GPStracker/soft/nmea.c

#ifdef PC_BUILD
#include "../gps-test-tool/main.h"
#else
#include "main.h"
#endif

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

uint16_t get_line (		/* 0:line incomplete or timed out, >0: Number of bytes received. */
	char *buff,
	uint16_t sz_buf
)
{
	char c;
	static uint16_t i = 0;
	uint16_t ret_len;

	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 (System.keypress) /* process user keypress */
			return 0;
		if (!uart0_test()) {
			sleep();
			continue;
		}
		c = (char)uart0_get();
		if (i == 0 && c != '$' )
			continue;	/* Find start of line */
		if (c == '\n' || c == '\r') {
			buff[i++] = '\r';
			buff[i++] = '\n';
			buff[i++] = '\0'; /* add null termination for string */
			break;	/* EOL */
		}
		buff[i++] = c;
		uart1_put(c);
		if (i >= sz_buf - 3) /* keep 3 bytes for terminating character */
			i = 0;	/* Buffer overflow (abort this line) */
	}
	ret_len = i;
	i = 0;
	if (ret_len > 0) {
		uart1_put('\r');
		uart1_put('\n');
	}
	return ret_len;
}

/* 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;

	p = gp_col(str, 7); /* satellites used */
	System.satellites_used = atoi(p);

	if (System.satellites_used >= System.conf.min_sats) {
		System.sat_count_low = 0;
	} else {
		System.sat_count_low = 1;
	}

	/* check validity */
	p = gp_col(str, 6);
	if (*p == '0') {
		System.location_valid = LOC_INVALID;
		return;
	}
	
	if (!System.sat_count_low)
		System.location_valid = LOC_VALID_NEW; /* don't accept the coordinates otherwise, even if reported valid */

	/* 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, 6); /* fix type */
	if (*p == '2')
		System.sbas = 1;
	else
		System.sbas = 0;
	
	p = gp_col(str, 9); /* MSL altitude */
	xatof(&p, &tmp);
	location.alt = tmp;

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

static void gp_vtg_parse(const char *str) {
	const char *p;
	double speed;
	
	p = gp_col(str, 9);
	if (*p == 'N') /* Not valid */
		return;
	
	p = gp_col(str, 7); /* speed in km/h */
	xatof(&p, &speed);
	System.speed = speed+0.5;
}

/*$PMTK355*31<CR><LF>
Return $PMTK001,355,3,1,0,0*2E “$PMTK001,355,3,GLON_Enable,BEIDOU_Enable,GALILEO_Enable”
The GLONASS search mode is enabled. */
static void pmtk001_parse(const char *str) {
	const char *p;

	/* check validity */
	p = gp_col(str, 1);
	if (strcmp_P(p, PSTR("355"))) /* not the PMTK355 reply */
		return;
	p = gp_col(str, 2);
	if (*p == '0' || *p == '1') { /* invalid / unsupported */
		System.gps_only = 1;
		xputs_P(PSTR("GPS only\r\n"));
	} else {
		System.gps_only = 0;
		xputs_P(PSTR("Multi GNSS\r\n"));
	}

	gps_initialize();
}

unsigned char nmea_checksum(const char *str) {
	unsigned char cs = 0;
	while (*str && *str != '*') {
		cs ^= *str++; /* NMEA checksum is quite primitive, but still should catch simple bitstream errors or truncated lines */
	}
	return cs;
}

time_t gps_parse(const char *str) {	/* Get all required data from NMEA sentences */
	signed int len = strlen(str)-2; /* remove final \r\n */
	const char *checksum;
	unsigned char calc_checksum, inc_checksum;
	signed int i;
	char c;

	if (len < 4)
		return 0; /* each message must contain $.*xx where . is one or more actual data characters and xx is the checksum */

	for (i = len-1; i && i >= (len-2); i--) { /* find checksum */
		if (str[i] == '*')
			break;
	}
	checksum = str+i+1; /* skip * character */
	inc_checksum = 0; /* parse hex string */
	while (*checksum && isalnum(*checksum)) {
		inc_checksum *= 16;
		c = *checksum++;
		if (c >= '0' && c <= '9') {
			inc_checksum += c - '0';
		} else if (c >= 'a' && c <= 'f') {
			inc_checksum += c - 'a' + 10;
		} else if (c >= 'A' && c <= 'F') {
			inc_checksum += c - 'A' + 10;
		} else {
			xputs_P(PSTR("Invalid NMEA: malformed checksum\r\n"));
			return 0; /* invalid checksum character */
		}
	}
	
