www.pudn.com > slow.zip > fsktx.C

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	fskrx.c 
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/* Modem for MIPS   AJF	  January 1995 
   FSK transmit routines */ 
 
#include  
#include  
#include  
 
#include "modem.h" 
 
struct fskinfo 
  { int bps;			/* Tx bit rate	*/ 
    float f0, f1;		/* Tx tone freqs */ 
  }; 
 
static fskinfo fskinfo[] = 
  { {  300, 1180.0,  980.0 },	/* V21o */ 
    {  300, 1850.0, 1650.0 },	/* V21a */ 
    {	75,  450.0,  390.0 },	/* V23o */ 
    { 1200, 2100.0, 1300.0 },	/* V23a */ 
  }; 
 
static sinegen *sgen = NULL;	/* statically init'ed */ 
 
static float tone0, tone1; 
static int bitlen; 
static uchar prevbits; 
 
static void putoctet(uchar), pbit(int); 
 
 
global void inittx_fsk(vmode mode) 
  { unless (mode >= 0 && mode < 4) giveup("Bug! bad mode %d in fsk tx init", mode); 
    if (sgen == NULL) sgen = new sinegen(0.0);	/* once-only initialization */ 
    tone0 = fskinfo[mode].f0; 
    tone1 = fskinfo[mode].f1; 
    bitlen = SAMPLERATE / fskinfo[mode].bps;	/* num. samples in one bit */ 
    prevbits = 0; 
  } 
 
global void putasync(int n)			/* asynchronous output */ 
  { uint un = (n >= 0) ? (n << 1) | 0x200 :	/* add start bit, 1 stop bit */ 
			 0x3ff;			/* send mark bits while idle */ 
    until (un == 0) { pbit(un & 1); un >>= 1; } 
  } 
 
global void putsync(int x)			/* synchronous output */ 
  { if (x == HDLC_FLAG) putoctet(0x7e); 
    else if (x == HDLC_ABORT) putoctet(0x7f); 
    else 
      { uchar n = x; 
	for (int i = 0; i < 8; i++) 
	  { pbit(n >> 7); 
	    if ((prevbits & 0x1f) == 0x1f) pbit(0); /* bit-stuffing */ 
	    n <<= 1; 
	  } 
      } 
  } 
 
static void putoctet(uchar n) 
  { for (int i=0; i < 8; i++) { pbit(n >> 7); n <<= 1; } 
  } 
 
static void pbit(int bit) 
  { sgen -> setfreq(bit ? tone1 : tone0); 
    for (int i = 0; i < bitlen; i++) 
      { float val = sgen -> fnext(); 
	outsample(val); 
      } 
    prevbits = (prevbits << 1) | bit; 
  }