www.pudn.com > slow.zip > v29tx.C

/********************************************************* 
********************************************************** 
	v29tx.c 
********************************************************** 
**********************************************************/ 
/* Modem for MIPS   AJF	  January 1995 
   V.29 transmit routines */ 
 
#include  
 
#include  
#include  
#include  
#include  
#include  
 
#include "modem.h" 
#include "coder.h" 
 
static float shapetab[2*SYMBLEN+1] = 
  { /* Raised cosine pulse shaping with Beta = 0.5; square-root, with x/sinx compensation */ 
    +1.1510798492, +0.9848450677, +0.5795790021, +0.1495226763, 
    -0.1156411181, -0.1625782395, -0.0750914609, +0.0185567369, 
    +0.0448950047, 
  }; 
 
static bool inited = false;	/* statically init'ed */ 
 
static sinegen *carrier; 
static coroutine *bitco; 
static scrambler *scr; 
static encoder *enc; 
static traininggen *trn; 
 
static void bitloop(), sendsymbol(complex); 
 
 
global void inittx_v29() 
  { unless (inited) 
      { /* perform once-only initialization */ 
	carrier = new sinegen(1700.0); 
	bitco = new coroutine(bitloop); 
	scr = new scrambler(GPC); 
	enc = new encoder; 
	trn = new traininggen; 
	inited = true; 
      } 
    bitco -> reset(); 
    for (int i = 0; i < 144; i++) putbit(1);	/* scrambled 1s */ 
  } 
 
global void putbit(int bit)	/* V.29 bit output (7200 bit/s) */ 
  { callco(bitco, bit); 
  } 
 
static void bitloop() 
  { trn -> reset(); 
    for (int bc = SEG_1; bc < SEG_4; bc++) sendsymbol(trn -> get(bc));	/* send training sequence */ 
    scr -> reset(); enc -> reset(); 
    for (;;) 
      { int bits = 0; 
	for (int i = 0; i < 3; i++) 
	  { int b = callco(currentco -> creator); 
	    bits = (bits << 1) | scr -> fwd(b); 
	  } 
	sendsymbol(enc -> encode(bits)); 
      } 
  } 
 
static void sendsymbol(complex z) 
  { static complex a0 = 0.0, a1 = 0.0, a2 = 0.0, a3 = 0.0; 
    for (int k = 0; k < SYMBLEN; k++) 
      { /* baseband pulse shaping */ 
	complex s = shapetab[SYMBLEN + k]   * a0 
		  + shapetab[k]		    * a1 
		  + shapetab[SYMBLEN - k]   * a2 
		  + shapetab[2*SYMBLEN - k] * a3; 
	/* modulate onto carrier */ 
	complex cz = carrier -> cnext(); 
	outsample(0.2 * (s.re*cz.re + s.im*cz.im)); 
      } 
    a0 = a1; a1 = a2; a2 = a3; a3 = z; 
  }