#include <avr/io.h>
#include <avr/interrupt.h>
 
#define RS 2 //RS=PD1
#define E  3 //E=PD3
 
#define TIME 10	//Time constant for LCD delay
		//Tick with 4Mhz
 
unsigned char mode=0;
 
unsigned char gga_count=0;
unsigned char vtg_count=0;
 
unsigned char gga_data[90]={};
unsigned char vtg_data[90]={};
 
void pause (unsigned int a)
{
unsigned int i;
for (i=a;i>0;i--);
}
 
void lcd_com (unsigned char lcd)//Write command to LCD
{
unsigned char temp;
temp=(lcd&~(1<<RS))|(1<<E); //RS=0 - it's command
PORTD=temp; //Write higth tetrade, RS, E to portA
asm("nop"); //Settle pause
PORTD=temp&~(1<<E); //Write higth tetrade to LCD
temp=((lcd*16)&~(1<<RS))|(1<<E); //RS=0 - it's command
PORTD=temp; //Write low tetrade, RS, E to portA
asm("nop"); //Settle pause
PORTD=temp&~(1<<E); //Write low tetrade to LCD
pause (10*TIME); //Pause for executing command
}
 
void lcd_dat (unsigned char lcd)//Write data to LCD
{
unsigned char temp;
temp=(lcd|(1<<RS))|(1<<E); //RS=1 - it's data 
PORTD=temp; //Write higth tetrade, RS, E to portA
asm("nop"); //Settle pause
PORTD=temp&~(1<<E); //Write higth tetrade to LCD
temp=((lcd*16)|(1<<RS))|(1<<E); //RS=1 - it's data
PORTD=temp; //Write low tetrade, RS, E to portA
asm("nop"); //Settle pause
PORTD=temp&~(1<<E); //Write low tetrade to LCD
pause(TIME); //Pause for loading data
}
 
void lcd_init (void)    //Init LCD
{
lcd_com(0x2c); //4-wire data bus, 1-row, 5x8 symbol size
pause(100*TIME);
lcd_com(0x0c); //Show image, cursor show
pause(1000*TIME);
lcd_com(0x01); //Clear screen and set cursor on 0x00 position
pause (100*TIME);
}
 
void uart_init(void)
{
UBRRH = 0x00; //Set 4800 bit per second
UBRRL = 0x33;
UCSRA = 0x00;
UCSRB = (1<<RXCIE)|(1<<RXEN)|(0<<TXEN);	
//Receive and transmit enable, interrupt on receive complete enabled
UCSRC = (1<<URSEL)|(1<<UCSZ1)|(1<<UCSZ0);	
}
 
unsigned char search_gga_field (unsigned char x)//Search x-th field in GGA packet
{ 
unsigned char i, c;
c=0;
for (i=0;i<gga_count;i++)
{
if (gga_data[i]==',') c++;
if (c==x) return i+1;
}
return 0;
}
 
//Search x-th field in VTG packet
unsigned char search_vtg_field (unsigned char x)
{ 
unsigned char i, c;
c=0;
for (i=0;i<vtg_count;i++)
{
if (vtg_data[i]==',') c++;
if (c==x) return i+1;
}
return 0;
}
 
void write_gps_data (unsigned char crc_valid)	//Write GPS data on LCD
{ 
unsigned char i,temp;
if (crc_valid==0) {
//If CRC not confirm
lcd_init ();
lcd_dat('n');
lcd_dat('o');
lcd_dat(' ');
lcd_dat('v');
lcd_dat('a');
lcd_dat('l');
lcd_dat('i');
lcd_dat('d');
return;
}
 
if (gga_data[search_gga_field(6)]=='0') 
{//If no GPS signal
lcd_init(); 
lcd_dat('n'); lcd_dat('o'); lcd_dat(' '); 
lcd_dat('s'); lcd_dat('i'); lcd_dat('g'); 
lcd_dat('n'); lcd_dat('a'); lcd_dat('l');
 
lcd_com(0xc0);
lcd_dat(gga_data[search_gga_field(7)+1]);
lcd_dat(' '); lcd_dat('s'); lcd_dat('a');
lcd_dat('t'); lcd_dat(' '); lcd_dat('a');
lcd_dat('v'); lcd_dat('a'); lcd_dat('i');
lcd_dat('l'); lcd_dat('a'); lcd_dat('b');
lcd_dat('l'); lcd_dat('e');
return;
}
if (mode==0) 
{//Write Latitude and Longitude
lcd_init();
lcd_dat('L'); lcd_dat('a'); lcd_dat('t');
lcd_dat(':');
temp=search_gga_field(2);
for (i=temp;i<temp+9;i++)//Write Latitude
{
if ((i-temp)==2) lcd_dat(0xdf);
lcd_dat (gga_data[i]);
}
lcd_dat(0xe7);
lcd_dat (gga_data[search_gga_field(3)]);
 
