,
		short *	buffer,
		int *	len,
		int *	outbyte
	)

Definition at line 226 of file fskmodem_float.c.

Referenced by callerid_feed(), callerid_feed_jp(), and tdd_feed().

{
   int a;
   int i,j,n1,r;
   int samples = 0;
   int olen;

   switch (fskd->state) {
      /* Pick up where we left off */
   case STATE_SEARCH_STARTBIT2:
      goto search_startbit2;
   case STATE_SEARCH_STARTBIT3:
      goto search_startbit3;
   case STATE_GET_BYTE:
      goto getbyte;
   }
   /* We await for start bit  */
   do {
      /* this was jesus's nice, reasonable, working (at least with RTTY) code
      to look for the beginning of the start bit. Unfortunately, since TTY/TDD's
      just start sending a start bit with nothing preceding it at the beginning
      of a transmission (what a LOSING design), we cant do it this elegantly */
      /*
      if (demodulator(zap,&x1)) return(-1);
      for (;;) {
         if (demodulator(zap,&x2)) return(-1);
         if (x1>0 && x2<0) break;
         x1 = x2;
      }
      */
      /* this is now the imprecise, losing, but functional code to detect the
      beginning of a start bit in the TDD sceanario. It just looks for sufficient
      level to maybe, perhaps, guess, maybe that its maybe the beginning of
      a start bit, perhaps. This whole thing stinks! */
      if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
         return -1;
      samples++;
      for (;;) {
search_startbit2:
         if (*len <= 0) {
            fskd->state  =  STATE_SEARCH_STARTBIT2;
            return 0;
         }
         samples++;
         if (demodulator(fskd, &fskd->x2, GET_SAMPLE))
            return(-1);
#if 0
         printf("x2  =  %5.5f ", fskd->x2);
#endif
         if (fskd->x2 < -0.5)
            break;
      }
search_startbit3:
      /* We await for 0.5 bits before using DPLL */
      i = fskd->spb/2;
      if (*len < i) {
         fskd->state = STATE_SEARCH_STARTBIT3;
         return 0;
      }
      for (; i>0; i--) {
         if (demodulator(fskd, &fskd->x1, GET_SAMPLE))
            return(-1);
#if 0
         printf("x1 = %5.5f ", fskd->x1);
#endif
         samples++;
      }

      /* x1 must be negative (start bit confirmation) */

   } while (fskd->x1 > 0);
   fskd->state = STATE_GET_BYTE;

getbyte:

   /* Need at least 80 samples (for 1200) or
      1320 (for 45.5) to be sure we'll have a byte */
   if (fskd->nbit < 8) {
      if (*len < 1320)
         return 0;
   } else {
      if (*len < 80)
         return 0;
   }
   /* Now we read the data bits */
   j = fskd->nbit;
   for (a = n1 = 0; j; j--) {
      olen = *len;
      i = get_bit_raw(fskd, buffer, len);
      buffer += (olen - *len);
      if (i == -1)
         return(-1);
      if (i)
         n1++;
      a >>= 1;
      a |= i;
   }
   j = 8-fskd->nbit;
   a >>= j;

   /* We read parity bit (if exists) and check parity */
   if (fskd->parity) {
      olen = *len;
      i = get_bit_raw(fskd, buffer, len);
      buffer += (olen - *len);
      if (i == -1)
         return(-1);
      if (i)
         n1++;
      if (fskd->parity == 1) {   /* parity=1 (even) */
         if (n1&1)
            a |= 0x100;    /* error */
      } else {       /* parity=2 (odd) */
         if (!(n1&1))
            a |= 0x100; /* error */
      }
   }

   /* We read STOP bits. All of them must be 1 */

   for (j = fskd->nstop;j;j--) {
      r = get_bit_raw(fskd, buffer, len);
      if (r == -1)
         return(-1);
      if (!r)
         a |= 0x200;
   }

   /* And finally we return  */
   /* Bit 8 : Parity error */
   /* Bit 9 : Framming error*/

   *outbyte = a;
   fskd->state = STATE_SEARCH_STARTBIT;
   return 1;
}