i2c & eeprom

#define F_CPU 1000000UL
#include <stdint.h>
#include <avr/io.h>
#include <util/delay.h>
#include <avr/cpufunc.h>

#define A 0x80
#define B 0x20
#define C 0x08
#define D 0x02
#define E 0x01
#define F 0x40
#define G 0x10

#define I2C_PORT    PORTC
#define I2C_DDR     DDRC
#define I2C_PIN     PINC
#define SDA         4
#define SCL         5

uint8_t digits[16] = {
    A | B | C | D | E | F,      //0
    B | C,                      //1
    A | B | D | E | G,          //2
    A | B | C | D | G,          //3
    B | C | F | G,              //4
    A | C | D | F | G,          //5
    A | C | D | E | F | G,      //6
    A | B | C,                  //7
    A | B | C | D | E | F | G,  //8
    A | B | C | D | F | G,      //9
    A | B | C | E | F | G,      //a
    C | D | E | F | G,          //b
    A | D | E | F,              //c
    B | C | D | E | G,          //d
    A | D | E | F | G,          //e
    A | E | F | G               //f
};

void
set_led_digit(uint8_t id, uint8_t value)
{
	DDRD = 0xff;

	DDRB |= 1 << id;

	PORTB &= 0xf8;
	PORTB |= 1 << id;

	PORTD = digits[value];
}

uint8_t
i2c_get_sda()
{
    return (I2C_PIN >> SDA) & 0x01;
}

uint8_t
i2c_get_scl()
{
    return (I2C_PIN >> SCL) & 0x01;
}

void
i2c_set_scl(const uint8_t value)
{
    do {
        if (value) {
            I2C_DDR &= ~(1 << SCL);
        } else {
            I2C_DDR |= 1 << SCL;
        }
    } while (i2c_get_scl() != value);
}

void
i2c_set_sda(const uint8_t value)
{
    do {
        if (value) {
            I2C_DDR &= ~(1 << SDA);
        } else {
            I2C_DDR |= 1 << SDA;
        }
        
    } while (i2c_get_sda() != value);
}

void
i2c_start()
{
    /* pull down SDA while SCL is up */
    i2c_set_sda(1);
    i2c_set_scl(1);
    i2c_set_sda(0);
}

void
i2c_stop()
{
    /* release SDA while SCL is up */
    i2c_set_sda(0);
    i2c_set_scl(1);
    i2c_set_sda(1);
}

/* returns ACK bit */
uint8_t
i2c_write(uint8_t byte)
{
    int8_t bit_no;
    for (bit_no = 7; bit_no >= 0; bit_no--) {
        i2c_set_scl(0);
        /* put next bit on SDA */
        i2c_set_sda((byte >> bit_no) & 0x01);
        i2c_set_scl(1);
    }
    /* release SDA; let slave to be able to change it */
    i2c_set_sda(1);
    i2c_set_scl(0);
    i2c_set_scl(1);
    /* get slave ACK bit */
    return i2c_get_sda();
}

uint8_t
i2c_read(uint8_t ack)
{
    /* release SDA; let slave to be able to change it */
    i2c_set_sda(1);
    uint8_t byte = 0;
    int8_t bit_no;
    for (bit_no = 7; bit_no >= 0; bit_no--) {
        i2c_set_scl(0);
        i2c_set_scl(1);
        /* get next bit */
        byte |= i2c_get_sda() << bit_no;
    }
    i2c_set_scl(0);
    /* set ACK bit */
    i2c_set_sda(ack);
    i2c_set_scl(1);
    return byte;
}

int
main()
{   
    I2C_PORT &= ~((1 << SDA) | (1 << SCL));
    
    //const uint8_t eeprom_i2c_addr = 0b10100000;
    const uint8_t eeprom_i2c_addr = 0xa0;
    const uint16_t eeprom_memory_addr = 0x0000;
    const uint8_t eeprom_memory_value = 0x42;
    uint8_t ack = 0;
    i2c_start();
    ack |= i2c_write(eeprom_i2c_addr);
    ack |= i2c_write((uint8_t) (eeprom_memory_addr >> 8)) << 1;
    ack |= i2c_write((uint8_t) eeprom_memory_addr) << 2;
    ack |= i2c_write(eeprom_memory_value) << 3;
    i2c_stop();
    while(1) {
        set_led_digit(0, ack);
        _delay_ms(1);
    }
    
    return 0;
}