#include "header.h"

#define TWI_PRESCALE_VALUE	1											// can be 1, 4, 16, 64
#define TWI_FREQ			100000UL									// 100kHz I2C
#define SLAVE_ADDRESS		0x38										// doc AHT20, 7.3 : address of thermistor

void i2c_init(void) {
    TWSR = TWI_PRESCALE_SET(TWI_PRESCALE_VALUE);						// 22.9.3 : (Status Register) set prescaler
    TWBR = ((F_CPU / TWI_FREQ) - 16) / (2 * TWI_PRESCALE_VALUE);		// 22.9.1 : (Bit Rate Register) set SCL frequency (formula from datasheet, 22.5.2)
}

void i2c_start(void) {
    TWCR = SEND_START_CONDITION;										// 22.9.2 : (Control Register) send Start condition (22.7.1) ! writting 1 to TWINT clears it (set it to 0)
    while (!(TEST(TWCR, TWINT)));										// p225 example code : Wait for TWINT Flag set. This indicates that the START condition has been transmitted

	uint8_t status = TWSR & 0b11111000;									// Table 22-2. Status codes for Master Transmitter Mode
    if (status != TW_START && status != TW_REP_START) {
        TWCR = SEND_STOP_CONDITION;
        return;
    }
}

void i2c_stop(void) {
    TWCR = SEND_STOP_CONDITION;											// 22.9.2 : send stop condition
}