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+/*
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+Copyright 2016 Luiz Ribeiro <luizribeiro@gmail.com>
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+
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+This program is free software: you can redistribute it and/or modify
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+it under the terms of the GNU General Public License as published by
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+the Free Software Foundation, either version 2 of the License, or
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+(at your option) any later version.
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+
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+This program is distributed in the hope that it will be useful,
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+but WITHOUT ANY WARRANTY; without even the implied warranty of
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+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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+GNU General Public License for more details.
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+
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+You should have received a copy of the GNU General Public License
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+along with this program. If not, see <http://www.gnu.org/licenses/>.
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+*/
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+
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+#include <avr/io.h>
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+#include <util/twi.h>
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+
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+#include "i2c.h"
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+
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+void i2c_set_bitrate(uint16_t bitrate_khz) {
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+ uint8_t bitrate_div = ((F_CPU / 1000l) / bitrate_khz);
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+ if (bitrate_div >= 16) {
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+ bitrate_div = (bitrate_div - 16) / 2;
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+ }
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+ TWBR = bitrate_div;
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+}
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+
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+void i2c_init(void) {
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+ // set pull-up resistors on I2C bus pins
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+ PORTC |= 0b11;
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+
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+ i2c_set_bitrate(400);
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+
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+ // enable TWI (two-wire interface)
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+ TWCR |= (1 << TWEN);
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+
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+ // enable TWI interrupt and slave address ACK
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+ TWCR |= (1 << TWIE);
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+ TWCR |= (1 << TWEA);
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+}
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+
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+uint8_t i2c_start(uint8_t address) {
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+ // reset TWI control register
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+ TWCR = 0;
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+
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+ // begin transmission and wait for it to end
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+ TWCR = (1<<TWINT) | (1<<TWSTA) | (1<<TWEN);
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+ while (!(TWCR & (1<<TWINT)));
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+
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+ // check if the start condition was successfully transmitted
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+ if ((TWSR & 0xF8) != TW_START) {
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+ return 1;
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+ }
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+
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+ // transmit address and wait
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+ TWDR = address;
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+ TWCR = (1<<TWINT) | (1<<TWEN);
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+ while (!(TWCR & (1<<TWINT)));
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+
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+ // check if the device has acknowledged the READ / WRITE mode
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+ uint8_t twst = TW_STATUS & 0xF8;
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+ if ((twst != TW_MT_SLA_ACK) && (twst != TW_MR_SLA_ACK)) {
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+ return 1;
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+ }
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+
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+ return 0;
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+}
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+
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+void i2c_stop(void) {
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+ TWCR = (1<<TWINT) | (1<<TWEN) | (1<<TWSTO);
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+}
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+
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+uint8_t i2c_write(uint8_t data) {
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+ TWDR = data;
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+
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+ // transmit data and wait
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+ TWCR = (1<<TWINT) | (1<<TWEN);
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+ while (!(TWCR & (1<<TWINT)));
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+
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+ if ((TWSR & 0xF8) != TW_MT_DATA_ACK) {
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+ return 1;
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+ }
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+
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+ return 0;
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+}
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+
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+uint8_t i2c_send(uint8_t address, uint8_t *data, uint16_t length) {
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+ if (i2c_start(address)) {
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+ return 1;
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+ }
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+
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+ for (uint16_t i = 0; i < length; i++) {
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+ if (i2c_write(data[i])) {
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+ return 1;
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+ }
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+ }
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+
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+ i2c_stop();
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+
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+ return 0;
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+}
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