#include "i2c.h" #define TWBR_VALUE(fscl) (((F_CPU / (fscl)) - 16) / 2) #define CHECK_TIMEOUT (4) // timeout in msec void init_i2c(uint32_t speed) { // Set SDA and SCL as inputs with pullup (Arduino A4/A5 pins) DDRC &= ~((1 << PC4) | (1 << PC5)); PORTC |= (1 << PC4) | (1 << PC5); // Set TWPS[1:0] = "00" (Prescaler=1) TWSR = 0x00; // Set TWI Bit Rate Register TWBR = TWBR_VALUE(speed); } uint8_t i2c_wait_for_data_complete() { uint8_t timeout = CHECK_TIMEOUT; // Wait until the TWINT bit in TWCR goes HIGH while (!(TWCR & (1 << TWINT))) { if (timeout == 0) { return 1; // timeout occurred } timeout--; _delay_ms(1); } return 0; // ok } uint8_t i2c_send_start() { // Enable TWI, clear TWINT bit and send START condition TWCR = (1 << TWINT) | (1 << TWSTA) | (1 << TWEN); // Wait for end of data transmission if (i2c_wait_for_data_complete()) { return 1; // timeout } // Check if the start condition was successfully transmitted if ((TWSR & TW_STATUS_MASK) != TW_START) { return 1; // Return with start condition error } return 0; // ok } // Start I2C transmission uint8_t i2c_start_transmission(uint8_t addr) { // Send I2C start condition if (i2c_send_start()) { return 1; // return with start condition error } // Load the first byte (slave address + R/W bit) into data register TWDR = addr; // Start transmission of the first byte TWCR = (1 << TWINT) | (1 << TWEN); // Wait for end of data transmission if (i2c_wait_for_data_complete()) { return 2; // Return with TWI data tranmission error } // Check if the device has acknowledged if ( (addr & 1) == TW_WRITE ) { if ((TWSR & TW_STATUS_MASK) != TW_MT_SLA_ACK) { return 3; // Return with NACK error (No ACK received) } } else { if ((TWSR & TW_STATUS_MASK) != TW_MR_SLA_ACK) { return 4; // Return with NACK error (No ACK received) } } return 0; // ok } inline void i2c_send_stop(void) { // Send I2C stop condition TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTO); } void i2c_end_transmission(void) { // Stop I2C transmission by sending stop condition i2c_send_stop(); } // Write a data byte and check the ACK bit uint8_t i2c_write(uint8_t data) { // Load the data byte into data register TWDR = data; // Start I2C transmission of data TWCR = (1 << TWINT) | (1 << TWEN); // Wait for end of I2C data transmission if (i2c_wait_for_data_complete()) { return 1; // Return with TWI data transmission error } if ((TWSR & TW_STATUS_MASK) != TW_MT_DATA_ACK) { return 1; // Return with NACK error (No ACK received) } return 0; } // Read a data byte from slave and send ACK or NACK uint8_t i2c_read(uint8_t *data, uint8_t ack) { TWCR = (1 << TWINT) | (1 << TWEN) | (ack ? (1 << TWEA) : 0); if (i2c_wait_for_data_complete()) { return 1; // Return with TWI data reception error } *data = TWDR; // Save the received data byte return 0; // ok } // Read a data byte from a specific register address uint8_t i2c_read_reg(uint8_t addr, uint8_t reg_addr) { uint8_t data = 0; // Send the start condition i2c_send_start(); // Write the register address i2c_write((addr << 1) | TW_WRITE); // TW_WRITE is 0. i2c_write(reg_addr); // Send the repeated start condition i2c_send_start(); // Read one data byte from the slave device i2c_write((addr << 1) | TW_READ); // TW_READ is 1. i2c_read(&data, 0 /*no ack*/); // Send the STOP condition i2c_send_stop(); return data; }