/*********************************************
Laser Communication System Receiver File
Authors: Keith Carter, Michael Muccio
Cornell University, Electrical and Computer Engineering
ECE 476, Spring 2003

This program is used to program a Mega32 MCU to be the
receiver for a serial voice data laser communication
system.  It receives serial data and blasts received
bytes out PORTB to a DAC.

Chip type           : ATmega32
Program type        : Application
Clock frequency     : 16.000000 MHz
Memory model        : Small
Internal SRAM size  : 2048
External SRAM size  : 0
Data Stack size     : 512
*********************************************/

#include <mega32.h>
#include <stdio.h>
#include <delay.h>  

//set baud to 27.7 kbps
#define baudnum 36
#define halfbaudnum 18

//global variables
char bitcnt;	// bit counter
char Rxbyte;	// received data
char sb;		// number of stop bits (1, 2, ...)
char k;        // debugging counter

//the data receive subroutine
void get(void); 

//Receive Byte
void get(void)
{    
	Rxbyte = 0x00;        //clear receive byte
	
	bitcnt=9+sb;          //initialize bit counter
	
	k=0;                  //initialize debug counter     
	
	//while loop waits for start bit
	while(PIND.0 != 0)
	{
		k=k+1;// hang out	
	}
	
	//delay to middle of start bit            
	delay_us(halfbaudnum);
	
	//while loop samples at middle of bits
	//stops at bitcnt of 2 to avoid shifting 
	//in stop bit
	while(bitcnt>2)  
	{
		delay_us(baudnum);      //1 bit delay 
		
		Rxbyte=Rxbyte>>1;       //shift receive byte right 1
		
		//sample bit
		//move value to MSB of receive byte
		if (PIND.0)
		{
			Rxbyte=Rxbyte | 0b10000000;		
		}
		else
		{
			Rxbyte=Rxbyte & 0b01111111;
		}
		
		bitcnt--;            //decrement bitcnt, 1 bit received
	}
	
	//blast received byte out PORTB		
     PORTB = Rxbyte;
}

void main(void)
{
	DDRD=0b00000010;      //direction for UART pins
	DDRB=0xff;            //direction for output port
	
	sb=1;  // set to 1 stop bit
	
	//infinite loop constantly calls get() to receive bytes
	while (1)
	{
	   //receive bytes
        get();
        
        //delay 1 bit to get past stop bit
        delay_us(baudnum);
	}
}