Examples and demos

There are 2 very basic examples provided with the library.

Parse block of data

In this example, block of data is prepared as big string array and sent to processing function in single shot. Application can then check if GPS signal has been detected as valid and use other data accordingly.

Minimum example code
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/**
 * This example uses direct processing function
 * to process dummy NMEA data from GPS receiver
 */
#include "gps/gps.h"
#include <string.h>
#include <stdio.h>

/* GPS handle  */
gps_t hgps;

/**
 * \brief           Dummy data from GPS receiver
 */
const char
gps_rx_data[] = ""
"$GPRMC,183729,A,3907.356,N,12102.482,W,000.0,360.0,080301,015.5,E*6F\r\n"
"$GPRMB,A,,,,,,,,,,,,V*71\r\n"
"$GPGGA,183730,3907.356,N,12102.482,W,1,05,1.6,646.4,M,-24.1,M,,*75\r\n"
"$GPGSA,A,3,02,,,07,,09,24,26,,,,,1.6,1.6,1.0*3D\r\n"
"$GPGSV,2,1,08,02,43,088,38,04,42,145,00,05,11,291,00,07,60,043,35*71\r\n"
"$GPGSV,2,2,08,08,02,145,00,09,46,303,47,24,16,178,32,26,18,231,43*77\r\n"
"$PGRME,22.0,M,52.9,M,51.0,M*14\r\n"
"$GPGLL,3907.360,N,12102.481,W,183730,A*33\r\n"
"$PGRMZ,2062,f,3*2D\r\n"
"$PGRMM,WGS84*06\r\n"
"$GPBOD,,T,,M,,*47\r\n"
"$GPRTE,1,1,c,0*07\r\n"
"$GPRMC,183731,A,3907.482,N,12102.436,W,000.0,360.0,080301,015.5,E*67\r\n"
"$GPRMB,A,,,,,,,,,,,,V*71\r\n";

int
main() {
    /* Init GPS */
    gps_init(&hgps);

    /* Process all input data */
    gps_process(&hgps, gps_rx_data, strlen(gps_rx_data));

    /* Print messages */
    printf("Valid status: %d\r\n", hgps.is_valid);
    printf("Latitude: %f degrees\r\n", hgps.latitude);
    printf("Longitude: %f degrees\r\n", hgps.longitude);
    printf("Altitude: %f meters\r\n", hgps.altitude);

    return 0;
}

Parse received data from interrupt/DMA

Second example is a typical use case with interrupts on embedded systems. For each received character, application uses ringbuff as intermediate buffer. Data are later processed outside interrupt context.

Note

For the sake of this example, application implements interrupts as function call in while loop.

Example of buffer
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#include "stdafx.h"
#include "gps/gps.h"
#include "ringbuff/ringbuff.h"
#include <string.h>

/* GPS handle  */
gps_t hgps;

/* GPS buffer */
ringbuff_t hgps_buff;
uint8_t hgps_buff_data[12];

/**
 * \brief           Dummy data from GPS receiver
 * \note            This data are used to fake UART receive event on microcontroller
 */
const char
gps_rx_data[] = ""
"$GPRMC,183729,A,3907.356,N,12102.482,W,000.0,360.0,080301,015.5,E*6F\r\n"
"$GPRMB,A,,,,,,,,,,,,V*71\r\n"
"$GPGGA,183730,3907.356,N,12102.482,W,1,05,1.6,646.4,M,-24.1,M,,*75\r\n"
"$GPGSA,A,3,02,,,07,,09,24,26,,,,,1.6,1.6,1.0*3D\r\n"
"$GPGSV,2,1,08,02,43,088,38,04,42,145,00,05,11,291,00,07,60,043,35*71\r\n"
"$GPGSV,2,2,08,08,02,145,00,09,46,303,47,24,16,178,32,26,18,231,43*77\r\n"
"$PGRME,22.0,M,52.9,M,51.0,M*14\r\n"
"$GPGLL,3907.360,N,12102.481,W,183730,A*33\r\n"
"$PGRMZ,2062,f,3*2D\r\n"
"$PGRMM,WGS84*06\r\n"
"$GPBOD,,T,,M,,*47\r\n"
"$GPRTE,1,1,c,0*07\r\n"
"$GPRMC,183731,A,3907.482,N,12102.436,W,000.0,360.0,080301,015.5,E*67\r\n"
"$GPRMB,A,,,,,,,,,,,,V*71\r\n";
static size_t write_ptr;
static void uart_irqhandler(void);

int
main() {
    uint8_t rx;

    /* Init GPS */
    gps_init(&hgps);

    /* Create buffer for received data */
    ringbuff_init(&hgps_buff, hgps_buff_data, sizeof(hgps_buff_data));

    while (1) {
        /* Add new character to buffer */
        /* Fake UART interrupt handler on host microcontroller */
        uart_irqhandler();

        /* Process all input data */
        /* Read from buffer byte-by-byte and call processing function */
        if (gps_buff_get_full(&hgps_buff)) {    /* Check if anything in buffer now */
            while (gps_buff_read(&hgps_buff, &rx, 1) == 1) {
                gps_process(&hgps, &rx, 1);     /* Process byte-by-byte */
            }
        } else {
            /* Print all data after successful processing */
            printf("Latitude: %f degrees\r\n", hgps.latitude);
            printf("Longitude: %f degrees\r\n", hgps.longitude);
            printf("Altitude: %f meters\r\n", hgps.altitude);
            break;
        }
    }

    return 0;
}

/**
 * \brief           Interrupt handler routing for UART received character
 * \note            This is not real MCU, it is software method, called from main
 */
static void
uart_irqhandler(void) {
    /* Make interrupt handler as fast as possible */
    /* Only write to received buffer and process later */
    if (write_ptr < strlen(gps_rx_data)) {
        /* Write to buffer only */
        gps_buff_write(&hgps_buff, &gps_rx_data[write_ptr], 1);
        ++write_ptr;
    }
}