LibrePilot/flight/modules/GPS/UBX.c

/**
 ******************************************************************************
 * @addtogroup OpenPilotModules OpenPilot Modules
 * @{
 * @addtogroup GPSModule GPS Module
 * @brief Process GPS information (UBX binary format)
 * @{
 *
 * @file       UBX.c
 * @author     The LibrePilot Project, http://www.librepilot.org Copyright (C) 2015-2016.
 *             The OpenPilot Team, http://www.openpilot.org Copyright (C) 2012.
 * @brief      GPS module, handles GPS and UBX stream
 * @see        The GNU Public License (GPL) Version 3
 *
 *****************************************************************************/
/*
 * This program is free software; you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation; either version 3 of the License, or
 * (at your option) any later version.
 *
 * This program is distributed in the hope that it will be useful, but
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
 * for more details.
 *
 * You should have received a copy of the GNU General Public License along
 * with this program; if not, write to the Free Software Foundation, Inc.,
 * 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
 */

#include "openpilot.h"
#include "pios.h"
#include "pios_math.h"
#include <pios_helpers.h>
#include <pios_delay.h>

#if defined(PIOS_INCLUDE_GPS_UBX_PARSER)

#include "inc/UBX.h"
#include "inc/GPS.h"
#include <string.h>

#if !defined(PIOS_GPS_MINIMAL)
#include <auxmagsupport.h>
static bool useMag = false;
#endif /* !defined(PIOS_GPS_MINIMAL) */

// this is set and used by this low level ubx code
// it is also reset by the ubx configuration code (UBX6 vs. UBX7) in ubx_autoconfig.c
GPSPositionSensorSensorTypeOptions ubxSensorType = GPSPOSITIONSENSOR_SENSORTYPE_UNKNOWN;

static bool usePvt = false;
static uint32_t lastPvtTime = 0;

// parse table item
typedef struct {
    uint8_t msgClass;
    uint8_t msgID;
    void (*handler)(struct UBXPacket *, GPSPositionSensorData *GpsPosition);
} ubx_message_handler;

// parsing functions, roughly ordered by reception rate (higher rate messages on top)
static void parse_ubx_nav_posllh(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_nav_velned(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_nav_sol(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_nav_dop(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
#if !defined(PIOS_GPS_MINIMAL)
static void parse_ubx_nav_pvt(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_nav_timeutc(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_nav_svinfo(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_op_sys(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_op_mag(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_ack_ack(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_ack_nak(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
static void parse_ubx_mon_ver(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition);
#endif /* !defined(PIOS_GPS_MINIMAL) */

const ubx_message_handler ubx_handler_table[] = {
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_POSLLH,  .handler = &parse_ubx_nav_posllh  },
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_VELNED,  .handler = &parse_ubx_nav_velned  },
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_SOL,     .handler = &parse_ubx_nav_sol     },
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_DOP,     .handler = &parse_ubx_nav_dop     },
#if !defined(PIOS_GPS_MINIMAL)
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_PVT,     .handler = &parse_ubx_nav_pvt     },
    { .msgClass = UBX_CLASS_OP_CUST, .msgID = UBX_ID_OP_MAG,      .handler = &parse_ubx_op_mag      },
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_SVINFO,  .handler = &parse_ubx_nav_svinfo  },
    { .msgClass = UBX_CLASS_NAV,     .msgID = UBX_ID_NAV_TIMEUTC, .handler = &parse_ubx_nav_timeutc },

    { .msgClass = UBX_CLASS_OP_CUST, .msgID = UBX_ID_OP_SYS,      .handler = &parse_ubx_op_sys      },
    { .msgClass = UBX_CLASS_ACK,     .msgID = UBX_ID_ACK_ACK,     .handler = &parse_ubx_ack_ack     },
    { .msgClass = UBX_CLASS_ACK,     .msgID = UBX_ID_ACK_NAK,     .handler = &parse_ubx_ack_nak     },

    { .msgClass = UBX_CLASS_MON,     .msgID = UBX_ID_MON_VER,     .handler = &parse_ubx_mon_ver     },
#endif /* !defined(PIOS_GPS_MINIMAL) */
};
#define UBX_HANDLER_TABLE_SIZE NELEMENTS(ubx_handler_table)

// detected hw version
int32_t ubxHwVersion = -1;

// Last received Ack/Nak
struct UBX_ACK_ACK ubxLastAck;
struct UBX_ACK_NAK ubxLastNak;

