Raspberry Pi to Arduino communication using I2C and interrupts.

RPi2c.ino

/*
 * RPi2c - test i2c communication between an Arduino and a Raspberry Pi.
 *
 * Copyright (c) 2013 Carlos Rodrigues <cefrodrigues@gmail.com>
 *
 * Permission is hereby granted, free of charge, to any person obtaining a copy
 * of this software and associated documentation files (the "Software"), to deal
 * in the Software without restriction, including without limitation the rights
 * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
 * copies of the Software, and to permit persons to whom the Software is
 * furnished to do so, subject to the following conditions:
 *
 * The above copyright notice and this permission notice shall be included in
 * all copies or substantial portions of the Software.
 *
 * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
 * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
 * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
 * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
 * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
 * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
 * THE SOFTWARE.
 */


#include <Wire.h>


static const char intPin = 8;
static const char ledPin = 9;
static const char sensorPin = A0;

short ledValue = 0;
short sensorCurr = 0;
short sensorPrev = -10;


void setup()
{
  pinMode(intPin, OUTPUT);
  pinMode(ledPin, OUTPUT);
  
  Wire.begin(0x03);
  Wire.onReceive(receiveEvent);
  Wire.onRequest(requestEvent);
}


void loop() {
  sensorCurr = 0;  
  
  // Take a few samples and average the results to avoid jitter...
  for (int i = 0; i < 10; i++) {
    sensorCurr += analogRead(sensorPin);
    delay(1);
  }
  
  sensorCurr /= 10;

  // Trigger an interrupt on the RPi when the sensor changes...
  if (abs(sensorCurr - sensorPrev) > 1) {
    sensorPrev = sensorCurr;
    
    digitalWrite(intPin, HIGH);
    delay(10);
    digitalWrite(intPin, LOW);
  }
}


void receiveEvent(int bytes) {
  int operation = Wire.read();
  
  // Change the LED intensity...
  if (operation == 0x01 && bytes > 1) {
    ledValue = Wire.read();
    analogWrite(ledPin, ledValue);
  }

  // Consume any remainder bytes...
  while (Wire.available()) {
    Wire.read();
  }
}


void requestEvent() {
  // Both the Arduino and RPi are little-endian, no conversion needed...
  Wire.write((uint8_t *)&sensorCurr, sizeof(sensorCurr));
}


/* EOF - RPi2c.pde */

rpi2c.py

#!/usr/bin/env python
#
# RPi2c - test i2c communication between an Arduino and a Raspberry Pi.
#
# Copyright (c) 2013 Carlos Rodrigues <cefrodrigues@gmail.com>
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
#


from __future__ import division
from __future__ import print_function


import RPi.GPIO as GPIO
import smbus
import time
import sys


I2C_BUS = 1
I2C_SLAVE = 0x03

INTERRUPT_PIN = 17


def interpolate(value, a1, a2, b1, b2):
    # Normalize the value into a 0..1 interval...
    n = float(value - a1) / float(a2 - a1)

    # Scale the normalized value to the target interval...
    return b1 + (n * (b2 - b1))


if __name__ == '__main__':
    # Initialize the interrupt pin...
    GPIO.setmode(GPIO.BCM)
    GPIO.setup(INTERRUPT_PIN, GPIO.IN)

    # Initialize the RPi I2C bus...
    i2c = smbus.SMBus(I2C_BUS)

    while 1:
        try:
            # Wait until the Arduino triggers the interrupt...
            GPIO.wait_for_edge(INTERRUPT_PIN, GPIO.RISING)

            try:
                # Get the sensor value from the Arduino (signed 16bit little-endian)...
                sensor_value = i2c.read_word_data(I2C_SLAVE, 0x00)
                sys.stdout.write("sensor: %d" % sensor_value)
            except IOError:
                sys.stderr.write("*** error: receiving sensor value ***\n")
                continue

            sys.stdout.write(" / ")

            try:
                # Map the sensor value to a [0, 255] interval...
                led_value = int(interpolate(sensor_value, 0, 1023, 0, 255))
                sys.stdout.write("led: %d\n" % led_value)

                # Send the PWM value for the LED to the Arduino...
                i2c.write_byte_data(I2C_SLAVE, 0x01, led_value)
            except IOError:
                sys.stderr.write("*** error: sending led value ***\n")

        except KeyboardInterrupt:
            GPIO.cleanup()


# vim: set expandtab ts=4 sw=4:

schematic.md

Hi carlosefr,
I have downloaded your code and it works perfectly and is a very good example indeed of connecting RPi and arduino with the I2C bus.
Br, Olav

What about any protocol? :)