GPStracker/soft/nmea.c

#include <avr/wdt.h>
#include <stddef.h>
#include <string.h>
#include <stdlib.h>
#include <avr/sleep.h>
#include "nmea.h"
#include "main.h"
#include "uart0.h"
#include "uart1.h"
#include "xprintf.h"

/*----------------------------------------------------*/
/*  Get a line received from GPS module               */
/*----------------------------------------------------*/

UINT get_line (		/* 0:Brownout or timeout, >0: Number of bytes received. */
	char *buff,
	UINT sz_buf
)
{
	char c;
	UINT i = 0;

	set_timer(recv_timeout, 1000);

	for (;;) {
		wdt_reset();
		if (FLAGS & (F_LVD | F_POWEROFF))
			return 0;	/* A brownout is detected */
		if (timer_expired(recv_timeout))
			return 0; /* timeout; continue the main loop */
		if (!uart0_test()) {
			sleep();
			continue;
		}
		c = (char)uart0_get();
		uart1_put(c);
		if (i == 0 && c != '$')
			continue;	/* Find start of line */
		buff[i++] = c;
		if (c == '\n')
			break;	/* EOL */
		if (i >= sz_buf)
			i = 0;	/* Buffer overflow (abort this line) */
	}

	return i;
}

/* Compare sentence header string */
BYTE gp_comp (const char *str1, __flash const char *str2)
{
	char c;

	do {
		c = pgm_read_byte(str2++);
	} while (c && c == *str1++);
	return c;
}

#define FIELD_BUF_LEN	32

/* Get a column item */
static
const char* gp_col (	/* Returns pointer to the item (returns a NULL when not found) */
	const char* buf,	/* Pointer to the sentence */
	BYTE col			/* Column number (0 is the 1st item) */
) {
	BYTE c;
	static char field_buf[FIELD_BUF_LEN];
	unsigned char length = 0;

	while (col) {
		do {
			c = *buf++;
			if (c <= ' ') return NULL;
		} while (c != ',');
		col--;
	}
	while (*buf && *buf != ',' && length < FIELD_BUF_LEN-1) {
		field_buf[length++] = *buf++;
	}
	field_buf[length] = '\0';
	return field_buf;
}

unsigned int gp_val(const char *db, unsigned char count) {
	unsigned int out = 0;

	while (count--) {
		unsigned char n;
		n = *db - '0';
		if (n >= 10)
			return 0;
		out *= 10;
		out += n;
		db++;
	}
	return out;
}

static time_t gp_rmc_parse(const char *str) {
	const char *p;
	struct tm tmc;

	p = gp_col(str, 1);		/* Get h:m:s */
	if (!p)
		return 0;
	tmc.tm_hour = gp_val(p, 2);
	tmc.tm_min = gp_val(p+2, 2);
	tmc.tm_sec = gp_val(p+4, 2);

	p = gp_col(str, 9);		/* Get y:m:d */
	if (!p)
		return 0;
	tmc.tm_mday = gp_val(p, 2);
	tmc.tm_mon = gp_val(p+2, 2) - 1;
	tmc.tm_year = gp_val(p+4, 2) + 100;

	utc = mktime(&tmc);				/* Check time validity */
	if (utc == -1)
		return 0;

	p = gp_col(str, 2);		/* Get status */
	if (!p || *p != 'A') {
		System.location_valid = LOC_INVALID;
		FLAGS &= ~F_GPSOK;
		return 0;			/* Return 0 even is time is valid (comes from module's internal RTC) */
	}

	FLAGS |= F_GPSOK;
	
	return utc;
}

static void gp_gga_parse(const char *str) {
	const char *p;
	double tmp;

	/* check validity */
	p = gp_col(str, 6);
	if (*p == '0') {
		System.location_valid = LOC_INVALID;
		return;
	}
	
	System.location_valid = LOC_VALID_NEW;

	/* parse location */
	p = gp_col(str, 2);		/* latitude */
	location.lat = gp_val(p, 2);	/* degrees */
	p += 2;
	xatof(&p, &tmp);	/* minutes */
	tmp /= 60;			/* convert minutes to degrees */
	location.lat += tmp;

	p = gp_col(str, 3);	/* N/S */
	if (*p != 'N')
		location.lat = -location.lat;
	
	p = gp_col(str, 4);		/* longitude */
	location.lon = gp_val(p, 3);	/* degrees */
	p += 3;
	xatof(&p, &tmp);	/* minutes */
	tmp /= 60;			/* convert minutes to degrees */
	location.lon += tmp;

	p = gp_col(str, 5); /* E/W */
	if (*p != 'E')
		location.lon = -location.lon;

	p = gp_col(str, 7); /* satellites used */
	System.satellites_used = atoi(p);
	
	p = gp_col(str, 9); /* MSL altitude */
	xatof(&p, &tmp);
	location.alt = tmp;

	location.time = utc; /* parsed from RMC */
}

time_t gps_parse(const char *str) {	/* Get all required data from NMEA sentences */
	if (!gp_comp(str, PSTR("$GPRMC"))) {
		return gp_rmc_parse(str);
	}
	if (!gp_comp(str, PSTR("$GPGGA"))) {
		gp_gga_parse(str);
		return 0;
	}
	return 0;
}