path: root/src/drivers/gps/ashtech.cpp

#include "ashtech.h"

#include <unistd.h>
#include <stdlib.h>
#include <stdio.h>
#include <poll.h>
#include <math.h>
#include <string.h>
#include <assert.h>
#include <systemlib/err.h>
#include <uORB/uORB.h>
#include <uORB/topics/vehicle_gps_position.h>
#include <uORB/topics/satellite_info.h>
#include <drivers/drv_hrt.h>

#include <fcntl.h>
#include <math.h>

ASHTECH::ASHTECH(const int &fd, struct vehicle_gps_position_s *gps_position, struct satellite_info_s *satellite_info):
	_fd(fd),
	_satellite_info(satellite_info),
	_gps_position(gps_position)
{
	decode_init();
	_decode_state = NME_DECODE_UNINIT;
	_rx_buffer_bytes = 0;
}

ASHTECH::~ASHTECH()
{
}

/*
 * All NMEA descriptions are taken from
 * http://www.trimble.com/OEM_ReceiverHelp/V4.44/en/NMEA-0183messages_MessageOverview.html
 */

int ASHTECH::handle_message(int len)
{
	char * endp;

	if (len < 7) { return 0; }

	int uiCalcComma = 0;

	for (int i = 0 ; i < len; i++) {
		if (_rx_buffer[i] == ',') { uiCalcComma++; }
	}

	char *bufptr = (char *)(_rx_buffer + 6);

	if ((memcmp(_rx_buffer + 3, "ZDA,", 3) == 0) && (uiCalcComma == 6)) {
		/*
		UTC day, month, and year, and local time zone offset
		An example of the ZDA message string is:

		$GPZDA,172809.456,12,07,1996,00,00*45

		ZDA message fields
		Field	Meaning
		0	Message ID $GPZDA
		1	UTC
		2	Day, ranging between 01 and 31
		3	Month, ranging between 01 and 12
		4	Year
		5	Local time zone offset from GMT, ranging from 00 through 13 hours
		6	Local time zone offset from GMT, ranging from 00 through 59 minutes
		7	The checksum data, always begins with *
		Fields 5 and 6 together yield the total offset. For example, if field 5 is -5 and field 6 is +15, local time is 5 hours and 15 minutes earlier than GMT.
		*/
		double ashtech_time = 0.0;
		int day = 0, month = 0, year = 0, local_time_off_hour __attribute__((unused)) = 0, local_time_off_min __attribute__((unused)) = 0;

		if (bufptr && *(++bufptr) != ',') { ashtech_time = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { day = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { month = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { year = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { local_time_off_hour = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { local_time_off_min = strtol(bufptr, &endp, 10); bufptr = endp; }


		int ashtech_hour = ashtech_time / 10000;
		int ashtech_minute = (ashtech_time - ashtech_hour * 10000) / 100;
		double ashtech_sec = ashtech_time - ashtech_hour * 10000 - ashtech_minute * 100;
		/*
		 * convert to unix timestamp
		 */
		struct tm timeinfo;
		timeinfo.tm_year = year - 1900;
		timeinfo.tm_mon = month - 1;
		timeinfo.tm_mday = day;
		timeinfo.tm_hour = ashtech_hour;
		timeinfo.tm_min = ashtech_minute;
		timeinfo.tm_sec = int(ashtech_sec);
		time_t epoch = mktime(&timeinfo);

		if (epoch > GPS_EPOCH_SECS) {
			uint64_t usecs = static_cast<uint64_t>((ashtech_sec - static_cast<uint64_t>(ashtech_sec))) * 1e6;

			// FMUv2+ boards have a hardware RTC, but GPS helps us to configure it
			// and control its drift. Since we rely on the HRT for our monotonic
			// clock, updating it from time to time is safe.

			timespec ts;
			ts.tv_sec = epoch;
			ts.tv_nsec = usecs * 1000;
			if (clock_settime(CLOCK_REALTIME, &ts)) {
				warn("failed setting clock");
			}

			_gps_position->time_utc_usec = static_cast<uint64_t>(epoch) * 1000000ULL;
			_gps_position->time_utc_usec += usecs;
		} else {
			_gps_position->time_utc_usec = 0;
		}

