/*
 * 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 "DMD.h"
#if defined(ARDUINO) && ARDUINO >= 100
#include <Arduino.h>
#else
#include <WProgram.h>
#endif
#include <pins_arduino.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <string.h>
#include <stdlib.h>

/**
 * \class DMD DMD.h <DMD.h>
 * \brief Handle large dot matrix displays composed of LED's.
 *
 * This class is designed for use with
 * <a href="http://www.freetronics.com/dmd">Freetronics Large Dot Matrix
 * Displays</a>.  These displays have 512 LED's arranged in a 32x16 matrix
 * and controlled by an SPI interface.  The displays are available in
 * red, blue, green, yellow, and white variations (for which this class
 * always uses the constant \ref White regardless of the physical color).
 *
 * \section dmd_drawing Drawing
 *
 * DMD inherits from Bitmap so that any of the drawing functions in that
 * class can be used to draw directly to dot matrix displays.  The following
 * example initializes a single display panel and draws a rectangle and a
 * circle into it at setup time:
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * void setup() {
 *     display.drawRect(5, 2, 27, 13);
 *     display.drawCircle(16, 8, 4);
 * }
 * \endcode
 *
 * The display must be updated frequently from the application's main loop:
 *
 * \code
 * void loop() {
 *     display.loop();
 * }
 * \endcode
 *
 * \section dmd_interrupts Interrupt-driven display refresh
 *
 * The loop() method simplifies updating the display from the application's
 * main loop but it can sometimes be inconvenient to arrange for it to be
 * called regularly, especially if the application wishes to use
 * <tt>delay()</tt> or <tt>delayMicroseconds()</tt>.
 *
 * DMD provides an asynchronous display update mechanism using Timer1
 * interrupts.  The application turns on interrupts using enableTimer1()
 * and then calls refresh() from the interrupt service routine:
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * ISR(TIMER1_OVF_vect)
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     display.enableTimer1();
 * }
 * \endcode
 *
 * If Timer1 is already in use by some other part of your application,
 * then Timer2 can be used as an alternative interrupt source:
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * ISR(TIMER2_OVF_vect)
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     display.enableTimer2();
 * }
 * \endcode
 *
 * DMD can also be used with third-party timer libraries such as
 * <a href="http://code.google.com/p/arduino-timerone/downloads/list">TimerOne</a>:
 *
 * \code
 * #include <DMD.h>
 * #include <TimerOne.h>
 *
 * DMD display;
 *
 * void refreshDisplay()
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     Timer1.initialize(5000);
 *     Timer1.attachInterrupt(refreshDisplay);
 * }
 * \endcode
 *
 * \section dmd_double_buffer Double buffering
 *
 * When using interrupts, the system can sometimes exhibit "tearing" artifacts
 * where half-finished images are displayed because an interrupt fired in
 * the middle of a screen update.
 *
 * This problem can be alleviated using double buffering: all rendering is done
 * to an off-screen buffer that is swapped onto the screen once it is ready
 * for display.  Rendering then switches to the other buffer that is now
 * off-screen.  The following example demonstrates this:
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * ISR(TIMER1_OVF_vect)
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     display.setDoubleBuffer(true);
 *     display.enableTimer1();
 * }
 *
 * void loop() {
 *     updateDisplay();
 *     display.swapBuffers();
 *     delay(50);   // Delay between frames.
 * }
 *
 * void updateDisplay() {
 *     // Draw the new display contents into the off-screen buffer.
 *     display.clear();
 *     ...
 * }
 * \endcode
 *
 * The downside of double buffering is that it uses twice as much main memory
 * to manage the contents of the screen.
 *
 * \section dmd_multi Multiple panels
 *
 * Multiple panels can be daisy-chained together using ribbon cables.
 * If there is a single row of panels, then they must be connected
 * to the Arduino board as follows:
 *
 * \image html dmd-4x1.png
 *
 * If there are multiple rows of panels, then alternating rows are
 * flipped upside-down so that the short ribbon cables provided by
 * Freetronics reach (this technique is thanks to Chris Debenham; see
 * http://www.adebenham.com/category/arduino/dmd/ for more details):
 *
 * \image html dmd-4x2.png
 *
 * This technique can be repeated for as many rows as required, with the
 * bottom row always right-way-up:
 *
 * \image html dmd-4x3.png
 *
 * DMD automatically takes care of flipping the data for panels in the
 * alternating rows.  No special action is required by the user except
 * to physically connect the panels as shown and to initialize the DMD
 * class appropriately:
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display(4, 2);   // 4 panels wide, 2 panels high
 * \endcode
 */

