ardupilot/libraries/GPS_UBLOX/GPS_UBLOX.cpp

/*
	GPS_UBLOX.cpp - Ublox GPS library for Arduino
	Code by Jordi Muñoz and Jose Julio. DIYDrones.com
	This code works with boards based on ATMega168 / 328 and ATMega1280/2560 (Serial port 1)

	This library is free software; you can redistribute it and / or
		modify it under the terms of the GNU Lesser General Public
		License as published by the Free Software Foundation; either
		version 2.1 of the License, or (at your option) any later version.

	GPS configuration : Ublox protocol
	Baud rate : 38400
	Active messages : 
		NAV - POSLLH Geodetic Position Solution, PAGE 66 of datasheet
		NAV - VELNED Velocity Solution in NED, PAGE 71 of datasheet
		NAV - STATUS Receiver Navigation Status
			or 
		NAV - SOL Navigation Solution Information

	Methods:
		Init() : GPS Initialization
		Read() : Call this funcion as often as you want to ensure you read the incomming gps data
		
	Properties:
		Lattitude : Lattitude * 10,000,000 (long value)
		Longitude : Longitude * 10,000,000 (long value)
		Altitude :	Altitude * 100 (meters) (long value)
		Ground_speed : Speed (m / s) * 100 (long value)
		Ground_course : Course (degrees) * 100 (long value)
		NewData : 1 when a new data is received.
							You need to write a 0 to NewData when you read the data
		Fix : 1: GPS FIX, 0: No Fix (normal logic)
			
*/

#include "GPS_UBLOX.h"

#include <avr/interrupt.h>
#include "WProgram.h"


// Constructors ////////////////////////////////////////////////////////////////
GPS_UBLOX_Class::GPS_UBLOX_Class()
{
}


// Public Methods //////////////////////////////////////////////////////////////
void GPS_UBLOX_Class::Init(void)
{
	ck_a = 0;
	ck_b = 0;
	UBX_step = 0;
	NewData = 0;
	Fix = 0;
	PrintErrors = 0;
	GPS_timer = millis();	 // Restarting timer...
	// Initialize serial port
	#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
		Serial1.begin(38400);				 // Serial port 1 on ATMega1280/2560
	#else
		Serial.begin(38400);
	#endif
}

// optimization : This code don´t wait for data, only proccess the data available
// We can call this function on the main loop (50Hz loop)
// If we get a complete packet this function calls parse_ubx_gps() to parse and update the GPS info.
void GPS_UBLOX_Class::Read(void)
{
	static unsigned long GPS_timer = 0;
	byte data;
	int numc;
	
	#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)		// If AtMega1280/2560 then Serial port 1...
	numc = Serial1.available();
	#else
	numc = Serial.available();
	#endif
	if (numc > 0)
		for (int i = 0; i < numc; i++)	// Process bytes received
			{
		#if defined(__AVR_ATmega1280__) || defined(__AVR_ATmega2560__)
			data = Serial1.read();
		#else
			data = Serial.read();
		#endif
			switch(UBX_step)		 // Normally we start from zero. This is a state machine
			{
			case 0:	
				if(data == 0xB5)	// UBX sync char 1
					UBX_step++;	 // OH first data packet is correct, so jump to the next step
				break; 
			case 1:	
				if(data == 0x62)	// UBX sync char 2
					UBX_step++;	 // ooh! The second data packet is correct, jump to the step 2
				else 
					UBX_step = 0;	 // Nop, is not correct so restart to step zero and try again.		 
				break;
			case 2:
				UBX_class = data;
				ubx_checksum(UBX_class);
				UBX_step++;
				break;
			case 3:
				UBX_id = data;
				ubx_checksum(UBX_id);
				UBX_step++;
				break;
			case 4:
				UBX_payload_length_hi = data;
				ubx_checksum(UBX_payload_length_hi);
				UBX_step++;
		// We check if the payload lenght is valid...
		if (UBX_payload_length_hi >= UBX_MAXPAYLOAD)
				{
			if (PrintErrors)
			Serial.println("ERR:GPS_BAD_PAYLOAD_LENGTH!!");          
					UBX_step = 0;	 // Bad data, so restart to step zero and try again.		 
					ck_a = 0;
					ck_b = 0;
				}
				break;
			case 5:
				UBX_payload_length_lo = data;
				ubx_checksum(UBX_payload_length_lo);
				UBX_step++;
		UBX_payload_counter = 0;
				break;
			case 6:				 // Payload data read...
	if (UBX_payload_counter < UBX_payload_length_hi)	// We stay in this state until we reach the payload_length
				{
					UBX_buffer[UBX_payload_counter] = data;
					ubx_checksum(data);
					UBX_payload_counter++;
					if (UBX_payload_counter == UBX_payload_length_hi)
						UBX_step++;
				}
				break;
			case 7:
				UBX_ck_a = data;	 // First checksum byte
				UBX_step++;
				break;
			case 8:
				UBX_ck_b = data;	 // Second checksum byte
			 