		_gps_position->timestamp_time = hrt_absolute_time();
	}

	else if ((memcmp(_rx_buffer + 3, "GGA,", 3) == 0) && (uiCalcComma == 14)) {
		/*
		  Time, position, and fix related data
		  An example of the GBS message string is:

		  $GPGGA,172814.0,3723.46587704,N,12202.26957864,W,2,6,1.2,18.893,M,-25.669,M,2.0,0031*4F

		  Note - The data string exceeds the ASHTECH standard length.
		  GGA message fields
		  Field   Meaning
		  0   Message ID $GPGGA
		  1   UTC of position fix
		  2   Latitude
		  3   Direction of latitude:
		  N: North
		  S: South
		  4   Longitude
		  5   Direction of longitude:
		  E: East
		  W: West
		  6   GPS Quality indicator:
		  0: Fix not valid
		  1: GPS fix
		  2: Differential GPS fix, OmniSTAR VBS
		  4: Real-Time Kinematic, fixed integers
		  5: Real-Time Kinematic, float integers, OmniSTAR XP/HP or Location RTK
		  7   Number of SVs in use, range from 00 through to 24+
		  8   HDOP
		  9   Orthometric height (MSL reference)
		  10  M: unit of measure for orthometric height is meters
		  11  Geoid separation
		  12  M: geoid separation measured in meters
		  13  Age of differential GPS data record, Type 1 or Type 9. Null field when DGPS is not used.
		  14  Reference station ID, range 0000-4095. A null field when any reference station ID is selected and no corrections are received1.
		  15
		  The checksum data, always begins with *
		  Note - If a user-defined geoid model, or an inclined
		*/
		double ashtech_time __attribute__((unused)) = 0.0, lat = 0.0, lon = 0.0, alt = 0.0;
		int num_of_sv __attribute__((unused)) = 0, fix_quality = 0;
		double hdop __attribute__((unused)) = 99.9;
		char ns = '?', ew = '?';

		if (bufptr && *(++bufptr) != ',') { ashtech_time = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { lat = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { ns = *(bufptr++); }

		if (bufptr && *(++bufptr) != ',') { lon = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { ew = *(bufptr++); }

		if (bufptr && *(++bufptr) != ',') { fix_quality = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { num_of_sv = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { hdop = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { alt = strtod(bufptr, &endp); bufptr = endp; }

		if (ns == 'S') {
			lat = -lat;
		}

		if (ew == 'W') {
			lon = -lon;
		}

		_gps_position->lat = (int(lat * 0.01) + (lat * 0.01 - int(lat * 0.01)) * 100.0 / 60.0) * 10000000;
		_gps_position->lon = (int(lon * 0.01) + (lon * 0.01 - int(lon * 0.01)) * 100.0 / 60.0) * 10000000;
		_gps_position->alt = alt * 1000;
		_rate_count_lat_lon++;

		if (fix_quality <= 0) {
			_gps_position->fix_type = 0;

		} else {
			/*
			 * in this NMEA message float integers (value 5) mode has higher value than fixed integers (value 4), whereas it provides lower quality,
			 * and since value 3 is not being used, I "moved" value 5 to 3 to add it to _gps_position->fix_type
			 */
			if (fix_quality == 5) { fix_quality = 3; }

			/*
			 * fix quality 1 means just a normal 3D fix, so I'm subtracting 1 here. This way we'll have 3 for auto, 4 for DGPS, 5 for floats, 6 for fixed.
			 */
			_gps_position->fix_type = 3 + fix_quality - 1;
		}

		_gps_position->timestamp_position = hrt_absolute_time();

		_gps_position->vel_m_s = 0;                                  /**< GPS ground speed (m/s) */
		_gps_position->vel_n_m_s = 0;                                /**< GPS ground speed in m/s */
		_gps_position->vel_e_m_s = 0;                                /**< GPS ground speed in m/s */
		_gps_position->vel_d_m_s = 0;                                /**< GPS ground speed in m/s */
		_gps_position->cog_rad =
			0;                                  /**< Course over ground (NOT heading, but direction of movement) in rad, -PI..PI */
		_gps_position->vel_ned_valid = true;                         /**< Flag to indicate if NED speed is valid */
		_gps_position->c_variance_rad = 0.1;
		_gps_position->timestamp_velocity = hrt_absolute_time();
		return 1;

