atmega_i2c.c

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/**
 * @file atmega_i2c.c
 * @ingroup i2c
 * @author Jason Duffy
 * @date 5th March 2022
 * @brief I2C communications driver for AVR MCU's.
 * @bug No known bugs. 
 * 
 * This file provides basic I2C protocol comms functionality.
 * Please note: Blocking waits are used whilst the host waits for hardware to
 * set bits in registers. 
 * 
 * The symbol F_CPU must be defined for the bus timing calculations - usually
 * defined in Makefile. 
 */
 
 
#include <avr/interrupt.h> 
 
#include "i2c.h"
 
 
/*
 * Sets pullups and initializes i2c clock to desired bus speed.
 * @param bus_speed is the desired i2c clock frequency.
 */
void init_i2c(uint32_t bus_speed)
{
  uint32_t base_frequency = (F_CPU / bus_speed);
  TWBR = (uint8_t)((base_frequency - 16) / (2 * 1)); // Prescaler of 1
  TWCR |= (1 << TWEN); // Enable I2C.
}
 
 
/*
 * Loops until the i2c message is complete, as the  hardware sets the TWINT
 * flag.
 */
void i2c_wait_for_complete(void)
{
  loop_until_bit_is_set(TWCR, TWINT);
}
 
 
/*
 * Sends a start condition (sets TWSTA).
 */
void i2c_start(void)
{
  TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWSTA);
  i2c_wait_for_complete();
}
 
 
/*
 * Sends a stop condition (sets TWSTO).
 */
void i2c_stop(void)
{
  TWCR = (1 << TWINT) | (1 << TWEN) | (1 <<TWSTO);
}
 
 
/*
 * Loads data, sends it out, waiting for completion.
 * @param data is the byte of data to be sent. 
 */
void i2c_send(uint8_t data)
{
  TWDR = data;
  TWCR = (1 << TWINT) | (1 << TWEN); // init and enable.
  i2c_wait_for_complete();
}
 
 
/*
 * Read in from slave, sending ACK when done (sets TWEA).
 * @returns The data received from the peripheral device. 
 */
uint8_t i2c_read_ack(void)
{
  TWCR = (1 << TWINT) | (1 << TWEN) | (1 << TWEA);
  i2c_wait_for_complete();
  return (TWDR);
}
 
 
/**
 * Read in from slave, sending NOACK when done (no TWEA).
 * @returns The data received from the peripheral device. 
 */
 
uint8_t i2c_read_no_ack(void)
{
  TWCR = (1 << TWINT) | (1 << TWEN);
  i2c_wait_for_complete();
  return (TWDR);
}
 
 
/*** end of file ***/