AVR Freaks

Hello people,

Can somebody please explain me the logic/algorithm behind this code. I could figure out a couple things but wasn't able to connect them.

This section is for BiPhase encoded data capture:

void biphase_capture(void) 
{ 
 
#ifdef DEBUG_EMDB409
  sbi(PORTA,DEC5);
#endif
  uint8_t y,delta; 
  uint16_t capt; 
  uint16_t icr = ICR1;    
 
  TCCR1B ^= (1<<ICES1);             // Switchover of sensitive ICP edge 
  capt = icr - last_capture; 
  last_capture = icr;               // counter1 is now free-running 
 
  if(capt>255) delta = 255; else delta = (uint8_t)capt; 
  if (debug_mode > 2) {  
     if(debug_mode==4) store_pulse_lenght(delta);
     else {                  
       store_pulse(delta);  
       return; 
      }
   } 
  y = 0; 
  delta += halfDataRate >> (TOLERANCE_SHIFT);   // dynamic resolution (dependent on datarate)   !!!!! >> 2 
  delta -= halfDataRate;        // always subtract datarate/2 
  if (delta > halfDataRate) {   // when longer than that, try to subtract once more 
    y++; 
    delta -= halfDataRate; 
  } 
 
  if (delta > halfDataRate) {        // check overflow of counter and range 
                                    // this check is also dynamic, depends on current datarate 
                                    // the faster datarate the more precise must the signal be 
    if (last_valid == 0) { 
      store_bit(bit_pos^1, 0);      // rtf feature 
      store_bit ( 0, 1);            // store bad bit 
      last_valid = 1;  
    } 
    bit_pos = 0; 
 
  } else { 
 
    if (y) { 
      store_bit(1, 0); 
      bit_pos = 0; 
      last_valid = 0; 
    } else { 
      if (bit_pos++) { 
        store_bit(0, 0); 
        bit_pos = 0; 
        last_valid = 0; 
      } 
    } 
  } 
 
#ifdef DEBUG_EMDB409
  cbi(PORTA,DEC5);
#endif

This section is for Manchester encoded data capture:

void manchester_capture(void) { 

#ifdef DEBUG_EMDB409
  sbi(PORTA,DEC5); //debug port set
#endif 
  uint8_t y, delta; 
  uint16_t capt; 
  uint16_t icr = ICR1; // T/C 1 input capture register
 
  edge = TCCR1B; //Timer/Counter 1 Control and Status Register
  TCCR1B = edge ^ (1<<ICES1);   //T/C 1 Control and Status Register Bit    // Switchover of sensitive ICP edge 
  capt = icr - last_capture; 
  last_capture = icr;               // counter1 is now free-running 
 
 
  if(capt>255) delta = 255; else delta = (uint8_t)capt; 
 
  if (debug_mode > 2) {  
    if(debug_mode==4) 
      store_pulse_lenght(delta);
    else {                  
      store_pulse(delta);  
      return; 
    }
  } 

  if ((first != 0) && (forward_link_type == EM4150)) {                     // according to the first pulse length, manchester decoder is synchronized  
  
    first = 0;   
    last_bit = 0; 
    capt = maxCaptureTimeLow + icr; 
    if (capt < (uint16_t)(2*halfDataRate) )  //with setup latency of about 12 RF clocks 
      bit_pos = last_bit = 1; 
    else 
      store_bit(last_bit, 0); 
    return; 
  } 
 
  y = 0; 
  delta += halfDataRate >> 2;   // dynamic resolution (dependent on datarate) 
//  delta += (halfDataRate >> TOLERANCE_SHIFT);   // dynamic resolution (dependent on datarate) 
  delta -= halfDataRate;        // always subtract datarate/2 
  if (delta > halfDataRate) {   // when longer than that, try to subtract once more 
    y++; 
    delta -= halfDataRate; 
  } 
 
  if ((delta<<1) > halfDataRate) {     // check overflow of counter and range 
                                        // this check is also dynamic, depends on current datarate 
                                        // the faster datarate the more precise must the signal be 
 
    if(last_valid == 0) {      
 
      last_bit = ((~edge)>>ICES1)&1;   // rtf feature 4026 
      store_bit(last_bit, 0);           // rtf feature 4026  
      store_bit ( 1, 1 );               // store bad bit 
      last_valid = 1; 
      bit_pos++;                        // change! 4026 
 
    } 
    last_bit = 0; 
  } else { 
 
    if (y) { 
      last_bit = ((~edge)>>ICES1)&1; 
      store_bit(last_bit, 0); 
      last_valid = 0; 
      bit_pos = 0; 
    } else { 
      if (bit_pos++) { 
        store_bit(last_bit, 0); 
        bit_pos = 0; 
        last_valid = 0; 
      } 
    } 
  } 
 
#ifdef DEBUG_EMDB409
  cbi(PORTA,DEC5);
#endif
} 

Really appreciate if someone could give me any input.

Thanks

AM