	} else if ((memcmp(_rx_buffer, "$PASHR,POS,", 11) == 0) && (uiCalcComma == 18)) {
		/*
		Example $PASHR,POS,2,10,125410.00,5525.8138702,N,03833.9587380,E,131.555,1.0,0.0,0.007,-0.001,2.0,1.0,1.7,1.0,*34

		    $PASHR,POS,d1,d2,m3,m4,c5,m6,c7,f8,f9,f10,f11,f12,f13,f14,f15,f16,s17*cc
		    Parameter Description Range
		      d1 Position mode 0: standalone
		                       1: differential
		                       2: RTK float
		                       3: RTK fixed
		                       5: Dead reckoning
		                       9: SBAS (see NPT setting)
		      d2 Number of satellite used in position fix 0-99
		      m3 Current UTC time of position fix (hhmmss.ss) 000000.00-235959.99
		      m4 Latitude of position (ddmm.mmmmmm) 0-90 degrees 00-59.9999999 minutes
		      c5 Latitude sector N, S
		      m6 Longitude of position (dddmm.mmmmmm) 0-180 degrees 00-59.9999999 minutes
		      c7 Longitude sector E,W
		      f8 Altitude above ellipsoid +9999.000
		      f9 Differential age (data link age), seconds 0.0-600.0
		      f10 True track/course over ground in degrees 0.0-359.9
		      f11 Speed over ground in knots 0.0-999.9
		      f12 Vertical velocity in decimeters per second +999.9
		      f13 PDOP 0-99.9
		      f14 HDOP 0-99.9
		      f15 VDOP 0-99.9
		      f16 TDOP 0-99.9
		      s17 Reserved no data
		      *cc Checksum
		    */
		bufptr = (char *)(_rx_buffer + 10);

		/*
		 * Ashtech would return empty space as coordinate (lat, lon or alt) if it doesn't have a fix yet
		 */
		int coordinatesFound = 0;
		double ashtech_time __attribute__((unused)) = 0.0, lat = 0.0, lon = 0.0, alt = 0.0;
		int num_of_sv __attribute__((unused)) = 0, fix_quality = 0;
		double track_true = 0.0, ground_speed = 0.0 , age_of_corr __attribute__((unused)) = 0.0;
		double hdop __attribute__((unused)) = 99.9, vdop __attribute__((unused)) = 99.9,  pdop __attribute__((unused)) = 99.9, tdop __attribute__((unused)) = 99.9, vertic_vel = 0.0;
		char ns = '?', ew = '?';

		if (bufptr && *(++bufptr) != ',') { fix_quality = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { num_of_sv = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { ashtech_time = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') {
			/*
			 * if a coordinate is skipped (i.e. no fix), it either won't get into this block (two commas in a row)
			 * or strtod won't find anything and endp will point exactly where bufptr is. The same is for lon and alt.
			 */
			lat = strtod(bufptr, &endp);
			if (bufptr != endp) {coordinatesFound++;}
			bufptr = endp;
		}

		if (bufptr && *(++bufptr) != ',') { ns = *(bufptr++); }

		if (bufptr && *(++bufptr) != ',') {
			lon = strtod(bufptr, &endp);
			if (bufptr != endp) {coordinatesFound++;}
			bufptr = endp;
		}

		if (bufptr && *(++bufptr) != ',') { ew = *(bufptr++); }

		if (bufptr && *(++bufptr) != ',') {
			alt = strtod(bufptr, &endp);
			if (bufptr != endp) {coordinatesFound++;}
			bufptr = endp;
		}

		if (bufptr && *(++bufptr) != ',') { age_of_corr = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { track_true = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { ground_speed = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { vertic_vel = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { pdop = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { hdop = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { vdop = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { tdop = strtod(bufptr, &endp); bufptr = endp; }

		if (ns == 'S') {
			lat = -lat;
		}

		if (ew == 'W') {
			lon = -lon;
		}

		_gps_position->lat = (int(lat * 0.01) + (lat * 0.01 - int(lat * 0.01)) * 100.0 / 60.0) * 10000000;
		_gps_position->lon = (int(lon * 0.01) + (lon * 0.01 - int(lon * 0.01)) * 100.0 / 60.0) * 10000000;
		_gps_position->alt = alt * 1000;
		_rate_count_lat_lon++;

		if (coordinatesFound < 3) {
			_gps_position->fix_type = 0;