// If a PVT sentence is received in the last UBX_PVT_TIMEOUT (ms) timeframe it disables VELNED/POSLLH/SOL/TIMEUTC
#define UBX_PVT_TIMEOUT (1000)

// parse incoming character stream for messages in UBX binary format
int parse_ubx_stream(uint8_t *rx, uint16_t len, char *gps_rx_buffer, GPSPositionSensorData *GpsData, struct GPS_RX_STATS *gpsRxStats)
{
    enum proto_states {
        START,
        UBX_SY2,
        UBX_CLASS,
        UBX_ID,
        UBX_LEN1,
        UBX_LEN2,
        UBX_PAYLOAD,
        UBX_CHK1,
        UBX_CHK2,
        FINISHED
    };
    enum restart_states {
        RESTART_WITH_ERROR,
        RESTART_NO_ERROR
    };
    static uint16_t rx_count = 0;
    static enum proto_states proto_state = START;
    struct UBXPacket *ubx    = (struct UBXPacket *)gps_rx_buffer;
    int ret = PARSER_INCOMPLETE; // message not (yet) complete
    uint16_t i = 0;
    uint16_t restart_index   = 0;
    enum restart_states restart_state;
    uint8_t c;

    // switch continue is the normal condition and comes back to here for another byte
    // switch break is the error state that branches to the end and restarts the scan at the byte after the first sync byte
    while (i < len) {
        c = rx[i++];
        switch (proto_state) {
        case START: // detect protocol
            if (c == UBX_SYNC1) { // first UBX sync char found
                proto_state   = UBX_SY2;
                // restart here, at byte after SYNC1, if we fail to parse
                restart_index = i;
            }
            continue;
        case UBX_SY2:
            if (c == UBX_SYNC2) { // second UBX sync char found
                proto_state = UBX_CLASS;
            } else {
                restart_state = RESTART_NO_ERROR;
                break;
            }
            continue;
        case UBX_CLASS:
            ubx->header.class = c;
            proto_state      = UBX_ID;
            continue;
        case UBX_ID:
            ubx->header.id   = c;
            proto_state      = UBX_LEN1;
            continue;
        case UBX_LEN1:
            ubx->header.len  = c;
            proto_state      = UBX_LEN2;
            continue;
        case UBX_LEN2:
            ubx->header.len += (c << 8);
            if (ubx->header.len > sizeof(UBXPayload)) {
                gpsRxStats->gpsRxOverflow++;
#if defined(PIOS_GPS_MINIMAL)
                restart_state = RESTART_NO_ERROR;
#else
                restart_state = RESTART_WITH_ERROR;
#endif
                break;
            } else {
                if (ubx->header.len == 0) {
                    proto_state = UBX_CHK1;
                } else {
                    proto_state = UBX_PAYLOAD;
                    rx_count    = 0;
                }
            }
            continue;
        case UBX_PAYLOAD:
            if (rx_count < ubx->header.len) {
                ubx->payload.payload[rx_count] = c;
                if (++rx_count == ubx->header.len) {
                    proto_state = UBX_CHK1;
                }
            }
            continue;
        case UBX_CHK1:
            ubx->header.ck_a = c;
            proto_state = UBX_CHK2;
            continue;
        case UBX_CHK2:
            ubx->header.ck_b = c;
            // OP GPSV9 sends data with bad checksums this appears to happen because it drops data
            // this has been proven by running it without autoconfig and testing:
            // data coming from OPV9 "GPS+MCU" port the checksum errors happen roughly every 5 to 30 seconds
            // same data coming from OPV9 "GPS Only" port the checksums are always good
            // this also occasionally causes parse_ubx_message() to issue alarms because not all the messages were received
            // see OP GPSV9 comment in parse_ubx_message() for further information
            if (checksum_ubx_message(ubx)) {
                gpsRxStats->gpsRxReceived++;
                proto_state = START;
                // overwrite PARSER_INCOMPLETE with PARSER_COMPLETE
                // but don't overwrite PARSER_ERROR with PARSER_COMPLETE
                // pass PARSER_ERROR to caller if it happens even once
                // only pass PARSER_COMPLETE back to caller if we parsed a full set of GPS data
                // that allows the caller to know if we are parsing GPS data
                // or just other packets for some reason (mis-configuration)
                if (parse_ubx_message(ubx, GpsData) == GPSPOSITIONSENSOR_OBJID
                    && ret == PARSER_INCOMPLETE) {
                    ret = PARSER_COMPLETE;
                }
            } else {
                gpsRxStats->gpsRxChkSumError++;
                restart_state = RESTART_WITH_ERROR;
                break;
            }
            continue;
        default:
            continue;
        }