// Pins on the DMD connector board.
#define DMD_PIN_PHASE_LSB       6       // A
#define DMD_PIN_PHASE_MSB       7       // B
#define DMD_PIN_LATCH           8       // SCLK
#define DMD_PIN_OUTPUT_ENABLE   9       // nOE
#define DMD_PIN_SPI_SS          SS      // SPI Slave Select
#define DMD_PIN_SPI_MOSI        MOSI    // SPI Master Out, Slave In (R)
#define DMD_PIN_SPI_MISO        MISO    // SPI Master In, Slave Out
#define DMD_PIN_SPI_SCK         SCK     // SPI Serial Clock (CLK)

// Dimension information for the display.
#define DMD_NUM_COLUMNS         32      // Number of columns in a panel.
#define DMD_NUM_ROWS            16      // Number of rows in a panel.

// Refresh times.
#define DMD_REFRESH_MS          5
#define DMD_REFRESH_US          5000

/**
 * \brief Constructs a new dot matrix display handler for a display that
 * is \a widthPanels x \a heightPanels in size.
 *
 * Note: the parameters to this constructor are specified in panels,
 * whereas width() and height() are specified in pixels.
 *
 * \sa width(), height()
 */
DMD::DMD(int widthPanels, int heightPanels)
    : Bitmap(widthPanels * DMD_NUM_COLUMNS, heightPanels * DMD_NUM_ROWS)
    , _doubleBuffer(false)
    , phase(0)
    , fb0(0)
    , fb1(0)
    , displayfb(0)
    , lastRefresh(millis())
{
    // Both rendering and display are to fb0 initially.
    fb0 = displayfb = fb;

    // Initialize SPI to MSB-first, mode 0, clock divider = 2.
    pinMode(DMD_PIN_SPI_SCK, OUTPUT);
    pinMode(DMD_PIN_SPI_MOSI, OUTPUT);
    pinMode(DMD_PIN_SPI_SS, OUTPUT);
    digitalWrite(DMD_PIN_SPI_SCK, LOW);
    digitalWrite(DMD_PIN_SPI_MOSI, LOW);
    digitalWrite(DMD_PIN_SPI_SS, HIGH);
    SPCR |= _BV(MSTR);
    SPCR |= _BV(SPE);
    SPCR &= ~(_BV(DORD));   // MSB-first
    SPCR &= ~0x0C;          // Mode 0
    SPCR &= ~0x03;          // Clock divider rate 2
    SPSR |= 0x01;           // MSB of clock divider rate

    // Initialize the DMD-specific pins.
    pinMode(DMD_PIN_PHASE_LSB, OUTPUT);
    pinMode(DMD_PIN_PHASE_MSB, OUTPUT);
    pinMode(DMD_PIN_LATCH, OUTPUT);
    pinMode(DMD_PIN_OUTPUT_ENABLE, OUTPUT);
    digitalWrite(DMD_PIN_PHASE_LSB, LOW);
    digitalWrite(DMD_PIN_PHASE_MSB, LOW);
    digitalWrite(DMD_PIN_LATCH, LOW);
    digitalWrite(DMD_PIN_OUTPUT_ENABLE, LOW);
    digitalWrite(DMD_PIN_SPI_MOSI, HIGH);
}

/**
 * \brief Destroys this dot matrix display handler.
 */
DMD::~DMD()
{
    if (fb0)
        free(fb0);
    if (fb1)
        free(fb1);
    fb = 0; // Don't free the buffer again in the base class.
}