               lcd_com(0xc0);
               lcd_dat('L');
               lcd_dat('n');
               lcd_dat(':');
               temp=search_gga_field(4);
               for (i=temp;i<temp+10;i++)	//Write Longitude
                {
                 if ((i-temp)==3) lcd_dat(0xdf);
                 lcd_dat (gga_data[i]);
                }
               lcd_dat (0xe7);
               lcd_dat (gga_data[search_gga_field(5)]);
              }
 if (mode==1) {			//Write altitude and speed
               lcd_init();
			   lcd_dat('A'); lcd_dat('l'); lcd_dat('t');
			   lcd_dat('i'); lcd_dat('t'); lcd_dat('u');
			   lcd_dat('d'); lcd_dat('e'); lcd_dat(' ');
               temp=search_gga_field(9);
			   while (gga_data[temp]!=',')	//Write altitude
			    {
				 lcd_dat(gga_data[temp]);
				 temp++;
				}
			   lcd_dat('m');
 
			   lcd_com(0xc0);
			   lcd_dat('S'); lcd_dat('p');
			   lcd_dat('e'); lcd_dat('e');
			   lcd_dat('d'); lcd_dat(' ');
 
			   temp=search_vtg_field(7);
			   while (vtg_data[temp]!=',')	//Write speed
			    {
				 lcd_dat(vtg_data[temp]);
				 temp++;
				}
			   lcd_dat('k'); lcd_dat('m');
			   lcd_dat('/'); lcd_dat('h');
              } 	
 if (mode==2) {			//Write UTC time and used satellites
               lcd_init();	
			   lcd_dat('U'); lcd_dat('T');
			   lcd_dat('C'); lcd_dat(' ');
 
			   temp=search_gga_field(1);
			   for (i=temp;i<temp+6;i++)	//Write UTC
			    {
				 if (((i-temp)==2)||((i-temp)==4) ) lcd_dat (':');
				 lcd_dat(gga_data[i]);
                }
               lcd_com(0xc0);
               lcd_dat('S'); lcd_dat('a'); lcd_dat('t');
               lcd_dat('e'); lcd_dat('l'); lcd_dat('l');
               lcd_dat('i'); lcd_dat('t'); lcd_dat('e');
               lcd_dat('s'); lcd_dat(' ');
 
			   temp=search_gga_field(7);
			   lcd_dat(gga_data[temp]);	//Write satellites
			   if (gga_data[temp+1]!=',') lcd_dat(gga_data[temp+1]);
              }
 
  return; 
}
 
unsigned char check_crc (void)		//Check CRC16
{ /*unsigned char i,gga_crc,vtg_crc;
 
 gga_crc=0x00;
 
 i=1;
 while ((gga_data[i]!='*')&&(i<90))
  {
   gga_crc^=gga_data[i];
   i++;
  }
 i++;
 if (gga_data[i]!=(0x30+(gga_crc>>4))) return 0;
 i++;
 if (gga_data[i]!=(0x30+(gga_crc&0x0f))) return 0;
 
 vtg_crc=0x00;
 
 i=1;
 while ((vtg_data[i]!='*')&&(i<90))
  {
   vtg_crc^=vtg_data[i];
   i++;
  }
 i++;
 if (vtg_data[i]!=(0x30+(vtg_crc>>4))) return 0;
 i++;
 if (vtg_data[i]!=(0x30+(vtg_crc&0x0f))) return 0; */
 
 return 1;
}
 
ISR (USART_RXC_vect)	//Starts when first byte of NMEA message been received
{ 
 gga_count=0;
 gga_data[gga_count]=UDR;//Get first byte to GGA packet
 gga_count++;
 
 do {			//Receive GGA packet 
 
  while ( !(UCSRA & (1<<RXC)) )	
   ;
     gga_data[gga_count]=UDR;
	 gga_count++;
 
 } while ((gga_data[gga_count-1]!=0x0a)&&(gga_count<90));
 
 vtg_count=0;		//Receive VTG packet
 do {
 
  while ( !(UCSRA & (1<<RXC)) )
   ;
     vtg_data[vtg_count]=UDR;
	 vtg_count++;
 
 } while ((vtg_data[vtg_count-1]!=0x0a)&&(vtg_count<90));
 
 write_gps_data(check_crc());	//Write data and check CRC16
 
 return;
}
 
int main(void)
{ 
 DDRD=0xfc;		//Init PORTD as output
 
 DDRB=0x00;		//Init PORTB, PB0 as input
 PORTB=0x01;
 
 pause(5000);		//Settle pause
 lcd_init();		//Init LCD
 
 lcd_dat('n'); lcd_dat('o'); lcd_dat(' ');
 lcd_dat('g'); lcd_dat('p'); lcd_dat('s');
 lcd_dat(' '); lcd_dat('m'); lcd_dat('o');
 lcd_dat('d'); lcd_dat('u'); lcd_dat('l');
 lcd_dat('e');
 
 uart_init();		//Init UART
 sei();			//Interrupt enable
 while (1) 
  if ((PINB&0x01)==0x00) {	//If key pressed
                           while ((PINB&0x01)==0x00)	//Wait to unpress
			    ;
			   pause(1000);	 //Pause
                           mode=(mode+1)%3;	//Change mode
                         }
 
return 1;
}