        // this simple restart doesn't work across calls
        // but it does work within a single call
        // and it does the expected thing across calls
        // if restarting due to error detected in 2nd call to this function (on split packet)
        // then we just restart at index 0, which is mid-packet, not the second byte
        if (restart_state == RESTART_WITH_ERROR) {
            ret = PARSER_ERROR; // inform caller that we found at least one error (along with 0 or more good packets)
        }
        rx  += restart_index; // restart parsing just past the most recent SYNC1
        len -= restart_index;
        i    = 0;
        proto_state = START;
    }

    return ret;
}

// Keep track of various GPS messages needed to make up a single UAVO update
// time-of-week timestamp is used to correlate matching messages
#define POSLLH_RECEIVED (1 << 0)
#define STATUS_RECEIVED (1 << 1)
#define DOP_RECEIVED    (1 << 2)
#define VELNED_RECEIVED (1 << 3)
#define SOL_RECEIVED    (1 << 4)
#define ALL_RECEIVED    (SOL_RECEIVED | VELNED_RECEIVED | DOP_RECEIVED | POSLLH_RECEIVED)
#define NONE_RECEIVED   0

static struct msgtracker {
    uint32_t currentTOW; // TOW of the message set currently in progress
    uint8_t  msg_received;   // keep track of received message types
} msgtracker;

// Check if a message belongs to the current data set and register it as 'received'
bool check_msgtracker(uint32_t tow, uint8_t msg_flag)
{
    if (tow > msgtracker.currentTOW ? true // start of a new message set
        : (msgtracker.currentTOW - tow > 6 * 24 * 3600 * 1000)) { // 6 days, TOW wrap around occured
        msgtracker.currentTOW   = tow;
        msgtracker.msg_received = NONE_RECEIVED;
    } else if (tow < msgtracker.currentTOW) { // message outdated (don't process)
        return false;
    }

    msgtracker.msg_received |= msg_flag; // register reception of this msg type
    return true;
}

bool checksum_ubx_message(struct UBXPacket *ubx)
{
    int i;
    uint8_t ck_a, ck_b;

    ck_a  = ubx->header.class;
    ck_b  = ck_a;

    ck_a += ubx->header.id;
    ck_b += ck_a;

    ck_a += ubx->header.len & 0xff;
    ck_b += ck_a;

    ck_a += ubx->header.len >> 8;
    ck_b += ck_a;

    for (i = 0; i < ubx->header.len; i++) {
        ck_a += ubx->payload.payload[i];
        ck_b += ck_a;
    }

    if (ubx->header.ck_a == ck_a &&
        ubx->header.ck_b == ck_b) {
        return true;
    } else {
        return false;
    }
}

static void parse_ubx_nav_posllh(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    if (usePvt) {
        return;
    }
    struct UBX_NAV_POSLLH *posllh = &ubx->payload.nav_posllh;

    if (check_msgtracker(posllh->iTOW, POSLLH_RECEIVED)) {
        if (GpsPosition->Status != GPSPOSITIONSENSOR_STATUS_NOFIX) {
            GpsPosition->Altitude  = (float)posllh->hMSL * 0.001f;
            GpsPosition->GeoidSeparation = (float)(posllh->height - posllh->hMSL) * 0.001f;
            GpsPosition->Latitude  = posllh->lat;
            GpsPosition->Longitude = posllh->lon;
        }
    }
}

static void parse_ubx_nav_sol(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    if (usePvt) {
        return;
    }
    struct UBX_NAV_SOL *sol = &ubx->payload.nav_sol;
    if (check_msgtracker(sol->iTOW, SOL_RECEIVED)) {
        GpsPosition->Satellites = sol->numSV;

        if (sol->flags & STATUS_FLAGS_GPSFIX_OK) {
            switch (sol->gpsFix) {
            case STATUS_GPSFIX_2DFIX:
                GpsPosition->Status = GPSPOSITIONSENSOR_STATUS_FIX2D;
                break;
            case STATUS_GPSFIX_3DFIX:
                GpsPosition->Status = GPSPOSITIONSENSOR_STATUS_FIX3D;
                break;
            default: GpsPosition->Status = GPSPOSITIONSENSOR_STATUS_NOFIX;
            }
        } else { // fix is not valid so we make sure to treat is as NOFIX
            GpsPosition->Status = GPSPOSITIONSENSOR_STATUS_NOFIX;
        }
    }
}

