MTK MT33xx型GPS的NMEA协议解析实例

1）解析实现

gps_main.c

#include <nmea/nmea.h>
#include <string.h>
#include <stdio.h>
#include <stdint.h>
#include <stdlib.h>

#include "nrf_gpio.h"
#include "gps_main.h"
#include "main.h"

#define GPS_PIN   27

static struct gps_t
{
    char buf[100];
    uint8_t index;
    enum gps_state_t
    {
        GPS_NULL,
        START,
        PAYLOAD,
        END,
    } gps_state;
} gps;

void gps_on(void)
{
    nrf_gpio_cfg_output(GPS_PIN);
    nrf_gpio_pin_set(GPS_PIN);
    memset(gps.buf,0,sizeof(char)*100);
    gps.gps_state = START;
    gps.index = 0;
}

void gps_off(void)
{
    nrf_gpio_pin_clear(GPS_PIN);
}

void gps_buf_fill_data(uint8_t cr)
{
    switch (gps.gps_state)
    {
    case START:
        if(cr == '$')
        {
            gps.buf[gps.index++] = cr;
            gps.gps_state = PAYLOAD;
        }
        else gps.gps_state = START;
        break;

    case PAYLOAD:
        if(cr == '
')
        {
            gps.gps_state = END;
        }
        gps.buf[gps.index++] = cr;
        break;

    case END:
        if(cr == '
')
        {
            if( xSemaphoreGive( gpsSemaphore ) != pdTRUE )
            {
            }
            gps.buf[gps.index] = cr;
        }
        break;

    default:
        break;
    }
}

void gps_thread(void * arg)
{
    nmeaINFO info;
    nmeaPARSER parser;

    int size_nmeaINFO  = sizeof(nmeaINFO);
    int size_nmeaPARSER  = sizeof(nmeaPARSER);

    nmea_zero_INFO(&info);
    nmea_parser_init(&parser);

    static uint8_t gps_nmea_scanning = 0;
    static int inuse_value = 0;
    static int inview_value = 0;

    gps_on();

    for (;;)
    {
        if( xSemaphoreTake( gpsSemaphore, ( TickType_t ) 0 ) )
        {
            switch (gps_nmea_scanning)
            {
            case 0:
                if(strstr(gps.buf,"$GPRMC")!=NULL)
                {
                    if ((nmea_parse(&parser, (char*)gps.buf, (int)strlen((char*)gps.buf), &info)) > 0 )
                    {
                        printf("inuse     %d
",inuse_value);
                        printf("inview    %d
",inview_value);
                        printf("sig       %d
",info.sig);
                        printf("fix       %d
",info.fix);
                        printf("year      %d
",info.utc.year);
                        printf("mon       %d
",info.utc.mon);
                        printf("day       %d
",info.utc.day);
                        printf("hour      %d
",info.utc.hour);
                        printf("min       %d
",info.utc.min);
                        printf("sec       %d
",info.utc.sec);
                        printf("lon       %.5f
",info.lon);
                        printf("lat       %.5f
",info.lat);
                        printf("speed     %.2f
",info.speed);
                    }
                    gps_nmea_scanning = 1;
                }
                break;

            case 1:
                if(strstr(gps.buf,"$GPGGA")!=NULL)
                {
                    /*
                      MTK的GPS模组GPGGA协议内容是14项，nmealib库是解析的12项，这里手动解算inuse
                      if ((nmea_parse(&parser, (char*)gps.buf, (int)strlen((char*)gps.buf), &info)) > 0 )
                    */
                    char inuse_buf[3];
                    int count = 0, index = 0;
                    for (index = 0; index < strlen(gps.buf); ++index)
                    {
                        if (gps.buf[index] == ',')
                            ++count;
                        if (count == 7)
                            break;
                    }
                    strncpy(inuse_buf, &gps.buf[index+1], 2);
                    int n = atoi(inuse_buf);
                    inuse_value = n;
                    gps_nmea_scanning = 2;
                }
                break;

            case 2:
                if(strstr(gps.buf,"$GPGSV")!=NULL)
                {
                    if ((nmea_parse(&parser, (char*)gps.buf, (int)strlen((char*)gps.buf), &info)) > 0 )
                    {
                        inview_value =  info.satinfo.inview;
                    }
                    gps_nmea_scanning = 0;
                }
                break;

            default:
                break;
            }

            memset(gps.buf,0,sizeof(char)*100);
            gps.index = 0;
            gps.gps_state = START;
        }
    }
}

gps_main.h

#ifndef GPS_MAIN_H__
#define GPS_MAIN_H__

#include <stdint.h>

void gps_on(void);
void gps_off(void);
void gps_buf_fill_data(uint8_t cr);

void gps_thread(void * arg);

#endif

2）在串口接收函数中填充GPS缓存即可

gps_buf_fill_data(cr);

3）附件demo打包下载http://files.cnblogs.com/files/dong1/gps.rar

end