/******************************************************************************
 Title:   serial 9600 bitbanged for a tiny26
 

 tiny26 running at 8Mhz,
 
 
 Author:   rue_mohr
 Date:     Aug 18 2016
 Software: AVR-GCC 
 Hardware: attiny26
 
    
*******************************************************************************/
#include<avr/io.h>
#include<avr/interrupt.h>


#define OUTPUT                   1
#define INPUT                    0

// Bit positions

#define SetBit(BIT, PORT)        PORT |= (1<<BIT)
#define ClearBit(BIT, PORT)      PORT &= ~(1<<BIT)
#define DefBit(BIT, PORT, VALUE) PORT &= (~(1<<BIT))|((VALUE==0?0:1)<<BIT)
#define IsHigh(BIT, PORT)       (PORT & (1<<BIT)) != 0
#define IsLow(BIT, PORT)        (PORT & (1<<BIT)) == 0
#define NOP()                    asm volatile ("nop"::)

volatile unsigned char txbuffer, status;

void initTimer(void);
void sendChar(unsigned char data);
void initSerial(void);
void TXService(void);
void Delay9600(void) ;

#define txd     1
#define serport PORTB

#define dataHigh()   SetBit(txd, serport)
#define dataLow()    ClearBit(txd, serport)


int main (void)  {
 
  DDRA = (INPUT << PA0 | INPUT << PA1 | INPUT << PA2 | INPUT << PA3 | INPUT << PA4 | INPUT << PA5 |INPUT << PA6 |INPUT << PA7);      
  DDRB = (INPUT << PB0 | OUTPUT << PB1 | INPUT << PB2 | INPUT << PB3 | INPUT << PB4 | INPUT << PB5 |INPUT << PB6 |INPUT << PB7);
      
  initSerial();
  initTimer();
  
  sei();   
                  
  while(1) {      
    sendChar('R'); while(status) ;
    sendChar('u'); while(status) ;
    sendChar('e'); while(status) ;
    sendChar(' '); while(status) ;
    sendChar('R'); while(status) ;
    sendChar('U'); while(status) ;
    sendChar('L'); while(status) ;
    sendChar('E'); while(status) ;     
    sendChar('S'); while(status) ;
    sendChar('\r'); while(status) ;
    sendChar('\n'); while(status) ;
  }
}
    
//------------------------| FUNCTIONS |------------------------



void initTimer(void) {

  TCCR1B |= ((1<<CTC1) | (1<<CS12)); // clear on match, clk/8
  OCR1A  = 103;                      // when to fire the interrupt
  OCR1C  = 103;                      // when to rollover
  TIMSK |= (1<<OCIE1A);              // and do interrupt us
  
}

ISR( TIMER1_CMPA_vect ) {
 TXService();
}


void sendChar(unsigned char data) {
 
  if (status == 0) { // burn
  
    txbuffer = data;
    status   = 10;
  
  }      
}

void initSerial(void){
  // setup the io bit
  dataHigh();
  status = 0;
}

void TXService(void){
  static unsigned char mask;
  
  switch(status) {
    case 10: // send start bit
      dataLow();
      break;
    case 9:  
      mask = 0x01;
    case 8:
    case 7:
    case 6: 
    case 5:  
    case 4:
    case 3:
    case 2: // send bit
      if (mask & txbuffer) { dataHigh(); }
      else                 { dataLow(); }
      mask <<= 1;
      break;
      
    case 1: // send stop
      dataHigh();
      break;
      
    default:
      return;
  }
  status -= 1;
  return;
}