RFDecoder.cpp

00001 /*
00002    RFDecoder - Ported from the Lucas Maziero Arduino libary to decode RF controls based on chip HT6P20
00003   Copyright (c) 2011 Miguel Maldonado.  All right reserved.
00004   
00005   Project home: https://github.com/lucasmaziero/RF_HT6P20
00006 
00007   This library is free software; you can redistribute it and/or
00008   modify it under the terms of the GNU Lesser General Public
00009   License as published by the Free Software Foundation; either
00010   version 2.1 of the License, or (at your option) any later version.
00011 
00012   This library is distributed in the hope that it will be useful,
00013   but WITHOUT ANY WARRANTY; without even the implied warranty of
00014   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015   Lesser General Public License for more details.
00016 */
00017 
00018 #include "RFDecoder.h"
00019 #include "mbed.h"
00020 #include <Pulse.h>
00021 
00022 
00023 /** Class constructor.
00024  * The constructor assigns the specified pinout, attatches 
00025  * an Interrupt to the receive pin. 
00026  * @param tx Transmitter pin of the RF module.
00027  * @param rx Receiver pin of the RF module.
00028  */
00029  
00030  RFDecoder::RFDecoder(PinName tx, PinName rx) : _tx(DigitalOut(tx)), _rx(PulseInOut(rx)){
00031      RFDecoder::addressFull = NULL;     
00032      
00033      }
00034  
00035 unsigned long RFDecoder::getCode(){
00036     return(addressFull);
00037 } 
00038 
00039 bool RFDecoder::available(){
00040      static bool startbit=0;          //checks if start bit was identified
00041      static int counter;            //received bits counter: 20 of Address + 4 of Data + 4 of EndCode (Anti-Code)
00042      static unsigned long buffer;   //buffer for received data storage
00043      
00044      int dur0, dur1;                // pulses durations (auxiliary)
00045         
00046      if (!startbit) {               // Check the PILOT CODE until START BIT;
00047      dur0 = _rx.read_low_us();
00048      
00049         //If time at "0" is between 9200 us (23 cycles of 400us) and 13800 us (23 cycles of 600 us).
00050         if((dur0 > 9200) && (dur0 < 13800) && !startbit){
00051             //calculate wave length - lambda
00052             lambda_RX = (dur0 / 23);
00053             
00054             //Reset variables
00055             dur0 = 0;
00056             buffer = 0;
00057             counter = 0;
00058 
00059             startbit = true;    
00060         }
00061      }
00062      
00063      //If Start Bit is OK, then starts measure os how long the signal is level "1" and check is value is into acceptable range.
00064      if (startbit && counter < 28){
00065          ++counter;
00066 
00067          dur1 = _rx.read_high_us();
00068 
00069         if((dur1 > 0.5 * lambda_RX) && (dur1 < (1.5 * lambda_RX))){  //If pulse width at "1" is between "0.5 and 1.5 lambda", means that pulse is only one lambda, so the data is "1".     
00070           buffer = (buffer << 1) + 1;   // add "1" on data buffer
00071         }
00072         else if((dur1 > 1.5 * lambda_RX) && (dur1 < (2.5 * lambda_RX))){  //If pulse width at "1" is between "1.5 and 2.5 lambda", means that pulse is two lambdas, so the data is "0".
00073           buffer = (buffer << 1);       // add "0" on data buffer
00074         }
00075         else{
00076           startbit = false; //Reset the loop
00077         }
00078       }
00079       
00080       //Check if all 28 bits were received (20 of Address + 4 of Data + 4 of Anti-Code)
00081       if (counter==28) 
00082       { 
00083       
00084         // Check if Anti-Code is OK (last 4 bits of buffer equal "0101")
00085         if ((bitRead(buffer, 0) == 1) && (bitRead(buffer, 1) == 0) && (bitRead(buffer, 2) == 1) && (bitRead(buffer, 3) == 0)){     
00086           counter = 0;
00087           startbit = false;
00088     
00089           //Get ADDRESS COMPLETO from Buffer
00090           addressFull = buffer;
00091           
00092           //If a valid data is received, return OK
00093           return true;
00094         }
00095         else
00096         {
00097           //Reset the loop
00098           startbit = false;
00099         }
00100     
00101       }
00102       
00103       //If none valid data is received, return NULL and FALSE values 
00104       addressFull = 0; 
00105       return false;       
00106 }
00107 
00108 bool RFDecoder::bitRead( int N, int pos)
00109    {                            // pos = 7 6 5 4 3 2 1 0
00110        int b = N >> pos ;       // Shift bits
00111        b = b & 1 ;              // get only the last bit
00112        return b ;
00113    }   
00114