/**
 * \fn bool DMD::doubleBuffer() const
 * \brief Returns true if the display is double-buffered; false if
 * single-buffered.  The default is false.
 *
 * \sa setDoubleBuffer(), swapBuffers(), refresh()
 */

/**
 * \brief Enables or disables double-buffering according to \a doubleBuffer.
 *
 * When double-buffering is enabled, rendering operations are sent to a
 * memory buffer that isn't currently displayed on-screen.  Once the
 * application has completed the screen update, it calls swapBuffers()
 * to display the current buffer and switch rendering to the other
 * now invisible buffer.
 *
 * Double-buffering is recommended if refresh() is being called from an
 * interrupt service routine, to prevent "tearing" artifacts that result
 * from simultaneous update of a single shared buffer.
 *
 * This function will allocate memory for the extra buffer when
 * \a doubleBuffer is true.  If there is insufficient memory for the
 * second screen buffer, then this class will revert to single-buffered mode.
 *
 * \sa doubleBuffer(), swapBuffers(), refresh()
 */
void DMD::setDoubleBuffer(bool doubleBuffer)
{
    if (doubleBuffer != _doubleBuffer) {
        _doubleBuffer = doubleBuffer;
        if (doubleBuffer) {
            // Allocate a new back buffer.
            unsigned int size = _stride * _height;
            fb1 = (uint8_t *)malloc(size);

            // Clear the new back buffer and then switch to it, leaving
            // the current contents of fb0 on the screen.
            if (fb1) {
                memset(fb1, 0xFF, size);
                cli();
                fb = fb1;
                displayfb = fb0;
                sei();
            } else {
                // Failed to allocate the memory, so revert to single-buffered.
                _doubleBuffer = false;
            }
        } else if (fb1) {
            // Disabling double-buffering, so forcibly switch to fb0.
            cli();
            fb = fb0;
            displayfb = fb0;
            sei();

            // Free the unnecessary buffer.
            free(fb1);
            fb1 = 0;
        }
    }
}

/**
 * \brief Swaps the buffers that are used for rendering to the display.
 *
 * When doubleBuffer() is false, this function does nothing.
 * Otherwise the front and back rendering buffers are swapped.
 * See the description of setDoubleBuffer() for more information.
 *
 * The new rendering back buffer will have undefined contents and will
 * probably need to be re-inialized with clear() or fill() before
 * drawing to it.  The swapBuffersAndCopy() function can be used instead
 * to preserve the screen contents from one frame to the next.
 *
 * \sa swapBuffersAndCopy(), setDoubleBuffer()
 */
void DMD::swapBuffers()
{
    if (_doubleBuffer) {
        // Turn off interrupts while swapping buffers so that we don't
        // accidentally try to refresh() in the middle of this code.
        cli();
        if (fb == fb0) {
            fb = fb1;
            displayfb = fb0;
        } else {
            fb = fb0;
            displayfb = fb1;
        }
        sei();
    }
}

/**
 * \brief Swaps the buffers that are used for rendering to the display
 * and copies the former back buffer contents to the new back buffer.
 *
 * Normally when swapBuffers() is called, the new rendering back buffer
 * will have undefined contents from two frames prior and must be cleared
 * with clear() or fill() before writing new contents to it.
 * This function instead copies the previous frame into the new
 * rendering buffer so that it can be updated in-place.
 *
 * This function is useful if the screen does not change much from one
 * frame to the next.  If the screen changes a lot between frames, then it
 * is usually better to explicitly clear() or fill() the new back buffer.
 *
 * \sa swapBuffers(), setDoubleBuffer()
 */
void DMD::swapBuffersAndCopy()
{
    swapBuffers();
    if (_doubleBuffer)
        memcpy(fb, displayfb, _stride * _height);
}

/**
 * \brief Performs regular display refresh activities from the
 * application's main loop.
 *
 * \code
 * DMD display;
 *
 * void loop() {
 *     display.loop();
 * }
 * \endcode
 *
 * If you are using a timer interrupt service routine, then call
 * refresh() in response to the interrupt instead of calling loop().
 *
 * \sa refresh()
 */
void DMD::loop()
{
    unsigned long currentTime = millis();
    if ((currentTime - lastRefresh) >= DMD_REFRESH_MS) {
        lastRefresh = currentTime;
        refresh();
    }
}

