fskmodem_float.h File Reference

FSK Modem Support. More...

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Data Structures
struct	fsk_data

Macros
#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.

Macro Definition Documentation

NCOLA

#define NCOLA   0x4000

Definition at line 32 of file fskmodem_float.h.

Referenced by demodulator().

PARITY_EVEN

#define PARITY_EVEN   1

Definition at line 28 of file fskmodem_float.h.

PARITY_NONE

#define PARITY_NONE   0

Definition at line 27 of file fskmodem_float.h.

PARITY_ODD

#define PARITY_ODD   2

Definition at line 29 of file fskmodem_float.h.

Function Documentation

fsk_serial()

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

Definition at line 224 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;
}