/*
Copyright 2011 Lex Talionis (Lex.V.Talionis at gmail)
This program is free software: you can redistribute it 
and/or modify it under the terms of the GNU General Public 
License as published by the Free Software Foundation, 
either version 3 of the License, or (at your option) any 
later version.

This code uses pin change interrupts and timer 1 to mesure the 
time between the rise and fall of 3 channels of PPM 
(Though often called PWM, see http://www.arduino.cc/cgi-bin/yabb2/YaBB.pl?num=1253149521/all)
on a typical RC car reciver.  It could be extended to as
many channels as you like.  It uses the PinChangeInt library
to notice when the signal pin goes high and low, and the 
Timer1 library to record the time between.


*/
#include <PinChangeInt.h>    // http://playground.arduino.cc/Main/PinChangeInt
#include <PinChangeIntConfig.h>
#include <TimerOne.h>        // http://playground.arduino.cc/Code/Timer1

#define NO_PORTB_PINCHANGES //PinChangeInt setup
#define NO_PORTC_PINCHANGES    //only port D pinchanges (see: http://playground.arduino.cc/Learning/Pins)
#define PIN_COUNT 3    //number of channels attached to the reciver
#define MAX_PIN_CHANGE_PINS PIN_COUNT

#define RC_TURN 3    //arduino pins attached to the reciver
#define RC_FWD 2
#define RC_FIRE 4
byte pin[] = {RC_FWD, RC_TURN, RC_FIRE};    //for maximum efficency thise pins should be attached
unsigned int time[] = {0,0,0};                // to the reciver's channels in the order listed here

byte state=0;
byte burp=0;    // a counter to see how many times the int has executed
byte cmd=0;     // a place to put our serial data
byte i=0;       // global counter for tracking what pin we are on

void setup() {
    Serial.begin(115200);
    Serial.print("PinChangeInt ReciverReading test");
    Serial.println();            //warm up the serial port

    Timer1.initialize(2200);    //longest pulse in PPM is usally 2.1 milliseconds,
                                //pick a period that gives you a little headroom.
    Timer1.stop();                //stop the counter
    Timer1.restart();            //set the clock to zero

    for (byte i=0; i<3; i++)
    {
        pinMode(pin[i], INPUT);     //set the pin to input
        digitalWrite(pin[i], HIGH); //use the internal pullup resistor
    }
    PCintPort::attachInterrupt(pin[i], rise,RISING); // attach a PinChange Interrupt to our first pin
}

void loop() {
    cmd=Serial.read();        //while you got some time gimme a systems report
    if (cmd=='p')
    {
        Serial.print("time:\t");
        for (byte i=0; i<PIN_COUNT;i++)
        {
            Serial.print(i,DEC);
            Serial.print(":");
            Serial.print(time[i],DEC);
            Serial.print("\t");
        }
        Serial.print(burp, DEC);
        Serial.println();
/*      Serial.print("\t");
        Serial.print(clockCyclesToMicroseconds(Timer1.pwmPeriod), DEC);
        Serial.print("\t");
        Serial.print(Timer1.clockSelectBits, BIN);
        Serial.print("\t");
        Serial.println(ICR1, DEC);*/
    }
    cmd=0;
    switch (state)
    {
        case RISING: //we have just seen a rising edge
            PCintPort::detachInterrupt(pin[i]);
            PCintPort::attachInterrupt(pin[i], fall, FALLING); //attach the falling end
            state=255;
            break;
        case FALLING: //we just saw a falling edge
            PCintPort::detachInterrupt(pin[i]);
            i++;                //move to the next pin
            i = i % PIN_COUNT;  //i ranges from 0 to PIN_COUNT
            PCintPort::attachInterrupt(pin[i], rise,RISING);
            state=255;
            break;
        /*default:
            //do nothing
            break;*/
    }
}

void rise()        //on the rising edge of the currently intresting pin
{
    Timer1.restart();        //set our stopwatch to 0
    Timer1.start();            //and start it up
    state=RISING;
//  Serial.print('r');
    burp++;
}

void fall()        //on the falling edge of the signal
{
    state=FALLING;
    time[i]=readTimer1();    // read the time since timer1 was restarted
//  time[i]=Timer1.read();    // The function below has been ported into the
                            // the latest TimerOne class, if you have the
                            // new Timer1 lib you can use this line instead
    Timer1.stop();
//  Serial.print('f');
}

unsigned long readTimer1()        //returns the value of the timer in microseconds
{                                    //rember! phase and freq correct mode counts 
                                    //up to ICR1 then down again
    unsigned int tmp=TCNT1;
    char scale=0;
    switch (Timer1.clockSelectBits)
    {
    case 1:// no prescalse
        scale=0;
        break;
    case 2:// x8 prescale
        scale=3;
        break;
    case 3:// x64
        scale=6;
        break;
    case 4:// x256
        scale=8;
        break;
    case 5:// x1024
        scale=10;
        break;
    }
    while (TCNT1==tmp) //if the timer has not ticked yet
    {
        //do nothing -- max delay here is ~1023 cycles
    }
    tmp = (  (TCNT1>tmp) ? (tmp) : (ICR1-TCNT1)+ICR1  );//if we are counting down add the top value
                                                        //to how far we have counted down
    return ((tmp*1000L)/(F_CPU /1000L))<<scale;
}