		} else {
			_gps_position->fix_type = 3 + fix_quality;
		}

		_gps_position->timestamp_position = hrt_absolute_time();

		double track_rad = track_true * M_PI / 180.0;

		double velocity_ms = ground_speed  / 1.9438445;			/** knots to m/s */
		double velocity_north = velocity_ms * cos(track_rad);
		double velocity_east  = velocity_ms * sin(track_rad);

		_gps_position->vel_m_s = velocity_ms;                            /**< GPS ground speed (m/s) */
		_gps_position->vel_n_m_s = velocity_north;                       /**< GPS ground speed in m/s */
		_gps_position->vel_e_m_s = velocity_east;                        /**< GPS ground speed in m/s */
		_gps_position->vel_d_m_s = -vertic_vel;                      /**< GPS ground speed in m/s */
		_gps_position->cog_rad =
			track_rad;                              /**< Course over ground (NOT heading, but direction of movement) in rad, -PI..PI */
		_gps_position->vel_ned_valid = true;                             /**< Flag to indicate if NED speed is valid */
		_gps_position->c_variance_rad = 0.1;
		_gps_position->timestamp_velocity = hrt_absolute_time();
		return 1;

	} else if ((memcmp(_rx_buffer + 3, "GST,", 3) == 0) && (uiCalcComma == 8)) {
		/*
		  Position error statistics
		  An example of the GST message string is:

		  $GPGST,172814.0,0.006,0.023,0.020,273.6,0.023,0.020,0.031*6A

		  The Talker ID ($--) will vary depending on the satellite system used for the position solution:

		  $GP - GPS only
		  $GL - GLONASS only
		  $GN - Combined
		  GST message fields
		  Field   Meaning
		  0   Message ID $GPGST
		  1   UTC of position fix
		  2   RMS value of the pseudorange residuals; includes carrier phase residuals during periods of RTK (float) and RTK (fixed) processing
		  3   Error ellipse semi-major axis 1 sigma error, in meters
		  4   Error ellipse semi-minor axis 1 sigma error, in meters
		  5   Error ellipse orientation, degrees from true north
		  6   Latitude 1 sigma error, in meters
		  7   Longitude 1 sigma error, in meters
		  8   Height 1 sigma error, in meters
		  9   The checksum data, always begins with *
		*/
		double ashtech_time __attribute__((unused)) = 0.0, lat_err = 0.0, lon_err = 0.0, alt_err = 0.0;
		double min_err __attribute__((unused)) = 0.0, maj_err __attribute__((unused)) = 0.0, deg_from_north __attribute__((unused)) = 0.0, rms_err __attribute__((unused)) = 0.0;

		if (bufptr && *(++bufptr) != ',') { ashtech_time = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { rms_err = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { maj_err = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { min_err = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { deg_from_north = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { lat_err = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { lon_err = strtod(bufptr, &endp); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { alt_err = strtod(bufptr, &endp); bufptr = endp; }

		_gps_position->eph = sqrt(lat_err * lat_err + lon_err * lon_err);
		_gps_position->epv = alt_err;

		_gps_position->s_variance_m_s = 0;
		_gps_position->timestamp_variance = hrt_absolute_time();

	} else if ((memcmp(_rx_buffer + 3, "GSV,", 3) == 0)) {
		/*
		  The GSV message string identifies the number of SVs in view, the PRN numbers, elevations, azimuths, and SNR values. An example of the GSV message string is:

