/**********************************************
 * I2C library version 1
 * Intended for ATmega32U2 processor
 *
 * pins:
 *  PORT D  0 - SCL_PULL
 *  PORT D  1 - SDA_PULL
 *  PORT D  2 - SCL_READ
 *  PORT D  3 - SDA_READ

 *  PORT D  6 - LED output
 *  PORT D  7 - Switch output
 * 
 **********************************************/


#include <iom32u2.h>
#include <intrinsics.h>
#include <avr_macros.h>
#include <stdio.h>

// bits
#define BIT0 0x01
#define BIT1 0x02
#define BIT2 0x04
#define BIT3 0x08
#define BIT4 0x10
#define BIT5 0x20
#define BIT6 0x40
#define BIT7 0x80

// port D stuff
#define SCL_PULL   BIT0
#define SDA_PULL   BIT1
#define SCL_READ   BIT2
#define SDA_READ   BIT3
#define LED        BIT6
#define BUTTON     BIT7

// inputs
#define SWITCH_ON (PIND & BUTTON) == 0
#define SWITCH_OFF (PIND & BUTTON) != 0
#define SCL_IS_HIGH (PIND & SCL_READ) !=0
#define SDA_IS_HIGH (PIND & SDA_READ) !=0

// outputs
#define SCL_SET_LOW PORTD |= SCL_PULL
#define SCL_SET_HIGH PORTD &= ~SCL_PULL
#define SDA_SET_LOW PORTD |= SDA_PULL
#define SDA_SET_HIGH PORTD &= ~SDA_PULL

#define LED_ON PORTD |= LED
#define LED_OFF PORTD &= ~LED

void
i2c_usec_delay(void)
{
  __delay_cycles(8);

}


void
delay_10ms(unsigned int val)
{
  unsigned int i;
  for (i=0; i<val; i++)
  {
    __delay_cycles(25000);
  }
}

void
init(void)
{
  DDRD=0x43; // Set pin 6 (LED) and the first two pins, i.e. the SCL_PULL and SDA_PULL pins as outputs
  SDA_SET_HIGH;
  SCL_SET_HIGH;
}

void
i2c_start(void)
{
  i2c_usec_delay();
  SDA_SET_LOW;
  i2c_usec_delay();
  SCL_SET_LOW;
  i2c_usec_delay();
}

void i2c_stop(void)
{
  // SDA should already be low for us to begin the stop condition
  // SCL should already be high.
  SDA_SET_LOW;
  SCL_SET_HIGH;
  i2c_usec_delay();
  SDA_SET_HIGH;
  // lets wait longer after a stop condition
  delay_10ms(1);
}

void i2c_write(unsigned char val)
{
  unsigned char i;
  for (i=0; i<8; i++)
  {
    if (val & 0x80)
    {
      SDA_SET_HIGH;
    }
    else
    {
      SDA_SET_LOW;
    }
    i2c_usec_delay();
    SCL_SET_HIGH;
    i2c_usec_delay();
    SCL_SET_LOW;
    i2c_usec_delay();
    val <<= 1;
  }
  // ok now lets allow an ack to be received
  SDA_SET_HIGH;
  i2c_usec_delay();
  SCL_SET_HIGH;
  i2c_usec_delay();
  SCL_SET_LOW;
  i2c_usec_delay();
}
  
unsigned char
i2c_read(void)
{
  unsigned char i;
  unsigned char val=0;
  
  for (i=0; i<8; i++)
  {
    val<<=1;
    SCL_SET_HIGH;
    i2c_usec_delay();
    if (SDA_IS_HIGH)
    {
      val |= 0x01;
    }
    SCL_SET_LOW;
    i2c_usec_delay();
  }
  return val;
}