cylon/lib/io/digital-pin.js

/*
 * Linux IO DigitalPin
 * cylonjs.com
 *
 * Copyright (c) 2013-2014 The Hybrid Group
 * Licensed under the Apache 2.0 license.
*/

"use strict";

var FS = require('fs'),
    EventEmitter = require('events').EventEmitter;

var Utils = require('../utils');

var GPIO_PATH = "/sys/class/gpio";

var GPIO_READ = "in";
var GPIO_WRITE = "out";

var HIGH = 1;
var LOW = 0;

// DigitalPin class offers an interface with the Linux GPIO system present in
// single-board computers such as a Raspberry Pi, or a BeagleBone
var DigitalPin = module.exports = function DigitalPin(opts) {
  this.pinNum = opts.pin.toString();
  this.status = 'low';
  this.ready = false;
  this.mode = opts.mode;
};

Utils.subclass(DigitalPin, EventEmitter);

DigitalPin.prototype.connect = function(mode) {
  if (this.mode == null) {
    this.mode = mode;
  }

  FS.exists(this._pinPath(), function(exists) {
    exists ? this._openPin() : this._createGPIOPin();
  }.bind(this));
};

DigitalPin.prototype.close = function() {
  FS.writeFile(this._unexportPath(), this.pinNum, function(err) {
    this._closeCallback(err);
  }.bind(this));
};

DigitalPin.prototype.closeSync = function() {
  FS.writeFileSync(this._unexportPath(), this.pinNum);
  this._closeCallback(false);
};

DigitalPin.prototype.digitalWrite = function(value) {
  if (this.mode !== 'w') {
    this._setMode('w');
  }

  this.status = value === 1 ? 'high' : 'low';

  FS.writeFile(this._valuePath(), value, function(err) {
    if (err) {
      this.emit('error', "Error occurred while writing value " + value + " to pin " + this.pinNum);
    } else {
      this.emit('digitalWrite', value);
    }
  }.bind(this));

  return value;
};

// Public: Reads the digial pin's value periodicly on a supplied interval,
// and emits the result or an error
//
// interval - time (in milliseconds) to read from the pin at
//
// Returns the defined interval
DigitalPin.prototype.digitalRead = function(interval) {
  if (this.mode !== 'r') { this._setMode('r'); }

  Utils.every(interval, function() {
    FS.readFile(this._valuePath(), function(err, data) {
      if (err) {
        var error = "Error occurred while reading from pin " + this.pinNum;
        this.emit('error', error);
      } else {
        var readData = parseInt(data.toString());
        this.emit('digitalRead', readData);
      }
    }.bind(this));
  }.bind(this));
};

DigitalPin.prototype.setHigh = function() {
  return this.digitalWrite(1);
};

DigitalPin.prototype.setLow = function() {
  return this.digitalWrite(0);
};

DigitalPin.prototype.toggle = function() {
  return (this.status === 'low') ? this.setHigh() : this.setLow();
};

// Creates the GPIO file to read/write from
DigitalPin.prototype._createGPIOPin = function() {
  FS.writeFile(this._exportPath(), this.pinNum, function(err) {
    if (err) {
      this.emit('error', 'Error while creating pin files');
    } else {
      this._openPin();
    }
  }.bind(this));
};

DigitalPin.prototype._openPin = function() {
  this._setMode(this.mode, true);
  this.emit('open');
};

DigitalPin.prototype._closeCallback = function(err) {
  if (err) {
    this.emit('error', 'Error while closing pin files');
  } else {
    this.emit('close', this.pinNum);
  }
};

// Sets the mode for the GPIO pin by writing the correct values to the pin reference files
DigitalPin.prototype._setMode = function(mode, emitConnect) {
  if (emitConnect == null) { emitConnect = false; }

  this.mode = mode;

  var data = (mode === 'w') ? GPIO_WRITE : GPIO_READ;

  FS.writeFile(this._directionPath(), data, function(err) {
    this._setModeCallback(err, emitConnect);
  }.bind(this));
};

DigitalPin.prototype._setModeCallback = function(err, emitConnect) {
  if (err) {
    return this.emit('error', "Setting up pin direction failed");
  }

  this.ready = true;

  if (emitConnect) {
    this.emit('connect', this.mode);
  }
};

DigitalPin.prototype._directionPath = function() {
  return this._pinPath() + "/direction";
};

DigitalPin.prototype._valuePath = function() {
  return this._pinPath() + "/value";
};

DigitalPin.prototype._pinPath = function() {
  return GPIO_PATH + "/gpio" + this.pinNum;
};

DigitalPin.prototype._exportPath = function() {
  return GPIO_PATH + "/export";
};

DigitalPin.prototype._unexportPath = function() {
  return GPIO_PATH + "/unexport";
};