		  $GPGSV,4,1,13,02,02,213,,03,-3,000,,11,00,121,,14,13,172,05*67

		  GSV message fields
		  Field   Meaning
		  0   Message ID $GPGSV
		  1   Total number of messages of this type in this cycle
		  2   Message number
		  3   Total number of SVs visible
		  4   SV PRN number
		  5   Elevation, in degrees, 90 maximum
		  6   Azimuth, degrees from True North, 000 through 359
		  7   SNR, 00 through 99 dB (null when not tracking)
		  8-11    Information about second SV, same format as fields 4 through 7
		  12-15   Information about third SV, same format as fields 4 through 7
		  16-19   Information about fourth SV, same format as fields 4 through 7
		  20  The checksum data, always begins with *
		*/
		/*
		 * currently process only gps, because do not know what
		 * Global satellite ID I should use for non GPS sats
		 */
		bool bGPS = false;

		if (memcmp(_rx_buffer, "$GP", 3) != 0) {
			return 0;

		} else {
			bGPS = true;
		}

		int all_msg_num = 0, this_msg_num = 0, tot_sv_visible = 0;
		struct gsv_sat {
			int svid;
			int elevation;
			int azimuth;
			int snr;
		} sat[4];
		memset(sat, 0, sizeof(sat));

		if (bufptr && *(++bufptr) != ',') { all_msg_num = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { this_msg_num = strtol(bufptr, &endp, 10); bufptr = endp; }

		if (bufptr && *(++bufptr) != ',') { tot_sv_visible = strtol(bufptr, &endp, 10); bufptr = endp; }

		if ((this_msg_num < 1) || (this_msg_num > all_msg_num)) {
			return 0;
		}

		if ((this_msg_num == 0) && (bGPS == true)) {
			memset(_satellite_info->svid,     0, sizeof(_satellite_info->svid));
			memset(_satellite_info->used,     0, sizeof(_satellite_info->used));
			memset(_satellite_info->snr,      0, sizeof(_satellite_info->snr));
			memset(_satellite_info->elevation, 0, sizeof(_satellite_info->elevation));
			memset(_satellite_info->azimuth,  0, sizeof(_satellite_info->azimuth));
		}

		int end = 4;

		if (this_msg_num == all_msg_num) {
			end =  tot_sv_visible - (this_msg_num - 1) * 4;
			_gps_position->satellites_used = tot_sv_visible;
			_satellite_info->count = SAT_INFO_MAX_SATELLITES;
			_satellite_info->timestamp = hrt_absolute_time();
		}

		for (int y = 0 ; y < end ; y++) {
			if (bufptr && *(++bufptr) != ',') { sat[y].svid = strtol(bufptr, &endp, 10); bufptr = endp; }

			if (bufptr && *(++bufptr) != ',') { sat[y].elevation = strtol(bufptr, &endp, 10); bufptr = endp; }

			if (bufptr && *(++bufptr) != ',') { sat[y].azimuth = strtol(bufptr, &endp, 10); bufptr = endp; }

			if (bufptr && *(++bufptr) != ',') { sat[y].snr = strtol(bufptr, &endp, 10); bufptr = endp; }

			_satellite_info->svid[y + (this_msg_num - 1) * 4]      = sat[y].svid;
			_satellite_info->used[y + (this_msg_num - 1) * 4]      = ((sat[y].snr > 0) ? true : false);
			_satellite_info->snr[y + (this_msg_num - 1) * 4]       = sat[y].snr;
			_satellite_info->elevation[y + (this_msg_num - 1) * 4] = sat[y].elevation;
			_satellite_info->azimuth[y + (this_msg_num - 1) * 4]   = sat[y].azimuth;
		}
	}

	return 0;
}


int ASHTECH::receive(unsigned timeout)
{
	{
		/* poll descriptor */
		pollfd fds[1];
		fds[0].fd = _fd;
		fds[0].events = POLLIN;

		uint8_t buf[32];

		/* timeout additional to poll */
		uint64_t time_started = hrt_absolute_time();

		int j = 0;
		ssize_t bytes_count = 0;

		while (true) {

			/* pass received bytes to the packet decoder */
			while (j < bytes_count) {
				int l = 0;

				if ((l = parse_char(buf[j])) > 0) {
					/* return to configure during configuration or to the gps driver during normal work
					 * if a packet has arrived */
					if (handle_message(l) > 0) {
						return 1;
					}
				}

