upm/src/ppd42ns/ppd42ns.cxx

/*
 * Author: Zion Orent <sorent@ics.com>
 * Copyright (c) 2014 Intel Corporation.
 *
 * 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 <iostream>
#include <string>
#include <stdexcept>
#include <stddef.h>
#include <stdio.h>
#include <time.h>
#include <math.h>
#include <sys/sysinfo.h>
#include "ppd42ns.h"

using namespace upm;

PPD42NS::PPD42NS(int pin)
{
    if ( !(m_gpio = mraa_gpio_init(pin)) ) 
      {
        throw std::invalid_argument(std::string(__FUNCTION__) +
                                    ": mraa_gpio_init() failed, invalid pin?");
        return;
      }

    mraa_gpio_dir(m_gpio, MRAA_GPIO_IN);
}

PPD42NS::~PPD42NS()
{
    mraa_gpio_close(m_gpio);
}

dustData PPD42NS::getData()
{
	dustData data;
	struct timespec printData_start={0,0};
	struct timespec printData_now={0,0};
	clock_gettime(CLOCK_MONOTONIC, &printData_start);
	clock_gettime(CLOCK_MONOTONIC, &printData_now);
	double low_pulse_occupancy = 0;
	double pulse_check_time = 30;
	
	// Keep reading dust data until 30 seconds have passed
	double start_time, end_time;
	while (m_timediff(printData_start, printData_now) < pulse_check_time)
	{
		start_time = m_timediff(printData_start, printData_now);
		end_time = pulse_check_time - start_time;
		low_pulse_occupancy += pulseIn_polyfill(0, end_time);
		clock_gettime(CLOCK_MONOTONIC, &printData_now);
	}

	// Store dust data
	double ratio = low_pulse_occupancy / (pulse_check_time * 1000 * 10.0);  // Integer percentage 0=>100
	double concentration = (1.1 * pow(ratio,3)) - (3.8 * pow(ratio, 2)) + (520 * ratio) + 0.62; // using spec sheet curve
	data.lowPulseOccupancy = (int)low_pulse_occupancy;
	data.ratio = ratio;
	data.concentration = concentration;

	return data;
}


// Mimicking Arduino's pulseIn function
//	return how long it takes a pin to go from HIGH to LOW or LOW to HIGH
double PPD42NS::pulseIn_polyfill(bool high_low_value, double end_time)
{
	struct timespec pulseIn_start={0,0};
	struct timespec pulseIn_now={0,0};
	struct timespec pulsetime_start={0,0};
	struct timespec pulsetime_end={0,0};

	int pin_val = 5; // some non-zero, non-1 number
	bool started_timing = false;
	bool ended_timing = false;
	clock_gettime(CLOCK_MONOTONIC, &pulseIn_start);

	// run through this loop until either:
	//	a) we detect a change in pulse
	//	b) we've hit 30 seconds
	while (!ended_timing && (m_timediff(pulseIn_start, pulseIn_now) < end_time))
	{
		pin_val = (bool)mraa_gpio_read(m_gpio);
		if (pin_val == high_low_value && !started_timing)
		{
			clock_gettime(CLOCK_MONOTONIC, &pulsetime_start);
			started_timing = true;
			//std::cout << "Started counting pulse change" << std::endl;
			usleep(50);
		}
		else if (started_timing && pin_val != high_low_value)
		{
			clock_gettime(CLOCK_MONOTONIC, &pulsetime_end);
			ended_timing = true;
			//std::cout << "Ended counting pulse change" << (m_timediff(pulseIn_start, pulseIn_now)) << std::endl;
		}
		else
			usleep(50);
		clock_gettime(CLOCK_MONOTONIC, &pulseIn_now);
	}

	double low_pulse_occupancy = 0;

	// if we ended due to detecting a pulse change and not due to hitting 30 seconds
	if (started_timing && ended_timing)
		low_pulse_occupancy = m_timediff(pulsetime_start, pulsetime_end);
	//std::cout << "Low pulse occupancy is " << low_pulse_occupancy << " seconds" << std::endl;

	return (low_pulse_occupancy * 1000000); // convert to microseconds
}

double PPD42NS::m_timediff(timespec time1, timespec time2)
{
	return ((double)time2.tv_sec + 1.0e-9*time2.tv_nsec) - 
			((double)time1.tv_sec + 1.0e-9*time1.tv_nsec);
}