I2C.cpp

/* Copyright (C) 2014 Kristian Sloth Lauszus. All rights reserved.

 This software may be distributed and modified under the terms of the GNU
 General Public License version 2 (GPL2) as published by the Free Software
 Foundation and appearing in the file GPL2.TXT included in the packaging of
 this file. Please note that GPL2 Section 2[b] requires that all works based
 on this software must also be made publicly available under the terms of
 the GPL2 ("Copyleft").

 Contact information
 -------------------

 Kristian Sloth Lauszus
 Web      :  http://www.lauszus.com
 e-mail   :  lauszus@gmail.com
*/

#include <Arduino.h>
#include <Wire.h> // Standard Arduino I2C library

#include "I2C.h"

static const uint8_t I2C_TIMEOUT = 100; // Used to check for errors in I2C communication

void initI2c() {
  Wire.begin();
#if ARDUINO >= 157
  Wire.setClock(400000UL); // Set I2C frequency to 400kHz
#else
  TWBR = ((F_CPU / 400000UL) - 16) / 2; // Set I2C frequency to 400kHz
#endif
}

uint8_t i2cWrite(uint8_t address, uint8_t registerAddress, uint8_t data, bool sendStop /*= true*/) {
  return i2cWrite(address, registerAddress, &data, 1, sendStop); // Returns 0 on success
}

uint8_t i2cWrite(uint8_t address, uint8_t registerAddress, uint8_t *data, uint8_t length, bool sendStop /*= true*/) {
  Wire.beginTransmission(address);
  Wire.write(registerAddress);
  Wire.write(data, length);
  uint8_t rcode = Wire.endTransmission(sendStop); // Returns 0 on success
  if (rcode) {
    Serial.print(F("i2cWrite failed: "));
    Serial.println(rcode);
  }
  return rcode; // See: http://arduino.cc/en/Reference/WireEndTransmission
}

uint8_t i2cRead(uint8_t address, uint8_t registerAddress, uint8_t *data, uint8_t nbytes) {
  uint32_t timeOutTimer;
  Wire.beginTransmission(address);
  Wire.write(registerAddress);
  uint8_t rcode = Wire.endTransmission(false); // Don't release the bus
  if (rcode) {
    Serial.print(F("i2cRead failed: "));
    Serial.println(rcode);
    return rcode; // See: http://arduino.cc/en/Reference/WireEndTransmission
  }

  Wire.requestFrom(address, nbytes, (uint8_t)true); // Send a repeated start and then release the bus after reading
  for (uint8_t i = 0; i < nbytes; i++) {
    if (Wire.available())
      data[i] = Wire.read();
    else {
      timeOutTimer = micros();
      while (((micros() - timeOutTimer) < I2C_TIMEOUT) && !Wire.available());
      if (Wire.available())
        data[i] = Wire.read();
      else {
        Serial.println(F("i2cRead timeout"));
        return 5; // This error value is not already taken by endTransmission
      }
    }
  }
  return 0; // Success
}