				/* in case we keep trying but only get crap from GPS */
				if (time_started + timeout * 1000 * 2 < hrt_absolute_time()) {
					return -1;
				}

				j++;
			}

			/* everything is read */
			j = bytes_count = 0;

			/* then poll for new data */
			int ret = ::poll(fds, sizeof(fds) / sizeof(fds[0]), timeout * 2);

			if (ret < 0) {
				/* something went wrong when polling */
				return -1;

			} else if (ret == 0) {
				/* Timeout */
				return -1;

			} else if (ret > 0) {
				/* if we have new data from GPS, go handle it */
				if (fds[0].revents & POLLIN) {
					/*
					 * We are here because poll says there is some data, so this
					 * won't block even on a blocking device.  If more bytes are
					 * available, we'll go back to poll() again...
					 */
					bytes_count = ::read(_fd, buf, sizeof(buf));
				}
			}
		}
	}

}
#define HEXDIGIT_CHAR(d) ((char)((d) + (((d) < 0xA) ? '0' : 'A'-0xA)))

int ASHTECH::parse_char(uint8_t b)
{
	int iRet = 0;

	switch (_decode_state) {
		/* First, look for sync1 */
	case NME_DECODE_UNINIT:
		if (b == '$') {
			_decode_state = NME_DECODE_GOT_SYNC1;
			_rx_buffer_bytes = 0;
			_rx_buffer[_rx_buffer_bytes++] = b;
		}

		break;

	case NME_DECODE_GOT_SYNC1:
		if (b == '$') {
			_decode_state = NME_DECODE_GOT_SYNC1;
			_rx_buffer_bytes = 0;

		} else if (b == '*') {
			_decode_state = NME_DECODE_GOT_ASTERIKS;
		}

		if (_rx_buffer_bytes >= (sizeof(_rx_buffer) - 5)) {
			_decode_state = NME_DECODE_UNINIT;
			_rx_buffer_bytes = 0;

		} else {
			_rx_buffer[_rx_buffer_bytes++] = b;
		}

		break;

	case NME_DECODE_GOT_ASTERIKS:
		_rx_buffer[_rx_buffer_bytes++] = b;
		_decode_state = NME_DECODE_GOT_FIRST_CS_BYTE;
		break;

	case NME_DECODE_GOT_FIRST_CS_BYTE:
		_rx_buffer[_rx_buffer_bytes++] = b;
		uint8_t checksum = 0;
		uint8_t *buffer = _rx_buffer + 1;
		uint8_t *bufend = _rx_buffer + _rx_buffer_bytes - 3;

		for (; buffer < bufend; buffer++) { checksum ^= *buffer; }

		if ((HEXDIGIT_CHAR(checksum >> 4) == *(_rx_buffer + _rx_buffer_bytes - 2)) &&
		    (HEXDIGIT_CHAR(checksum & 0x0F) == *(_rx_buffer + _rx_buffer_bytes - 1))) {
			iRet = _rx_buffer_bytes;
		}

		_decode_state = NME_DECODE_UNINIT;
		_rx_buffer_bytes = 0;
		break;
	}

	return iRet;
}

void ASHTECH::decode_init(void)
{

}

/*
 * ashtech board configuration script
 */

const char comm[] = "$PASHS,POP,20\r\n"\
	      "$PASHS,NME,ZDA,B,ON,3\r\n"\
	      "$PASHS,NME,GGA,B,OFF\r\n"\
	      "$PASHS,NME,GST,B,ON,3\r\n"\
	      "$PASHS,NME,POS,B,ON,0.05\r\n"\
	      "$PASHS,NME,GSV,B,ON,3\r\n"\
	      "$PASHS,SPD,A,8\r\n"\
	      "$PASHS,SPD,B,9\r\n";

int ASHTECH::configure(unsigned &baudrate)
{
	/* try different baudrates */
	const unsigned baudrates_to_try[] = {9600, 38400, 19200, 57600, 115200};


	for (unsigned int baud_i = 0; baud_i < sizeof(baudrates_to_try) / sizeof(baudrates_to_try[0]); baud_i++) {
		baudrate = baudrates_to_try[baud_i];
		set_baudrate(_fd, baudrate);
		write(_fd, comm, sizeof(comm));
	}

	set_baudrate(_fd, 115200);
	return 0;
}