RFout1MHzV1_02.ino
#include <NMEAGPS.h>
#include <SoftwareSerial.h>
SoftwareSerial gpsPort(2, 3); // RX, TX
#define LEDIndicator1 5  //LED indicator for GPS Lock on pin A3
#define FIXOut 4         //Pin Out at IDC. Indicator for GPS Lock on pin 4
#define LDO_Enable A3    //GPS Voltage regulator Enable on pin A0
boolean GPSOK;
const char softwareversion[] = "1.02" ; //Version of this program, sent to serialport at startup
NMEAGPS  gps; // This parses the GPS characters
gps_fix  fix; // This holds on to the latest values



//--------------------------  SETUP -----------------------

void setup()
{
  Serial.begin(9600);
  while (!Serial)
    ;
  
  Serial.print(F("Zachtek GPS referenced RF, Software version: "));
  Serial.println(softwareversion);
   
   pinMode(LDO_Enable, OUTPUT); // Set Voltage Regulator Enable pin as output.
   digitalWrite(LDO_Enable, HIGH); //Turn on 3.1V Power supply for the Ublox GPS module
   Serial.println (F("Turning on Voltage Regulator for GPS module"));
   pinMode(LEDIndicator1, OUTPUT); // Set GPS Lock  LED pin as output.
   pinMode(FIXOut, OUTPUT);        // Set GPS Lock line as output.
   digitalWrite(LEDIndicator1, LOW); //Turn off Lock LED 
   digitalWrite(FIXOut, LOW);        //Go low on Lock line 
   delay(500);//Wait for GPSmodule to complete it's power on.
   gpsPort.begin(9600);
   GPSOK=true;
  
   //Program GPS to output RF
   if (setGPS_OutputFreq1MHz()) {
    Serial.println ("GPS Initialized to output RF at 1MHz");
    Serial.println ("Initialization is complete.");
    Serial.println ("");
    GPSOK=true; 
  }
  else
  {
    Serial.println ("Error! Could not program GPS!"); 
    GPSOK=false;  
  }
}

//--------------------------




//--------------------------  Main loop -----------------------
void loop()
{
  while (gps.available( gpsPort )) {
    fix = gps.read();
    if (fix.valid.location && fix.valid.date && fix.valid.time) 
      {
      Serial.print( F("Location: ") );  
      digitalWrite(LEDIndicator1, HIGH);   // turn the LED on 
      digitalWrite(FIXOut, HIGH);          // Set Lock Line high  
      Serial.print( fix.latitude(), 6 );
      Serial.print( ',' );
      Serial.print( fix.longitude(), 6 );
      Serial.println();
  
    }
    else
    {
      if (GPSOK) { //If the GPS is connected but not locked then short blink
        digitalWrite(LEDIndicator1, HIGH);   // turn the LED on 
        digitalWrite(FIXOut, LOW);          // Set Lock Line low 
        delay(100); 
        digitalWrite(LEDIndicator1, LOW);    // turn the LED off   
        Serial.println(F("Waiting for GPS fix")); 
      }  
    }
  }
}


//--------------------------

bool setGPS_OutputFreq100kHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0xA0, 0x86, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0xEF, 0x00, 0x00, 0x00, 0x20, 0x1B };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}

bool setGPS_OutputFreq1MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x40, 0x42, 0x0F, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0xEF, 0x00, 0x00, 0x00, 0x8A, 0x8B };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}

bool setGPS_OutputFreq2MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x80, 0x84, 0x1E, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0xEF, 0x00, 0x00, 0x00, 0x1B, 0x7F };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}


bool setGPS_OutputFreq4MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x00, 0x00, 0x00, 0x32, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x00, 0x09, 0x3D, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0xEF, 0x00, 0x00, 0x00, 0x3F, 0x8C };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}

//8MHz is the highest low-jitter frequency possible
bool setGPS_OutputFreq8MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x00, 0x12, 0x7A, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0x6F, 0x00, 0x00, 0x00, 0xD4, 0x28 };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}

//10 MHz is very jittery. Numbers that can be done with an integer division from 48MHz will produce
//the lowest jitter so 16 ,12 ,8 ,6 ,4 ,2 and 1 MHz is low jitter but 10MHz is not
//If 10MHz low jitter is needed then one option is to output 2MHz and then filter out the 5th overtone arriving at 10MHz in that way.
bool setGPS_OutputFreq10MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x80, 0x96, 0x98, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0x6F, 0x00, 0x00, 0x00, 0xF6, 0x10 };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}

//16MHz is above the specs for lUblox Neo-6, only included for experiments. 
//This will not produce as clean Square wave.
bool setGPS_OutputFreq16MHz()
{
 int gps_set_sucess=0;
 uint8_t setOutputFreq[] = {
 0xB5, 0x62, 0x06, 0x31, 0x20, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00,
 0x00, 0x00, 0x00, 0x24, 0xF4, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x80, 0x00, 0x00,
 0x00, 0x00, 0x6F, 0x00, 0x00, 0x00, 0x60, 0x12 };

 sendUBX(setOutputFreq, sizeof(setOutputFreq)/sizeof(uint8_t));
 gps_set_sucess=getUBX_ACK(setOutputFreq);
 //Serial.println("Set output Freq Done");
 return gps_set_sucess;
}


void sendUBX(uint8_t *MSG, uint8_t len) {
 gpsPort.flush();
 gpsPort.write(0xFF);
 _delay_ms(500);
 for(int i=0; i<len; i++) {
 gpsPort.write(MSG[i]);
 }
}

boolean getUBX_ACK(uint8_t *MSG) {
 uint8_t b;
 uint8_t ackByteID = 0;
 uint8_t ackPacket[10];
 unsigned long startTime = millis();
 
// Construct the expected ACK packet
 ackPacket[0] = 0xB5; // header
 ackPacket[1] = 0x62; // header
 ackPacket[2] = 0x05; // class
 ackPacket[3] = 0x01; // id
 ackPacket[4] = 0x02; // length
 ackPacket[5] = 0x00;
 ackPacket[6] = MSG[2]; // ACK class
 ackPacket[7] = MSG[3]; // ACK id
 ackPacket[8] = 0; // CK_A
 ackPacket[9] = 0; // CK_B
 
// Calculate the checksums
 for (uint8_t ubxi=2; ubxi<8; ubxi++) {
 ackPacket[8] = ackPacket[8] + ackPacket[ubxi];
 ackPacket[9] = ackPacket[9] + ackPacket[8];
 }
 
  while (1) {  // Test for success
    if (ackByteID > 9) {
      // All packets in order!
      return true;
    }
 
  // Timeout if no valid response in 3 seconds
  if (millis() - startTime > 3000) {
    return false;
  }
 
  // Make sure data is available to read
  if (gpsPort.available()) {
    b = gpsPort.read();
    // Check that bytes arrive in sequence as per expected ACK packet
    if (b == ackPacket[ackByteID]) {
      ackByteID++;
    }
    else {
      ackByteID = 0; // Reset and look again, invalid order
    }//else
  }//If
 }//While
}//getUBX_ACK