xref: /hardware/qcom/gps/loc_api/libloc_api_50001/loc_eng_nmea.cpp

/* Copyright (c) 2012, The Linux Foundation. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions are
 * met:
 *     * Redistributions of source code must retain the above copyright
 *       notice, this list of conditions and the following disclaimer.
 *     * Redistributions in binary form must reproduce the above
 *       copyright notice, this list of conditions and the following
 *       disclaimer in the documentation and/or other materials provided
 *       with the distribution.
 *     * Neither the name of The Linux Foundation nor the names of its
 *       contributors may be used to endorse or promote products derived
 *       from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESS OR IMPLIED
 * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
 * MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NON-INFRINGEMENT
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS
 * BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
 * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
 * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR
 * BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY,
 * WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE
 * OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN
 * IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 *
 */

#define LOG_NDDEBUG 0
#define LOG_TAG "LocSvc_eng_nmea"
#define GPS_PRN_START 1
#define GPS_PRN_END   32
#define GLONASS_PRN_START 65
#define GLONASS_PRN_END   96
#include <loc_eng.h>
#include <loc_eng_nmea.h>
#include <math.h>
#include "log_util.h"

/*===========================================================================
FUNCTION    loc_eng_nmea_send

DESCRIPTION
   send out NMEA sentence

DEPENDENCIES
   NONE

RETURN VALUE
   Total length of the nmea sentence

SIDE EFFECTS
   N/A

===========================================================================*/
void loc_eng_nmea_send(char *pNmea, int length, loc_eng_data_s_type *loc_eng_data_p)
{
    struct timeval tv;
    gettimeofday(&tv, (struct timezone *) NULL);
    int64_t now = tv.tv_sec * 1000LL + tv.tv_usec / 1000;
    CALLBACK_LOG_CALLFLOW("nmea_cb", %p, pNmea);
    if (loc_eng_data_p->nmea_cb != NULL)
        loc_eng_data_p->nmea_cb(now, pNmea, length);
    LOC_LOGD("NMEA <%s", pNmea);
}

/*===========================================================================
FUNCTION    loc_eng_nmea_put_checksum

DESCRIPTION
   Generate NMEA sentences generated based on position report

DEPENDENCIES
   NONE

RETURN VALUE
   Total length of the nmea sentence

SIDE EFFECTS
   N/A

===========================================================================*/
int loc_eng_nmea_put_checksum(char *pNmea, int maxSize)
{
    uint8_t checksum = 0;
    int length = 0;

    pNmea++; //skip the $
    while (*pNmea != '\0')
    {
        checksum ^= *pNmea++;
        length++;
    }

    int checksumLength = snprintf(pNmea,(maxSize-length-1),"*%02X\r\n", checksum);
    return (length + checksumLength);
}

/*===========================================================================
FUNCTION    loc_eng_nmea_generate_pos

DESCRIPTION
   Generate NMEA sentences generated based on position report

DEPENDENCIES
   NONE

RETURN VALUE
   0

SIDE EFFECTS
   N/A

===========================================================================*/
void loc_eng_nmea_generate_pos(loc_eng_data_s_type *loc_eng_data_p,
                               const UlpLocation &location,
                               const GpsLocationExtended &locationExtended,
                               unsigned char generate_nmea)
{
    ENTRY_LOG();
    time_t utcTime(location.gpsLocation.timestamp/1000);
    tm * pTm = gmtime(&utcTime);
    if (NULL == pTm) {
        LOC_LOGE("gmtime failed");
        return;
    }

    char sentence[NMEA_SENTENCE_MAX_LENGTH] = {0};
    char* pMarker = sentence;
    int lengthRemaining = sizeof(sentence);
    int length = 0;
    int utcYear = pTm->tm_year % 100; // 2 digit year
    int utcMonth = pTm->tm_mon + 1; // tm_mon starts at zero
    int utcDay = pTm->tm_mday;
    int utcHours = pTm->tm_hour;
    int utcMinutes = pTm->tm_min;
    int utcSeconds = pTm->tm_sec;

    if (generate_nmea) {
        // ------------------
        // ------$GPGSA------
        // ------------------

        uint32_t svUsedCount = 0;
        uint32_t svUsedList[32] = {0};
        uint32_t mask = loc_eng_data_p->sv_used_mask;
        for (uint8_t i = 1; mask > 0 && svUsedCount < 32; i++)
        {
            if (mask & 1)
                svUsedList[svUsedCount++] = i;
            mask = mask >> 1;
        }
        // clear the cache so they can't be used again
        loc_eng_data_p->sv_used_mask = 0;

        char fixType;
        if (svUsedCount == 0)
            fixType = '1'; // no fix
        else if (svUsedCount <= 3)
            fixType = '2'; // 2D fix
        else
            fixType = '3'; // 3D fix

        length = snprintf(pMarker, lengthRemaining, "$GPGSA,A,%c,", fixType);

