#ifndef  F_CPU
#define F_CPU 16000000UL
#endif

#include <avr/io.h>
#include <util/twi.h>

#include "i2c.h"

#define F_SCL 100000UL		// SCL frequency
#define Prescaler 1
#define TWBR_val ((((F_CPU / F_SCL) / Prescaler) - 16 ) / 2)

void i2c_init(void)
{
	TWBR = (uint8_t) TWBR_val;
}

uint8_t i2c_start(uint8_t address)
{
	// reset TWI control register
	TWCR = 0;
	// transmit START condition 
	TWCR = (1 << TWINT) | (1 << TWSTA) | (1 << TWEN);
	// wait for end of transmission
	while (!(TWCR & (1 << TWINT))) ;

	// check if the start condition was successfully transmitted
	if ((TWSR & 0xF8) != TW_START) {
		return 1;
	}
	// load slave address into data register
	TWDR = address;
	// start transmission of address
	TWCR = (1 << TWINT) | (1 << TWEN);
	// wait for end of transmission
	while (!(TWCR & (1 << TWINT))) ;

	// check if the device has acknowledged the READ / WRITE mode
	uint8_t twst = TW_STATUS & 0xF8;
	if ((twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK))
		return 1;

	return 0;
}

uint8_t i2c_write(uint8_t data)
{
	// load data into data register
	TWDR = data;
	// start transmission of data
	TWCR = (1 << TWINT) | (1 << TWEN);
	// wait for end of transmission
	while (!(TWCR & (1 << TWINT))) ;

	if ((TWSR & 0xF8) != TW_MT_DATA_ACK) {
		return 1;
	}

	return 0;
}

uint8_t i2c_read_ack(void)
{

	// start TWI module and acknowledge data after reception
	TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWEA);
	// wait for end of transmission
	while (!(TWCR & (1 << TWINT))) ;
	// return received data from TWDR
	return TWDR;
}

uint8_t i2c_read_nack(void)
{

	// start receiving without acknowledging reception
	TWCR = (1 << TWINT) | (1 << TWEN);
	// wait for end of transmission
	while (!(TWCR & (1 << TWINT))) ;
	// return received data from TWDR
	return TWDR;
}

uint8_t i2c_transmit(uint8_t address, uint8_t * data, uint16_t length)
{
	if (i2c_start(address | I2C_WRITE))
		return 1;

	for (uint16_t i = 0; i < length; i++) {
		if (i2c_write(data[i]))
			return 1;
	}

	i2c_stop();

	return 0;
}

uint8_t i2c_receive(uint8_t address, uint8_t * data, uint16_t length)
{
	if (i2c_start(address | I2C_READ))
		return 1;

	for (uint16_t i = 0; i < (length - 1); i++) {
		data[i] = i2c_read_ack();
	}
	data[(length - 1)] = i2c_read_nack();

	i2c_stop();

	return 0;
}

uint8_t i2c_writeReg(uint8_t devaddr, uint8_t regaddr, uint8_t * data,
		     uint16_t length)
{
	if (i2c_start(devaddr | 0x00))
		return 1;

	i2c_write(regaddr);

	for (uint16_t i = 0; i < length; i++) {
		if (i2c_write(data[i]))
			return 1;
	}

	i2c_stop();

	return 0;
}

uint8_t i2c_readReg(uint8_t devaddr, uint8_t regaddr, uint8_t * data,
		    uint16_t length)
{
	if (i2c_start(devaddr))
		return 1;

	i2c_write(regaddr);

	if (i2c_start(devaddr | 0x01))
		return 1;

	for (uint16_t i = 0; i < (length - 1); i++) {
		data[i] = i2c_read_ack();
	}
	data[(length - 1)] = i2c_read_nack();

	i2c_stop();

	return 0;
}

void i2c_stop(void)
{
	// transmit STOP condition
	TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO);
}