static void parse_ubx_nav_dop(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    struct UBX_NAV_DOP *dop = &ubx->payload.nav_dop;

    if (check_msgtracker(dop->iTOW, DOP_RECEIVED)) {
        GpsPosition->HDOP = (float)dop->hDOP * 0.01f;
        GpsPosition->VDOP = (float)dop->vDOP * 0.01f;
        GpsPosition->PDOP = (float)dop->pDOP * 0.01f;
    }
}

static void parse_ubx_nav_velned(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    if (usePvt) {
        return;
    }
    GPSVelocitySensorData GpsVelocity;
    struct UBX_NAV_VELNED *velned = &ubx->payload.nav_velned;
    if (check_msgtracker(velned->iTOW, VELNED_RECEIVED)) {
        if (GpsPosition->Status != GPSPOSITIONSENSOR_STATUS_NOFIX) {
            GpsVelocity.North        = (float)velned->velN / 100.0f;
            GpsVelocity.East         = (float)velned->velE / 100.0f;
            GpsVelocity.Down         = (float)velned->velD / 100.0f;
            GPSVelocitySensorSet(&GpsVelocity);
            GpsPosition->Groundspeed = (float)velned->gSpeed * 0.01f;
            GpsPosition->Heading     = (float)velned->heading * 1.0e-5f;
        }
    }
}

#if !defined(PIOS_GPS_MINIMAL)
static void parse_ubx_nav_pvt(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    lastPvtTime = PIOS_DELAY_GetuS();

    GPSVelocitySensorData GpsVelocity;
    struct UBX_NAV_PVT *pvt = &ubx->payload.nav_pvt;
    check_msgtracker(pvt->iTOW, (ALL_RECEIVED));

    GpsVelocity.North = (float)pvt->velN * 0.001f;
    GpsVelocity.East  = (float)pvt->velE * 0.001f;
    GpsVelocity.Down  = (float)pvt->velD * 0.001f;
    GPSVelocitySensorSet(&GpsVelocity);

    GpsPosition->Groundspeed     = (float)pvt->gSpeed * 0.001f;
    GpsPosition->Heading         = (float)pvt->heading * 1.0e-5f;
    GpsPosition->Altitude        = (float)pvt->hMSL * 0.001f;
    GpsPosition->GeoidSeparation = (float)(pvt->height - pvt->hMSL) * 0.001f;
    GpsPosition->Latitude        = pvt->lat;
    GpsPosition->Longitude       = pvt->lon;
    GpsPosition->Satellites      = pvt->numSV;
    GpsPosition->PDOP = pvt->pDOP * 0.01f;
    if (pvt->flags & PVT_FLAGS_GNSSFIX_OK) {
        GpsPosition->Status = pvt->fixType == PVT_FIX_TYPE_3D ?
                              GPSPOSITIONSENSOR_STATUS_FIX3D : GPSPOSITIONSENSOR_STATUS_FIX2D;
    } else {
        GpsPosition->Status = GPSPOSITIONSENSOR_STATUS_NOFIX;
    }

    if (pvt->valid & PVT_VALID_VALIDTIME) {
        // Time is valid, set GpsTime
        GPSTimeData GpsTime;

        GpsTime.Year   = pvt->year;
        GpsTime.Month  = pvt->month;
        GpsTime.Day    = pvt->day;
        GpsTime.Hour   = pvt->hour;
        GpsTime.Minute = pvt->min;
        GpsTime.Second = pvt->sec;

        GPSTimeSet(&GpsTime);
    }
}

static void parse_ubx_nav_timeutc(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    if (usePvt) {
        return;
    }

    struct UBX_NAV_TIMEUTC *timeutc = &ubx->payload.nav_timeutc;
    // Test if time is valid
    if ((timeutc->valid & TIMEUTC_VALIDTOW) && (timeutc->valid & TIMEUTC_VALIDWKN)) {
        // Time is valid, set GpsTime
        GPSTimeData GpsTime;

        GpsTime.Year   = timeutc->year;
        GpsTime.Month  = timeutc->month;
        GpsTime.Day    = timeutc->day;
        GpsTime.Hour   = timeutc->hour;
        GpsTime.Minute = timeutc->min;
        GpsTime.Second = timeutc->sec;