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        for (uint8_t i = 0; i < 12; i++) // only the first 12 sv go in sentence
        {
            if (i < svUsedCount)
                length = snprintf(pMarker, lengthRemaining, "%02d,", svUsedList[i]);
            else
                length = snprintf(pMarker, lengthRemaining, ",");

            if (length < 0 || length >= lengthRemaining)
            {
                LOC_LOGE("NMEA Error in string formatting");
                return;
            }
            pMarker += length;
            lengthRemaining -= length;
        }

        if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_DOP)
        {   // dop is in locationExtended, (QMI)
            length = snprintf(pMarker, lengthRemaining, "%.1f,%.1f,%.1f",
                              locationExtended.pdop,
                              locationExtended.hdop,
                              locationExtended.vdop);
        }
        else if (loc_eng_data_p->pdop > 0 && loc_eng_data_p->hdop > 0 && loc_eng_data_p->vdop > 0)
        {   // dop was cached from sv report (RPC)
            length = snprintf(pMarker, lengthRemaining, "%.1f,%.1f,%.1f",
                              loc_eng_data_p->pdop,
                              loc_eng_data_p->hdop,
                              loc_eng_data_p->vdop);
        }
        else
        {   // no dop
            length = snprintf(pMarker, lengthRemaining, ",,");
        }

        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        // ------------------
        // ------$GPVTG------
        // ------------------

        pMarker = sentence;
        lengthRemaining = sizeof(sentence);

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_BEARING)
        {
            float magTrack = location.gpsLocation.bearing;
            if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_MAG_DEV)
            {
                float magTrack = location.gpsLocation.bearing - locationExtended.magneticDeviation;
                if (magTrack < 0.0)
                    magTrack += 360.0;
                else if (magTrack > 360.0)
                    magTrack -= 360.0;
            }

            length = snprintf(pMarker, lengthRemaining, "$GPVTG,%.1lf,T,%.1lf,M,", location.gpsLocation.bearing, magTrack);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining, "$GPVTG,,T,,M,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_SPEED)
        {
            float speedKnots = location.gpsLocation.speed * (3600.0/1852.0);
            float speedKmPerHour = location.gpsLocation.speed * 3.6;

            length = snprintf(pMarker, lengthRemaining, "%.1lf,N,%.1lf,K,", speedKnots, speedKmPerHour);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining, ",N,,K,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (!(location.gpsLocation.flags & GPS_LOCATION_HAS_LAT_LONG))
            length = snprintf(pMarker, lengthRemaining, "%c", 'N'); // N means no fix
        else if (LOC_POSITION_MODE_STANDALONE == loc_eng_data_p->adapter->getPositionMode().mode)
            length = snprintf(pMarker, lengthRemaining, "%c", 'A'); // A means autonomous
        else
            length = snprintf(pMarker, lengthRemaining, "%c", 'D'); // D means differential

        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        // ------------------
        // ------$GPRMC------
        // ------------------

        pMarker = sentence;
        lengthRemaining = sizeof(sentence);

        length = snprintf(pMarker, lengthRemaining, "$GPRMC,%02d%02d%02d,A," ,
                          utcHours, utcMinutes, utcSeconds);

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_LAT_LONG)
        {
            double latitude = location.gpsLocation.latitude;
            double longitude = location.gpsLocation.longitude;
            char latHemisphere;
            char lonHemisphere;
            double latMinutes;
            double lonMinutes;

            if (latitude > 0)
            {
                latHemisphere = 'N';
            }
            else
            {
                latHemisphere = 'S';
                latitude *= -1.0;
            }

            if (longitude < 0)
            {
                lonHemisphere = 'W';
                longitude *= -1.0;
            }
            else
            {
                lonHemisphere = 'E';
            }

            latMinutes = fmod(latitude * 60.0 , 60.0);
            lonMinutes = fmod(longitude * 60.0 , 60.0);

