IRreceiver.cpp

/*
 * Copyright (C) 2012 Southern Storm Software, Pty Ltd.
 *
 * 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 "IRreceiver.h"
#if defined(ARDUINO) && ARDUINO >= 100
#include <Arduino.h>
#else
#include <WProgram.h>
#endif

static IRreceiver *receiver = 0;

void _IR_receive_interrupt(void)
{
    receiver->handleInterrupt();
}

IRreceiver::IRreceiver(int interruptNumber)
    : _system(0)
    , _systemFilter(-1)
    , started(false)
    , halfChange(false)
    , lastChange(0)
    , bits(0)
    , bitCount(0)
    , buffer(0)
    , lastBuffer(0)
{
    switch (interruptNumber) {
    case 0: default:    pin = 2; break;
    case 1:             pin = 3; break;
    case 2:             pin = 21; break;    // Arduino Mega only
    case 3:             pin = 20; break;    // Arduino Mega only
    case 4:             pin = 19; break;    // Arduino Mega only
    case 5:             pin = 18; break;    // Arduino Mega only
    }
    receiver = this;
    attachInterrupt(interruptNumber, _IR_receive_interrupt, CHANGE);
}

int IRreceiver::command()
{
    unsigned buf;

    // Read the last-delivered sequence from the buffer and clear it.
    cli();
    buf = buffer;
    buffer = 0;
    sei();

    // Bail out if no sequence or it is not for us.
    if (!buf) {
        _system = -1;
        return -1;
    }
    if (_systemFilter != -1) {
        if (((buf >> 6) & 0x1F) != _systemFilter) {
            _system = -1;
            return -1;
        }
    }

    // Extract the command.
    int cmd = buf & 0x3F;
    if ((buf & 0x1000) == 0)
        cmd += 64;

    // Is this a new command or an auto-repeat of the previous command?
    // Bit 11 will toggle whenever a new button press is started.
    if (lastBuffer == buf)
        cmd += AUTO_REPEAT;
    else
        lastBuffer = buf;
    _system = (buf >> 6) & 0x1F;
    return cmd;
}

// Number of microseconds that the signal is HIGH or LOW for
// indicating a bit.  A 1 bit is transmitted as LOW for 889us
// followed by HIGH for 889us.  A 0 bit is HIGH, then LOW.
#define IR_BIT_TIME 889

// Number of microseconds to detect a long gap in the coding
// corresponding to 2 time units HIGH or LOW.  We actually check
// for at least 1.5 time units to allow for slight variations
// in timing on different remote controls.
#define IR_LONG_BIT_TIME (889 * 6 / 4)

// Maximum timeout for a single bit.  If we don't see a rising edge
// within this time, then we have lost sync and need to restart.
#define IR_MAX_TIME (IR_BIT_TIME * 4)

// Protocol details from http://en.wikipedia.org/wiki/RC-5
void IRreceiver::handleInterrupt()
{
    bool value = digitalRead(pin);
    unsigned long currentTime = micros();
    if (!value) {
        // Rising edge (input is active-LOW)
        if (started && (currentTime - lastChange) > IR_MAX_TIME) {
            // Too long since the last received bit, so restart the process.
            started = false;
        }
        if (started) {
            // We recognize bits on the falling edges, so merely
            // adjust the "changed at last half-cycle" flag.
            if ((currentTime - lastChange) > IR_LONG_BIT_TIME) {
                // Long time since last falling edge indicates that the
                // next bit will definitely be a 1.
                halfChange = true;
            } else {
                halfChange = !halfChange;
            }
            lastChange = currentTime;
        } else {
            // Encountered the start bit - start receiving up to 14 bits.
            lastChange = currentTime;
            started = true;
            halfChange = true;
            bits = 0;
            bitCount = 14;
        }
    } else if (started) {
        // Falling edge
        if ((currentTime - lastChange) > IR_LONG_BIT_TIME) {
            // Long time since last rise indicates 1 followed by 0.
            bits = (bits << 2) | 0x02;
            --bitCount;
            halfChange = true;
        } else if (halfChange) {
            // Rise was halfway through, so falling edge indicates a 1.
            bits = (bits << 1) | 0x01;
            halfChange = false;
        } else {
            // Rise was at the start, so falling edge indicates a 0.
            bits <<= 1;
            halfChange = true;
        }
        lastChange = currentTime;
        --bitCount;
        if (bitCount <= 0) {
            // All 14 bits have been received, so deliver the value.
            started = false;
            buffer = bits;
        }
    }
}