Charlieplex.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 "Charlieplex.h"
#if defined(ARDUINO) && ARDUINO >= 100
#include <Arduino.h>
#else
#include <WProgram.h>
#endif
#include <stdlib.h>
#include <string.h>

Charlieplex::Charlieplex(const uint8_t *pins, uint8_t numPins)
    : _count(((int)numPins) * (numPins - 1))
    , _lastTime(micros())
    , _currentIndex(-1)
    , _pwmPhase(0xC0)
{
    // Determine the best hold time for 50 Hz refresh when all LED's
    // are lit.  Divide it again by 4 (to get 200 Hz) to manage the
    // simulated PWM in refresh().
    _holdTime = 20000 / _count / 4;

    // Allocate the pin arrays and populate them.  Doing this now makes
    // refresh() more efficient later, at the expense of some memory.
    _pins1 = (uint8_t *)malloc(_count);
    _pins2 = (uint8_t *)malloc(_count);
    int n = 0;
    for (uint8_t pass = 1; pass < numPins; ++pass) {
        for (uint8_t pin = 0; pin < (numPins - pass); ++pin) {
            _pins1[n] = _pins2[n + 1] = pins[pin];
            _pins2[n] = _pins1[n + 1] = pins[pin + pass];
            n += 2;
        }
    }

    // Allocate space for the LED value array and zero it.
    _values = (uint8_t *)malloc(_count);
    memset(_values, 0, _count);

    // Start with all pins configured as floating inputs (all LED's off).
    for (uint8_t pin = 0; pin < numPins; ++pin) {
        digitalWrite(pins[pin], LOW);
        pinMode(pins[pin], INPUT);
    }
}

Charlieplex::~Charlieplex()
{
    free(_pins1);
    free(_pins2);
    free(_values);
}

void Charlieplex::loop()
{
    unsigned long us = micros();
    if ((us - _lastTime) >= _holdTime) {
        _lastTime = us;
        refresh();
    }
}

void Charlieplex::refresh()
{
    // Find the next LED to be lit.
    int prevIndex = _currentIndex;
    int limit = _count;
    while (limit >= 0) {
        _currentIndex = (_currentIndex + 1) % _count;
        if (_values[_currentIndex] != 0)
            break;
        --limit;
    }
    if (limit < 0) {
        // No LED's are lit.  Turn off the previous LED and exit.
        if (prevIndex != -1) {
            digitalWrite(_pins1[prevIndex], LOW);
            digitalWrite(_pins2[prevIndex], LOW);
            pinMode(_pins1[prevIndex], INPUT);
            pinMode(_pins2[prevIndex], INPUT);
        }
        _currentIndex = -1;
        return;
    }

    // Light the current LED.
    uint8_t value = _values[_currentIndex];
    uint8_t pin1 = _pins1[_currentIndex];
    uint8_t pin2 = _pins2[_currentIndex];
    _pwmPhase += 0x40;
    if (prevIndex != _currentIndex) {
        // Turn off the previous LED.
        if (prevIndex != -1) {
            digitalWrite(_pins1[prevIndex], LOW);
            digitalWrite(_pins2[prevIndex], LOW);
            pinMode(_pins1[prevIndex], INPUT);
            pinMode(_pins2[prevIndex], INPUT);
        }

        // We simulate PWM using a phase counter because analogWrite()
        // combined with holdTime() causes too much flickering if more
        // than one LED is lit.  This reduces the PWM resolution to 1 in 4.
        pinMode(pin1, OUTPUT);
        pinMode(pin2, OUTPUT);
        if (value > _pwmPhase)
            digitalWrite(pin1, HIGH);
        else
            digitalWrite(pin1, LOW);
    } else {
        // Same LED as previous.  Since there is only a single LED
        // that is lit, we can use analogWrite() to set the PWM state.
        if (value == 255)
            digitalWrite(pin1, HIGH);
        else
            analogWrite(pin1, value);
    }
}