            length = snprintf(pMarker, lengthRemaining, "%02d%09.6lf,%c,%03d%09.6lf,%c,",
                              (uint8_t)floor(latitude), latMinutes, latHemisphere,
                              (uint8_t)floor(longitude),lonMinutes, lonHemisphere);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining,",,,,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_SPEED)
        {
            float speedKnots = location.gpsLocation.speed * (3600.0/1852.0);
            length = snprintf(pMarker, lengthRemaining, "%.1lf,", speedKnots);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining, ",");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_BEARING)
        {
            length = snprintf(pMarker, lengthRemaining, "%.1lf,", location.gpsLocation.bearing);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining, ",");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        length = snprintf(pMarker, lengthRemaining, "%2.2d%2.2d%2.2d,",
                          utcDay, utcMonth, utcYear);

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_MAG_DEV)
        {
            float magneticVariation = locationExtended.magneticDeviation;
            char direction;
            if (magneticVariation < 0.0)
            {
                direction = 'W';
                magneticVariation *= -1.0;
            }
            else
            {
                direction = 'E';
            }

            length = snprintf(pMarker, lengthRemaining, "%.1lf,%c,",
                              magneticVariation, direction);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining, ",,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (!(location.gpsLocation.flags & GPS_LOCATION_HAS_LAT_LONG))
            length = snprintf(pMarker, lengthRemaining, "%c", 'N'); // N means no fix
        else if (LOC_POSITION_MODE_STANDALONE == loc_eng_data_p->adapter->getPositionMode().mode)
            length = snprintf(pMarker, lengthRemaining, "%c", 'A'); // A means autonomous
        else
            length = snprintf(pMarker, lengthRemaining, "%c", 'D'); // D means differential

        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        // ------------------
        // ------$GPGGA------
        // ------------------

        pMarker = sentence;
        lengthRemaining = sizeof(sentence);

        length = snprintf(pMarker, lengthRemaining, "$GPGGA,%02d%02d%02d," ,
                          utcHours, utcMinutes, utcSeconds);

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (location.gpsLocation.flags & GPS_LOCATION_HAS_LAT_LONG)
        {
            double latitude = location.gpsLocation.latitude;
            double longitude = location.gpsLocation.longitude;
            char latHemisphere;
            char lonHemisphere;
            double latMinutes;
            double lonMinutes;

            if (latitude > 0)
            {
                latHemisphere = 'N';
            }
            else
            {
                latHemisphere = 'S';
                latitude *= -1.0;
            }

            if (longitude < 0)
            {
                lonHemisphere = 'W';
                longitude *= -1.0;
            }
            else
            {
                lonHemisphere = 'E';
            }

            latMinutes = fmod(latitude * 60.0 , 60.0);
            lonMinutes = fmod(longitude * 60.0 , 60.0);

            length = snprintf(pMarker, lengthRemaining, "%02d%09.6lf,%c,%03d%09.6lf,%c,",
                              (uint8_t)floor(latitude), latMinutes, latHemisphere,
                              (uint8_t)floor(longitude),lonMinutes, lonHemisphere);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining,",,,,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        char gpsQuality;
        if (!(location.gpsLocation.flags & GPS_LOCATION_HAS_LAT_LONG))
            gpsQuality = '0'; // 0 means no fix
        else if (LOC_POSITION_MODE_STANDALONE == loc_eng_data_p->adapter->getPositionMode().mode)
            gpsQuality = '1'; // 1 means GPS fix
        else
            gpsQuality = '2'; // 2 means DGPS fix

        if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_DOP)
        {   // dop is in locationExtended, (QMI)
            length = snprintf(pMarker, lengthRemaining, "%c,%02d,%.1f,",
                              gpsQuality, svUsedCount, locationExtended.hdop);
        }
        else if (loc_eng_data_p->pdop > 0 && loc_eng_data_p->hdop > 0 && loc_eng_data_p->vdop > 0)
        {   // dop was cached from sv report (RPC)
            length = snprintf(pMarker, lengthRemaining, "%c,%02d,%.1f,",
                              gpsQuality, svUsedCount, loc_eng_data_p->hdop);
        }
        else
        {   // no hdop
            length = snprintf(pMarker, lengthRemaining, "%c,%02d,,",
                              gpsQuality, svUsedCount);
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_ALTITUDE_MEAN_SEA_LEVEL)
        {
            length = snprintf(pMarker, lengthRemaining, "%.1lf,M,",
                              locationExtended.altitudeMeanSeaLevel);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining,",,");
        }

        if (length < 0 || length >= lengthRemaining)
        {
            LOC_LOGE("NMEA Error in string formatting");
            return;
        }
        pMarker += length;
        lengthRemaining -= length;

        if ((location.gpsLocation.flags & GPS_LOCATION_HAS_ALTITUDE) &&
            (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_ALTITUDE_MEAN_SEA_LEVEL))
        {
            length = snprintf(pMarker, lengthRemaining, "%.1lf,M,,",
                              location.gpsLocation.altitude - locationExtended.altitudeMeanSeaLevel);
        }
        else
        {
            length = snprintf(pMarker, lengthRemaining,",,,");
        }

