/*  EEPROMv1
 *  Simple sketch that uses the Arduino built in EEPROM
 *  
 *  Part of the DCC Turntable Project at
 *  http://www.digitaltown.co.uk/project7ModelRailwayTurntable.php
 * 
 *  EEPROM is used to store the turntable exit positions, these are adjustable
 *  using a couple of push to contact buttons allowing positions to be turned over time.
 *  These values are stored in EEPROM so that they are updated when the Arduino restarts
 */

 //EEPROM
//system will use built in eeprom as it should not be written to very much
//it has a limited lifecycle compared to external eeprom chips.
#include "EEPROM.h"

const int eepromOffset = 200;//this is the position of the first byte stored in EEPROM
//An UNO only has 512 bytes of EEPROM, I used 200 as a value to stop all my projects using the 1st byte
//This value can be set to 0 if you have not stored data in EEPROM before

//This array holds the positions for the number 1 end of the turntable
//A default value has been put in to populate the EEPROM
int trackPositions[4] = {247, 10747, 13047, 23547}; //default positions in steps of track exits from end 1

long eepromUpdatePeriod = 60000;//60 secs between updates...also used to turn the power off
unsigned long eepromUpdateTimer;

//update the eeprom with current trackpositions
void updateeeprom() {
  int q;
  //writing 4 integer values to EEPROM
  for (q = 0; q < 4; q++) {

    //EEPROM.update used as it only writes a value if it is different to the existing value.
    //This prevents constant unrequired writes.

    //As the step postion is an integer it needs to br written across 2 locations
    //As each location can only store 1 byte
    EEPROM.update((q * 2) + eepromOffset, highByte(trackPositions[q]));
    EEPROM.update((q * 2) + eepromOffset + 1, lowByte(trackPositions[q]));
  }
  //Once we have written the values to the EEPROM we will read them back
  geteepromdata();
}

void geteepromdata() {
  int q;
  //get the 4 bytes of data
  byte getbytes[8];//2 bytes per position
  Serial.println("getbytes[]: ");
  //get the data from eeprom and store in array
  for (q = 0; q < 8; q++) {
    getbytes[q] = EEPROM.read(q + eepromOffset);
    Serial.println( getbytes[q]);
  }
  Serial.println("trackPositions[]: ");
  //now assemble the data and put into trackpositions[4]
  for (q = 0; q < 4; q++) {
    trackPositions[q] = (getbytes[q * 2] * 256) + (getbytes[(q * 2) + 1]);
    Serial.println(trackPositions[q]);
  }
}

void setup() {
  Serial.begin(9600);
  Serial.println("EEPROMv1...");
  //updateeeprom();//comment this line out once the EEPROM has been updated for the first time
  geteepromdata();
}

void loop() {
  
  //This updates the EEPROM every 60 seconds, more than enough for turntable position updates.
  if (millis() > eepromUpdateTimer) {
    //reset the time period for the next update
    eepromUpdateTimer = millis() + eepromUpdatePeriod;
    //update the eeprom
    updateeeprom();
  }

}