gps_test.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <stdint.h>
#include <math.h>
#include "pico/stdlib.h"
#include "hardware/gpio.h"
#include "hardware/uart.h"


#define BAUD_RATE 9600
#define DATA_BITS 8
#define STOP_BITS 1
#define PARITY UART_PARITY_NONE
#define UART_TX_PIN 0
#define UART_RX_PIN 1

typedef struct GPS
{
	long Time;							// Time as read from GPS, as an integer but 12:13:14 is 121314
	long SecondsInDay;					// Time in seconds since midnight.
	int Hours, Minutes, Seconds;
	int32_t Longitude, Latitude;
	long Altitude;
	unsigned int Satellites;
	unsigned int FixQuality;
	float HDOP;
	float GeoidSeparation;
	
} GPS;

int32_t str_to_int(char *str, int len)
{
	int32_t result = 0;
	int i;
	int unit = 0;
	for (i=len - 1; i >= 0; i--)
	{	
		if(str[i] != '.'){
			int digit = str[i] - '0';
			//printf("***%d", digit);
			result = result + (digit * pow(10, unit));
			unit++;

		}	
	}

	return result;
}

void send_message(unsigned char *message, int len)
{
	int i;
	
	for (i=0; i<len; i++)
	{
		printf("%c", message[i]);

		uart_putc(uart0, message[i]);
	}
}

void setup_gps(){
	// Set up UART
	uart_init(uart0, BAUD_RATE);
	gpio_set_function(UART_TX_PIN, GPIO_FUNC_UART);
	gpio_set_function(UART_RX_PIN, GPIO_FUNC_UART);
	uart_set_format(uart0, DATA_BITS, STOP_BITS, PARITY);
}

void reset_gps(){
	// Reset GPS
	unsigned char message[] = {'$','P','M','T','K','1','0','4','*','3','7','\r','\n'};

	int length = sizeof(message)/sizeof(message[0]);

	send_message(message, length);
	
}

void processNMEA( unsigned char *Line, GPS *gps, int length){

	if(Line[0] == '$' && Line[1] == 'G' && Line[2] == 'P' && Line[3] == 'G' && Line[4] == 'G' && Line[5] == 'A'){

		printf("GGA Message Received %s", Line);

		// using strtok to split the string
		char *token = strtok(Line, ",");
		int index = 0;
		while (token != NULL) {
			printf("%d: %s \n", index, token);
			token = strtok(NULL, ",");
			index++;

			if(index == 1){
				gps->Time = atoi(token);
				gps->Hours = gps->Time / 10000;
				gps->Minutes = (gps->Time - (gps->Hours * 10000)) / 100;
				gps->Seconds = (gps->Time - (gps->Hours * 10000) - (gps->Minutes * 100));
				gps->SecondsInDay = (gps->Hours * 3600) + (gps->Minutes * 60) + gps->Seconds;
				printf("Time: %d:%d:%d \n", gps->Hours, gps->Minutes, gps->Seconds);
			}

			if(index == 2){
				int length = strlen(token);
				//printf("Length: %d \n", length);
				//printf("Latitude: %s \n", token);
				int32_t result = str_to_int(token, length);
				gps->Latitude = result;
				//printf("Result: %d \n", result);
			}

			if(index == 2 && *token == '0'){
				gps->FixQuality = 0;
				printf("No Fix \n");
			}

			if(index == 3){
				if(token[0] == 'S'){
					gps->Latitude = -gps->Latitude;
				}
			}

			if(index == 4){
				int length = strlen(token);
				int32_t result = str_to_int(token, length);
				gps->Longitude = result;
			}

			if(index == 5){
				if(token[0] == 'W'){
					gps->Longitude = -gps->Longitude;
				}
			}

			if(index == 6){
				//printf("Fix: %s \n", token);
				gps->FixQuality = atoi(token);
			}

			if(index == 7){
				gps->Satellites = atoi(token);
			}

			if(index == 8){
				//printf("HDOP: %s \n", token);
				gps->HDOP = atof(token);
			}

			if(index == 9){
				gps->Altitude = atof(token);
			}

			if(index == 10){
				//printf("Altitude Units: %s \n", token);
			}

			if(index == 11){
				//printf("Geoid Separation: %s \n", token);
				gps->GeoidSeparation = atof(token);
			}

			if(index == 12){
				//printf("Geoid Separation Units: %s \n", token);
			}

			if (gps->FixQuality == 2)
				{
				
				if(index == 13){
					//printf("Age of Differential GPS Data: %s \n", token);
				}

				if(index == 14){
					//printf("Differential Reference Station ID: %s \n", token);
				}

				if(index == 15){
					//printf("Checksum: %s \n", token);
				}
			}
			else{
				if(index == 13){
					//printf("Checksum: %s \n", token);
				}
			}

		}
	}
	
}

void readGPSData(GPS *gps){

	static unsigned char Line[100];
	static int index=0;

	if (uart_is_readable(uart0)) {
		char c = uart_getc(uart0);
		// printf("%c", c);

		if(c == '$'){

			index = 0;
			Line[index] = c;
			index++;	

		}
		else if(index > 90){

			index = 0;

		}
		else if(index > 0 && c != '\r'){
			
			Line[index] = c;
			index++;

			if(c == '\n'){

				Line[index] = '\0';
				//printf("%s", Line);
				processNMEA(Line , gps, index);
				//printf("Time: %d \n", gps.Time);
				index = 0;

			}

		}

	}

}


int main() {

	stdio_init_all();
	
	setup_gps();

	reset_gps();
 
	GPS gps;

	static unsigned char Line[100];
	static int index=0;

	while (1) {

		readGPSData(&gps);

	}
	
}