        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

    }
    //Send blank NMEA reports for non-final fixes
    else {
        strlcpy(sentence, "$GPGSA,A,1,,,,,,,,,,,,,,,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPVTG,,T,,M,,N,,K,N", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPRMC,,V,,,,,,,,,,N", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPGGA,,,,,,0,,,,,,,,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);
    }
    // clear the dop cache so they can't be used again
    loc_eng_data_p->pdop = 0;
    loc_eng_data_p->hdop = 0;
    loc_eng_data_p->vdop = 0;

    EXIT_LOG(%d, 0);
}



/*===========================================================================
FUNCTION    loc_eng_nmea_generate_sv

DESCRIPTION
   Generate NMEA sentences generated based on sv report

DEPENDENCIES
   NONE

RETURN VALUE
   0

SIDE EFFECTS
   N/A

===========================================================================*/
void loc_eng_nmea_generate_sv(loc_eng_data_s_type *loc_eng_data_p,
                              const GpsSvStatus &svStatus, const GpsLocationExtended &locationExtended)
{
    ENTRY_LOG();

    char sentence[NMEA_SENTENCE_MAX_LENGTH] = {0};
    char* pMarker = sentence;
    int lengthRemaining = sizeof(sentence);
    int length = 0;
    int svCount = svStatus.num_svs;
    int sentenceCount = 0;
    int sentenceNumber = 1;
    int svNumber = 1;
    int gpsCount = 0;
    int glnCount = 0;

    //Count GPS SVs for saparating GPS from GLONASS and throw others

    for(svNumber=1; svNumber <= svCount; svNumber++) {
        if( (svStatus.sv_list[svNumber-1].prn >= GPS_PRN_START)&&
            (svStatus.sv_list[svNumber-1].prn <= GPS_PRN_END) )
        {
            gpsCount++;
        }
        else if( (svStatus.sv_list[svNumber-1].prn >= GLONASS_PRN_START) &&
                 (svStatus.sv_list[svNumber-1].prn <= GLONASS_PRN_END) )
        {
            glnCount++;
        }
    }

    // ------------------
    // ------$GPGSV------
    // ------------------

    if (gpsCount <= 0)
    {
        // no svs in view, so just send a blank $GPGSV sentence
        strlcpy(sentence, "$GPGSV,1,1,0,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);
    }
    else
    {
        svNumber = 1;
        sentenceNumber = 1;
        sentenceCount = gpsCount/4 + (gpsCount % 4 != 0);

        while (sentenceNumber <= sentenceCount)
        {
            pMarker = sentence;
            lengthRemaining = sizeof(sentence);

            length = snprintf(pMarker, lengthRemaining, "$GPGSV,%d,%d,%02d",
                          sentenceCount, sentenceNumber, gpsCount);

            if (length < 0 || length >= lengthRemaining)
            {
                LOC_LOGE("NMEA Error in string formatting");
                return;
            }
            pMarker += length;
            lengthRemaining -= length;

            for (int i=0; (svNumber <= svCount) && (i < 4);  svNumber++)
            {
                if( (svStatus.sv_list[svNumber-1].prn >= GPS_PRN_START) &&
                    (svStatus.sv_list[svNumber-1].prn <= GPS_PRN_END) )
                {
                    length = snprintf(pMarker, lengthRemaining,",%02d,%02d,%03d,",
                                  svStatus.sv_list[svNumber-1].prn,
                                  (int)(0.5 + svStatus.sv_list[svNumber-1].elevation), //float to int
                                  (int)(0.5 + svStatus.sv_list[svNumber-1].azimuth)); //float to int

                    if (length < 0 || length >= lengthRemaining)
                    {
                        LOC_LOGE("NMEA Error in string formatting");
                        return;
                    }
                    pMarker += length;
                    lengthRemaining -= length;

                    if (svStatus.sv_list[svNumber-1].snr > 0)
                    {
                        length = snprintf(pMarker, lengthRemaining,"%02d",
                                         (int)(0.5 + svStatus.sv_list[svNumber-1].snr)); //float to int

