com.pi4j.wiringpi.SoftPwm Maven / Gradle / Ivy

package com.pi4j.wiringpi;

/*
 * #%L
 * **********************************************************************
ORGANIZATION  :  Pi4J
PROJECT       :  Pi4J :: Java Library (Core)
FILENAME      :  SoftPwm.java

This file is part of the Pi4J project. More information about
this project can be found here:  http://www.pi4j.com/
**********************************************************************
 * %%
 * Copyright (C) 2012 - 2018 Pi4J
 * %%
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU Lesser General Public License as
 * published by the Free Software Foundation, either version 3 of the
 * License, or (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Lesser Public License for more details.
 *
 * You should have received a copy of the GNU General Lesser Public
 * License along with this program.  If not, see
 * .
 * #L%
 */


import com.pi4j.util.NativeLibraryLoader;

/**
 * 
 * WiringPi includes a software-driven PWM handler capable of outputting a PWM signal on any of the
 * Raspberry Pi's GPIO pins.
 * 
 *
 * 
 * There are some limitations. To maintain a low CPU usage, the minimum pulse width is 100uS. That
 * combined with the default suggested range of 100 gives a PWM frequency of 100Hz. You can lower
 * the range to get a higher frequency, at the expense of resolution, or increase to get more
 * resolution, but that will lower the frequency. If you change the pulse-width in the drive code,
 * then be aware that at delays of less than 100uS wiringPi does it in a software loop, which means
 * that CPU usage will rise dramatically, and controlling more than one pin will be almost
 * impossible.
 * 
 *
 * 
 * Also note that while the routines run themselves at a higher and real-time priority, Linux can
 * still affect the accuracy of the generated signal.
 * 
 *
 * 
 * However, within these limitations, control of a light/LED or a motor is very achievable.
 * 
 *
 * 
 *  You must initialize wiringPi with one of wiringPiSetup() or wiringPiSetupGpio() functions
 * beforehand. wiringPiSetupSys() is not fast enough, so you must run your programs with sudo. 
 * 
 *
 * 
 * Before using the Pi4J library, you need to ensure that the Java VM in configured with access to
 * the following system libraries:
 * 

 * pi4j
 * wiringPi
 * pthread
 * 
 *  This library depends on the wiringPi native system library.
 (developed by
 * Gordon Henderson @ http://wiringpi.com/)
 * 
 * 
 *
 * @see http://www.pi4j.com/
 * @see http://wiringpi.com/reference/software-pwm-library/
 * @author Robert Savage (http://www.savagehomeautomation.com)
 */
public class SoftPwm {

    // private constructor
    private SoftPwm() {
        // forbid object construction
    }

    static {
        // Load the platform library
        NativeLibraryLoader.load("libpi4j.so");
    }

    /**
     * int softPwmCreate (int pin, int initialValue, int pwmRange);
     *
     * 
     * This creates a software controlled PWM pin. You can use any GPIO pin and the pin numbering
     * will be that of the wiringPiSetup function you used. Use 100 for the pwmRange, then the value
     * can be anything from 0 (off) to 100 (fully on) for the given pin.
     * 
     *
     * @see http://wiringpi.com/reference/software-pwm-library/
     *
     * @param pin The GPIO pin to use as a PWM pin.
     *            
     * @param value The value to initialize the PWM pin (between 0 (off) to 100 (fully
     *            on))
     * @param range The maximum range. Use 100 for the pwmRange.
     * @return The return value is 0 for success. Anything else and you should check the global
     *         errno variable to see what went wrong.
     */
    public static native int softPwmCreate(int pin, int value, int range);

    /**
     * void softPwmWrite (int pin, int value);
     *
     * 
     * This updates the PWM value on the given pin. The value is checked to be in-range and pins
     * that haven't previously been initialized via softPwmCreate will be silently ignored.
     * 
     *
     * @see http://wiringpi.com/reference/software-pwm-library/
     *
     * @param pin The GPIO pin to use as a PWM pin.
     * @param value The value to initialize the PWM pin (between 0 (off) to 100 (fully
     *            on))
     */
    public static native void softPwmWrite(int pin, int value);

    /**
     /**
     * void softPwmStop (int pin);
     *
     * 
     * This stops the software emulated PWM driver/thread for the given pin.
     * 
     *
     * @see http://wiringpi.com/reference/software-pwm-library/>     *
     * @param pin The GPIO pin to use as a PWM pin.
     */
    public static native void softPwmStop(int pin);
}