	  // We end the GPS read...
				if((ck_a == UBX_ck_a) && (ck_b == UBX_ck_b))	 // Verify the received checksum with the generated checksum.. 
				parse_ubx_gps();							 // Parse the new GPS packet
				else
			{
			if (PrintErrors)
			Serial.println("ERR:GPS_CHK!!");
			}
        // Variable initialization
				UBX_step = 0;
				ck_a = 0;
				ck_b = 0;
				GPS_timer = millis(); // Restarting timer...
				break;
		}
		}		// End for...
  // If we don´t receive GPS packets in 2 seconds => Bad FIX state
	if ((millis() - GPS_timer) > 2000)
		{
	Fix = 0;
	if (PrintErrors)
	  Serial.println("ERR:GPS_TIMEOUT!!");
		}
}

/****************************************************************
 * 
 ****************************************************************/
// Private Methods //////////////////////////////////////////////////////////////
void GPS_UBLOX_Class::parse_ubx_gps(void)
{
	int j;
//Verifing if we are in class 1, you can change this "IF" for a "Switch" in case you want to use other UBX classes.. 
//In this case all the message im using are in class 1, to know more about classes check PAGE 60 of DataSheet.
	if(UBX_class == 0x01) 
	{
		switch(UBX_id) //Checking the UBX ID
		{
		case 0x02: // ID NAV - POSLLH 
			j = 0;
			Time = join_4_bytes(&UBX_buffer[j]); // ms Time of week
			j += 4;
			Longitude = join_4_bytes(&UBX_buffer[j]); // lon * 10000000
			j += 4;
			Lattitude = join_4_bytes(&UBX_buffer[j]); // lat * 10000000
			j += 4;
     		 //Altitude = join_4_bytes(&UBX_buffer[j]);  // elipsoid heigth mm
			j += 4;
			Altitude = (float)join_4_bytes(&UBX_buffer[j]);	// MSL heigth mm
			Altitude /= 10.;									
			
			// Rescale altitude to cm
	      	//j+=4;
    		/*
			hacc = (float)join_4_bytes(&UBX_buffer[j]) / (float)1000;
			j += 4;
			vacc = (float)join_4_bytes(&UBX_buffer[j]) / (float)1000;
			j += 4;
			*/
			NewData = 1;
			break;
		case 0x03: //ID NAV - STATUS 
      //if(UBX_buffer[4] >= 0x03)
		if((UBX_buffer[4] >= 0x03) && (UBX_buffer[5] & 0x01))				
				Fix = 1; // valid position				
			else
				Fix = 0; // invalid position
			break;

		case 0x06: //ID NAV - SOL
			if((UBX_buffer[10] >= 0x03) && (UBX_buffer[11] & 0x01))
				Fix = 1; // valid position
			else
				Fix = 0; // invalid position				
			UBX_ecefVZ = join_4_bytes(&UBX_buffer[36]);	// Vertical Speed in cm / s
			NumSats = UBX_buffer[47];										// Number of sats...		 
			break;

		case 0x12: // ID NAV - VELNED 
			j = 16;
			Speed_3d = join_4_bytes(&UBX_buffer[j]); // cm / s
			j += 4;
			Ground_Speed = join_4_bytes(&UBX_buffer[j]); // Ground speed 2D cm / s
			j += 4;
			Ground_Course = join_4_bytes(&UBX_buffer[j]); // Heading 2D deg * 100000
			Ground_Course /= 1000;	// Rescale heading to deg * 100
			j += 4;
      /*
			sacc = join_4_bytes(&UBX_buffer[j]) // Speed accuracy
			j += 4;
			headacc = join_4_bytes(&UBX_buffer[j]) // Heading accuracy
			j += 4;
			*/
			break; 
			}
		}	 
}


/****************************************************************
 * 
 ****************************************************************/
 // Join 4 bytes into a long
long GPS_UBLOX_Class::join_4_bytes(unsigned char Buffer[])
{
	union long_union {
	int32_t dword;
	uint8_t	byte[4];
} longUnion;

	longUnion.byte[0] = *Buffer;
	longUnion.byte[1] = *(Buffer + 1);
	longUnion.byte[2] = *(Buffer + 2);
	longUnion.byte[3] = *(Buffer + 3);
	return(longUnion.dword);
}

/****************************************************************
 * 
 ****************************************************************/
// Ublox checksum algorithm
void GPS_UBLOX_Class::ubx_checksum(byte ubx_data)
{
	ck_a += ubx_data;
	ck_b += ck_a; 
}

GPS_UBLOX_Class GPS;