                        if (length < 0 || length >= lengthRemaining)
                        {
                            LOC_LOGE("NMEA Error in string formatting");
                            return;
                        }
                        pMarker += length;
                        lengthRemaining -= length;
                    }

                    i++;
               }

            }

            length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
            loc_eng_nmea_send(sentence, length, loc_eng_data_p);
            sentenceNumber++;

        }  //while

    } //if

    // ------------------
    // ------$GLGSV------
    // ------------------

    if (glnCount <= 0)
    {
        // no svs in view, so just send a blank $GLGSV sentence
        strlcpy(sentence, "$GLGSV,1,1,0,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);
    }
    else
    {
        svNumber = 1;
        sentenceNumber = 1;
        sentenceCount = glnCount/4 + (glnCount % 4 != 0);

        while (sentenceNumber <= sentenceCount)
        {
            pMarker = sentence;
            lengthRemaining = sizeof(sentence);

            length = snprintf(pMarker, lengthRemaining, "$GLGSV,%d,%d,%02d",
                          sentenceCount, sentenceNumber, glnCount);

            if (length < 0 || length >= lengthRemaining)
            {
                LOC_LOGE("NMEA Error in string formatting");
                return;
            }
            pMarker += length;
            lengthRemaining -= length;

            for (int i=0; (svNumber <= svCount) && (i < 4);  svNumber++)
            {
                if( (svStatus.sv_list[svNumber-1].prn >= GLONASS_PRN_START) &&
                    (svStatus.sv_list[svNumber-1].prn <= GLONASS_PRN_END) )      {

                    length = snprintf(pMarker, lengthRemaining,",%02d,%02d,%03d,",
                                  svStatus.sv_list[svNumber-1].prn,
                                  (int)(0.5 + svStatus.sv_list[svNumber-1].elevation), //float to int
                                  (int)(0.5 + svStatus.sv_list[svNumber-1].azimuth)); //float to int

                    if (length < 0 || length >= lengthRemaining)
                    {
                        LOC_LOGE("NMEA Error in string formatting");
                        return;
                    }
                    pMarker += length;
                    lengthRemaining -= length;

                    if (svStatus.sv_list[svNumber-1].snr > 0)
                    {
                        length = snprintf(pMarker, lengthRemaining,"%02d",
                                         (int)(0.5 + svStatus.sv_list[svNumber-1].snr)); //float to int

                        if (length < 0 || length >= lengthRemaining)
                        {
                            LOC_LOGE("NMEA Error in string formatting");
                            return;
                        }
                        pMarker += length;
                        lengthRemaining -= length;
                    }

                    i++;
               }

            }

            length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
            loc_eng_nmea_send(sentence, length, loc_eng_data_p);
            sentenceNumber++;

        }  //while

    }//if

    if (svStatus.used_in_fix_mask == 0)
    {   // No sv used, so there will be no position report, so send
        // blank NMEA sentences
        strlcpy(sentence, "$GPGSA,A,1,,,,,,,,,,,,,,,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPVTG,,T,,M,,N,,K,N", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPRMC,,V,,,,,,,,,,N", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);

        strlcpy(sentence, "$GPGGA,,,,,,0,,,,,,,,", sizeof(sentence));
        length = loc_eng_nmea_put_checksum(sentence, sizeof(sentence));
        loc_eng_nmea_send(sentence, length, loc_eng_data_p);
    }
    else
    {   // cache the used in fix mask, as it will be needed to send $GPGSA
        // during the position report
        loc_eng_data_p->sv_used_mask = svStatus.used_in_fix_mask;

        // For RPC, the DOP are sent during sv report, so cache them
        // now to be sent during position report.
        // For QMI, the DOP will be in position report.
        if (locationExtended.flags & GPS_LOCATION_EXTENDED_HAS_DOP)
        {
            loc_eng_data_p->pdop = locationExtended.pdop;
            loc_eng_data_p->hdop = locationExtended.hdop;
            loc_eng_data_p->vdop = locationExtended.vdop;
        }
        else
        {
            loc_eng_data_p->pdop = 0;
            loc_eng_data_p->hdop = 0;
            loc_eng_data_p->vdop = 0;
        }

    }

    EXIT_LOG(%d, 0);
}