	str++; /* drop initial $ */

	calc_checksum = nmea_checksum(str);
	if (inc_checksum != calc_checksum) {
		xputs_P(PSTR("Invalid NMEA checksum received\r\n"));
		return 0;
	}
	
	if (!gp_comp(str, PSTR("GPRMC")) || !gp_comp(str, PSTR("GNRMC")) || !gp_comp(str, PSTR("BDRMC")) || !gp_comp(str, PSTR("GARMC"))) {
		return gp_rmc_parse(str);
	}
	if (!gp_comp(str, PSTR("GPGGA")) || !gp_comp(str, PSTR("GNGGA")) || !gp_comp(str, PSTR("BDGGA")) || !gp_comp(str, PSTR("GAGGA"))) {
		gp_gga_parse(str);
		return 0;
	}
	if (!gp_comp(str, PSTR("GPVTG")) || !gp_comp(str, PSTR("GNVTG"))) {
		gp_vtg_parse(str);
		return 0;
	}
	if (!System.gps_initialized && !gp_comp(str, PSTR("PMTK011"))) {
		gps_initialize();
		return 0;
	}
	if (!gp_comp(str, PSTR("PMTK001"))) {
		pmtk001_parse(str);
		return 0;
	}
	return 0;
}

void uart0_put_wrap(int c) {
	uart0_put((char)c);
}

void gps_initialize(void) {
	/*
	 * PMTK355: query gnss search mode (will fail if only GPS is supported)
	 * PMTK353: set gnss search mode (GPS/Galileo/Glonass/Beidou)
	 * PMTK313: enable SBAS
	 */
	switch (System.gps_initialized) {
		case GPS_INIT_NOT_INITIALIZED:
			xfprintf(uart0_put_wrap, PSTR("$PMTK355*31\r\n"));
			xputs_P(PSTR("GNSS mode query sent\r\n"));
			System.gps_initialized = GPS_INIT_QUERY_SENT;
			break;
		case GPS_INIT_QUERY_SENT:
			if (get_flag(CONFFLAG_ENABLE_SBAS)) {
				xfprintf(uart0_put_wrap, PSTR("$PMTK313,1*2E\r\n"));
				xputs_P(PSTR("SBAS enable sent\r\n"));
			} else {
				xfprintf(uart0_put_wrap, PSTR("$PMTK313,0*2F\r\n"));
				xputs_P(PSTR("SBAS disable sent\r\n"));
			}
			if (!System.gps_only) {
				switch (System.conf.gnss_mode) {
					default:
					case GNSS_MODE_GPS_GLONASS_GALILEO:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,1,1,1,0,0*2A\r\n"));
						break;
					case GNSS_MODE_GPS:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,1,0,0,0,0*2A\r\n"));
						break;
					case GNSS_MODE_GPS_GALILEO:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,1,0,1,0,0*2B\r\n"));
						break;
					case GNSS_MODE_GALILEO:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,0,0,1,0,0*2A\r\n"));
						break;
					case GNSS_MODE_GPS_BEIDOU:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,1,0,0,0,1*2B\r\n"));
						break;
					case GNSS_MODE_BEIDOU:
						xfprintf(uart0_put_wrap, PSTR("$PMTK353,0,0,0,0,1*2A\r\n"));
						break;
				}
				xputs_P(PSTR("GNSS mode setting sent\r\n"));
			} else {
				System.conf.gnss_mode = GNSS_MODE_GPS;
			}
			break;
		default:
			break;
	}
}

void check_min_sat_limit(void) {
	if (System.conf.min_sats > 6 && (System.conf.gnss_mode == GNSS_MODE_GPS || System.conf.gnss_mode == GNSS_MODE_GALILEO || System.conf.gnss_mode == GNSS_MODE_BEIDOU)) {
		 /* by geometry, max visible number is 6..12 */
		 System.conf.min_sats = 6;
	}
}