#include "msp430x20x2.h"

#define HEADER_BYTES 3
#define BITS_PER_BYTE 8
#define BYTES_PER_BLOCK 9

unsigned byte_number=0;
unsigned bit_number=0;

unsigned char byte_stream[] = "GO BEARS!";

int main( void )
{
  // Stop watchdog timer to prevent time out reset
  WDTCTL = WDTPW + WDTHOLD;

  /* 
  Setup Ports
    P1.7 : TX Enable Input
    P1.0 : TX Serial Data Output
  */
  P1OUT = 0;
  P1SEL &= ~BIT0;
  P1SEL = BIT7;
  P1DIR = 0x7f;
  
  /* 
  Clock Setup
    CPU clock: 16MHz
    ADC Clock: 16MHz/8 = 2MHz
  */
  BCSCTL1 = CALBC1_8MHZ;
  DCOCTL = CALDCO_8MHZ;
  BCSCTL2 = SELM_0+DIVM_0+DIVS_3;
  
  /* 
  ADC setup
    Repeating Single-Channel Sampling
  */
  ADC10CTL1 = INCH_7+ADC10DIV_7+CONSEQ_2+ADC10SSEL_3;
  ADC10CTL0 = SREF_0+ADC10SHT_3+ADC10ON+ADC10IE;
  
  /* 
  ADC Starts 
  */
  ADC10CTL0 |= ENC+ADC10SC+MSC;
  
  /*
  Wait for interruption and transmit
  */
  while(1){
    _BIS_SR(GIE); 
  };
 
}

#pragma vector = ADC10_VECTOR
__interrupt void adc_isr(void)
{
  
  if (ADC10MEM > 512) /* TX is enabled */
  {  
    
    switch (byte_number){
      
      case 0: /* Header-high byte 2-byte long */
        
        /* 1 is always sent */
        P1OUT |= BIT0;
        
        /* Point to the next bit */
        bit_number ++;
        
        if (bit_number == (BITS_PER_BYTE<<1)){/* This is the last bit */
          
          /* wrap the bit number */
          bit_number = 0;
          
          /* point to the next byte */
          byte_number += 2;
        }
          
        break;
        
      case 2: /* Header-low byte */
        
        /* 0 is always sent */
        P1OUT &= ~BIT0;
        
        /* Point to the next bit */
        bit_number ++;
        
        if (bit_number == BITS_PER_BYTE){/* This is the last bit */
          
          /* wrap the bit number */
          bit_number = 0;
          
          /* point to the next byte */
          byte_number ++;
        }
        
        break;
        
      default: /* Information byte */
        
        /* Wrap the bit number if a byte has been finished */
        bit_number = bit_number % BITS_PER_BYTE;
        
        /* Transmit bit stream */
        P1OUT = ((byte_stream[byte_number-HEADER_BYTES]<<(BITS_PER_BYTE-bit_number-1))&0x0080)>>(BITS_PER_BYTE-1);
        
        /* Point to the next bit */
        bit_number ++;
        
        if (bit_number == BITS_PER_BYTE){/* This is the last bit */
          
          /* wrap the bit number */
          bit_number = 0;
          
          /* point to the next byte */
          byte_number ++;
          
          if (byte_number == HEADER_BYTES+BYTES_PER_BLOCK){/* This is the last byte */
          
            /* wrap the byte number */
            byte_number = 0;
          }
        }
        
        break;
    }
    
  }
  

}