// Send a single byte via SPI.
static inline void spiSend(byte value)
{
    SPDR = value;
    while (!(SPSR & _BV(SPIF)))
        ;   // Wait for the transfer to complete.
}

// Flip the bits in a byte.  Table generated by genflip.c
static const uint8_t flipBits[256] PROGMEM = {
    0x00, 0x80, 0x40, 0xC0, 0x20, 0xA0, 0x60, 0xE0, 0x10, 0x90, 0x50, 0xD0,
    0x30, 0xB0, 0x70, 0xF0, 0x08, 0x88, 0x48, 0xC8, 0x28, 0xA8, 0x68, 0xE8,
    0x18, 0x98, 0x58, 0xD8, 0x38, 0xB8, 0x78, 0xF8, 0x04, 0x84, 0x44, 0xC4,
    0x24, 0xA4, 0x64, 0xE4, 0x14, 0x94, 0x54, 0xD4, 0x34, 0xB4, 0x74, 0xF4,
    0x0C, 0x8C, 0x4C, 0xCC, 0x2C, 0xAC, 0x6C, 0xEC, 0x1C, 0x9C, 0x5C, 0xDC,
    0x3C, 0xBC, 0x7C, 0xFC, 0x02, 0x82, 0x42, 0xC2, 0x22, 0xA2, 0x62, 0xE2,
    0x12, 0x92, 0x52, 0xD2, 0x32, 0xB2, 0x72, 0xF2, 0x0A, 0x8A, 0x4A, 0xCA,
    0x2A, 0xAA, 0x6A, 0xEA, 0x1A, 0x9A, 0x5A, 0xDA, 0x3A, 0xBA, 0x7A, 0xFA,
    0x06, 0x86, 0x46, 0xC6, 0x26, 0xA6, 0x66, 0xE6, 0x16, 0x96, 0x56, 0xD6,
    0x36, 0xB6, 0x76, 0xF6, 0x0E, 0x8E, 0x4E, 0xCE, 0x2E, 0xAE, 0x6E, 0xEE,
    0x1E, 0x9E, 0x5E, 0xDE, 0x3E, 0xBE, 0x7E, 0xFE, 0x01, 0x81, 0x41, 0xC1,
    0x21, 0xA1, 0x61, 0xE1, 0x11, 0x91, 0x51, 0xD1, 0x31, 0xB1, 0x71, 0xF1,
    0x09, 0x89, 0x49, 0xC9, 0x29, 0xA9, 0x69, 0xE9, 0x19, 0x99, 0x59, 0xD9,
    0x39, 0xB9, 0x79, 0xF9, 0x05, 0x85, 0x45, 0xC5, 0x25, 0xA5, 0x65, 0xE5,
    0x15, 0x95, 0x55, 0xD5, 0x35, 0xB5, 0x75, 0xF5, 0x0D, 0x8D, 0x4D, 0xCD,
    0x2D, 0xAD, 0x6D, 0xED, 0x1D, 0x9D, 0x5D, 0xDD, 0x3D, 0xBD, 0x7D, 0xFD,
    0x03, 0x83, 0x43, 0xC3, 0x23, 0xA3, 0x63, 0xE3, 0x13, 0x93, 0x53, 0xD3,
    0x33, 0xB3, 0x73, 0xF3, 0x0B, 0x8B, 0x4B, 0xCB, 0x2B, 0xAB, 0x6B, 0xEB,
    0x1B, 0x9B, 0x5B, 0xDB, 0x3B, 0xBB, 0x7B, 0xFB, 0x07, 0x87, 0x47, 0xC7,
    0x27, 0xA7, 0x67, 0xE7, 0x17, 0x97, 0x57, 0xD7, 0x37, 0xB7, 0x77, 0xF7,
    0x0F, 0x8F, 0x4F, 0xCF, 0x2F, 0xAF, 0x6F, 0xEF, 0x1F, 0x9F, 0x5F, 0xDF,
    0x3F, 0xBF, 0x7F, 0xFF
};

/**
 * \brief Refresh the display.
 *
 * This function must be called at least once every 5 milliseconds
 * for smooth non-flickering update of the display.  It is usually
 * called by loop(), but can also be called in response to a
 * timer interrupt.
 *
 * If this function is called from an interrupt service routine,
 * then it is recommended that double-buffering be enabled with
 * setDoubleBuffer() to prevent "tearing" artifacts that result
 * from simultaneous update of a single shared buffer.
 *
 * \sa loop(), setDoubleBuffer(), enableTimer1()
 */
void DMD::refresh()
{
    // Bail out if there is a conflict on the SPI bus.
    if (!digitalRead(DMD_PIN_SPI_SS))
        return;

    // Transfer the data for the next group of interleaved rows.
    int stride4 = _stride * 4;
    uint8_t *data0;
    uint8_t *data1;
    uint8_t *data2;
    uint8_t *data3;
    bool flipRow = ((_height & 0x10) == 0);
    for (int y = 0; y < _height; y += 16) {
        if (!flipRow) {
            // The panels in this row are the right way up.
            data0 = displayfb + _stride * (y + phase);
            data1 = data0 + stride4;
            data2 = data1 + stride4;
            data3 = data2 + stride4;
            for (int x = _stride; x > 0; --x) {
                spiSend(*data3++);
                spiSend(*data2++);
                spiSend(*data1++);
                spiSend(*data0++);
            }
            flipRow = true;
        } else {
            // The panels in this row are upside-down and reversed.
            data0 = displayfb + _stride * (y + 16 - phase) - 1;
            data1 = data0 - stride4;
            data2 = data1 - stride4;
            data3 = data2 - stride4;
            for (int x = _stride; x > 0; --x) {
                spiSend(pgm_read_byte(&(flipBits[*data3--])));
                spiSend(pgm_read_byte(&(flipBits[*data2--])));
                spiSend(pgm_read_byte(&(flipBits[*data1--])));
                spiSend(pgm_read_byte(&(flipBits[*data0--])));
            }
            flipRow = false;
        }
    }

    // Latch the data from the shift registers onto the actual display.
    digitalWrite(DMD_PIN_OUTPUT_ENABLE, LOW);
    digitalWrite(DMD_PIN_LATCH, HIGH);
    digitalWrite(DMD_PIN_LATCH, LOW);
    if (phase & 0x02)
        digitalWrite(DMD_PIN_PHASE_MSB, HIGH);
    else
        digitalWrite(DMD_PIN_PHASE_MSB, LOW);
    if (phase & 0x01)
        digitalWrite(DMD_PIN_PHASE_LSB, HIGH);
    else
        digitalWrite(DMD_PIN_PHASE_LSB, LOW);
    digitalWrite(DMD_PIN_OUTPUT_ENABLE, HIGH);
    phase = (phase + 1) & 0x03;
}

/**
 * \brief Enables Timer1 overflow interrupts for updating this display.
 *
 * The application must also provide an interrupt service routine for
 * Timer1 that calls refresh():
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * ISR(TIMER1_OVF_vect)
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     display.enableTimer1();
 * }
 * \endcode
 *
 * If timer interrupts are being used to update the display, then it is
 * unnecessary to call loop().
 *
 * \sa refresh(), disableTimer1(), enableTimer2(), setDoubleBuffer()
 */
void DMD::enableTimer1()
{
    // Number of CPU cycles in the display's refresh period.
    unsigned long numCycles = (F_CPU / 2000000) * DMD_REFRESH_US;

    // Determine the prescaler to be used.
    #define TIMER1_RESOLUTION  65536UL
    uint8_t prescaler;
    if (numCycles < TIMER1_RESOLUTION) {
        // No prescaling required.
        prescaler = _BV(CS10);
    } else if (numCycles < TIMER1_RESOLUTION * 8) {
        // Prescaler = 8.
        prescaler = _BV(CS11);
        numCycles >>= 3;
    } else if (numCycles < TIMER1_RESOLUTION * 64) {
        // Prescaler = 64.
        prescaler = _BV(CS11) | _BV(CS10);
        numCycles >>= 6;
    } else if (numCycles < TIMER1_RESOLUTION * 256) {
        // Prescaler = 256.
        prescaler = _BV(CS12);
        numCycles >>= 8;
    } else if (numCycles < TIMER1_RESOLUTION * 1024) {
        // Prescaler = 1024.
        prescaler = _BV(CS12) | _BV(CS10);
        numCycles >>= 10;
    } else {
        // Too long, so set the maximum timeout.
        prescaler = _BV(CS12) | _BV(CS10);
        numCycles = TIMER1_RESOLUTION - 1;
    }

    // Configure Timer1 for the period we want.
    TCCR1A = 0;
    TCCR1B = _BV(WGM13);
    uint8_t saveSREG = SREG;
    cli();
    ICR1 = numCycles;
    SREG = saveSREG;    // Implicit sei() if interrupts were on previously.
    TCCR1B = (TCCR1B & ~(_BV(CS12) | _BV(CS11) | _BV(CS10))) | prescaler;

    // Turn on the Timer1 overflow interrupt.
    TIMSK1 |= _BV(TOIE1);
}

/**
 * \brief Disables Timer1 overflow interrupts.
 *
 * \sa enableTimer1()
 */
void DMD::disableTimer1()
{
    // Turn off the Timer1 overflow interrupt.
    TIMSK1 &= ~_BV(TOIE1);
}

/**
 * \brief Enables Timer2 overflow interrupts for updating this display.
 *
 * The application must also provide an interrupt service routine for
 * Timer2 that calls refresh():
 *
 * \code
 * #include <DMD.h>
 *
 * DMD display;
 *
 * ISR(TIMER2_OVF_vect)
 * {
 *     display.refresh();
 * }
 *
 * void setup() {
 *     display.enableTimer2();
 * }
 * \endcode
 *
 * If timer interrupts are being used to update the display, then it is
 * unnecessary to call loop().
 *
 * \sa refresh(), disableTimer2(), enableTimer1(), setDoubleBuffer()
 */
void DMD::enableTimer2()
{
    // Configure Timer2 for the period we want.  With the prescaler set
    // to 128, then 256 increments of Timer2 gives roughly 4 ms between
    // overflows on a system with a 16 MHz clock.  We adjust the prescaler
    // accordingly for other clock frequencies.
    TCCR2A = 0;
    if (F_CPU >= 32000000)
        TCCR2B = _BV(CS22) | _BV(CS21); // Prescaler = 256
    else if (F_CPU >= 16000000)
        TCCR2B = _BV(CS22) | _BV(CS20); // Prescaler = 128
    else if (F_CPU >= 8000000)
        TCCR2B = _BV(CS22);             // Prescaler = 64
    else
        TCCR2B = _BV(CS21) | _BV(CS20); // Prescaler = 32

    // Reset Timer2 to kick off the process.
    TCNT2 = 0;

    // Turn on the Timer2 overflow interrupt (also turn off OCIE2A and OCIE2B).
    TIMSK2 = _BV(TOIE2);
}

/**
 * \brief Disables Timer2 overflow interrupts.
 *
 * \sa enableTimer2()
 */
void DMD::disableTimer2()
{
    // Turn off the Timer2 overflow interrupt.
    TIMSK2 &= ~_BV(TOIE2);
}

/**
 * \brief Converts an RGB value into a pixel color value.
 *
 * Returns \ref White if any of \a r, \a g, or \a b are non-zero;
 * otherwise returns \ref Black.
 *
 * This function is provided for upwards compatibility with future
 * displays that support full color.  Monochrome applications should
 * use the \ref Black and \ref White constants directly.
 */
DMD::Color DMD::fromRGB(uint8_t r, uint8_t g, uint8_t b)
{
    if (r || g || b)
        return White;
    else
        return Black;
}