        GPSTimeSet(&GpsTime);
    } else {
        // Time is not valid, nothing to do
        return;
    }
}

static void parse_ubx_nav_svinfo(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    uint8_t chan;
    GPSSatellitesData svdata;
    struct UBX_NAV_SVINFO *svinfo = &ubx->payload.nav_svinfo;

    svdata.SatsInView = 0;

    // First, use slots for SVs actually being received
    for (chan = 0; chan < svinfo->numCh; chan++) {
        if (svdata.SatsInView < GPSSATELLITES_PRN_NUMELEM && svinfo->sv[chan].cno > 0) {
            svdata.Azimuth[svdata.SatsInView]   = svinfo->sv[chan].azim;
            svdata.Elevation[svdata.SatsInView] = svinfo->sv[chan].elev;
            svdata.PRN[svdata.SatsInView] = svinfo->sv[chan].svid;
            svdata.SNR[svdata.SatsInView] = svinfo->sv[chan].cno;
            svdata.SatsInView++;
        }
    }

    // Now try to add the rest
    for (chan = 0; chan < svinfo->numCh; chan++) {
        if (svdata.SatsInView < GPSSATELLITES_PRN_NUMELEM && 0 == svinfo->sv[chan].cno) {
            svdata.Azimuth[svdata.SatsInView]   = svinfo->sv[chan].azim;
            svdata.Elevation[svdata.SatsInView] = svinfo->sv[chan].elev;
            svdata.PRN[svdata.SatsInView] = svinfo->sv[chan].svid;
            svdata.SNR[svdata.SatsInView] = svinfo->sv[chan].cno;
            svdata.SatsInView++;
        }
    }

    // fill remaining slots (if any)
    for (chan = svdata.SatsInView; chan < GPSSATELLITES_PRN_NUMELEM; chan++) {
        svdata.Azimuth[chan]   = 0;
        svdata.Elevation[chan] = 0;
        svdata.PRN[chan] = 0;
        svdata.SNR[chan] = 0;
    }

    GPSSatellitesSet(&svdata);
}

static void parse_ubx_ack_ack(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    struct UBX_ACK_ACK *ack_ack = &ubx->payload.ack_ack;

    ubxLastAck = *ack_ack;
}

static void parse_ubx_ack_nak(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    struct UBX_ACK_NAK *ack_nak = &ubx->payload.ack_nak;

    ubxLastNak = *ack_nak;
}

static void parse_ubx_mon_ver(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    struct UBX_MON_VER *mon_ver = &ubx->payload.mon_ver;

    ubxHwVersion  = atoi(mon_ver->hwVersion);
    ubxSensorType = (ubxHwVersion >= UBX_HW_VERSION_8) ? GPSPOSITIONSENSOR_SENSORTYPE_UBX8 :
                    ((ubxHwVersion >= UBX_HW_VERSION_7) ? GPSPOSITIONSENSOR_SENSORTYPE_UBX7 : GPSPOSITIONSENSOR_SENSORTYPE_UBX);
    // send sensor type right now because on UBX NEMA we don't get a full set of messages
    // and we want to be able to see sensor type even on UBX NEMA GPS's
    GPSPositionSensorSensorTypeSet((uint8_t *)&ubxSensorType);
}

static void parse_ubx_op_sys(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    struct UBX_OP_SYSINFO *sysinfo = &ubx->payload.op_sysinfo;
    GPSExtendedStatusData data;

    data.FlightTime   = sysinfo->flightTime;
    data.BoardType[0] = sysinfo->board_type;
    data.BoardType[1] = sysinfo->board_revision;
    memcpy(&data.FirmwareHash, &sysinfo->sha1sum, GPSEXTENDEDSTATUS_FIRMWAREHASH_NUMELEM);
    memcpy(&data.FirmwareTag, &sysinfo->commit_tag_name, GPSEXTENDEDSTATUS_FIRMWARETAG_NUMELEM);
    data.Options = sysinfo->options;
    data.Status  = GPSEXTENDEDSTATUS_STATUS_GPSV9;
    GPSExtendedStatusSet(&data);
}

static void parse_ubx_op_mag(struct UBXPacket *ubx, __attribute__((unused)) GPSPositionSensorData *GpsPosition)
{
    if (!useMag) {
        return;
    }
    struct UBX_OP_MAG *mag = &ubx->payload.op_mag;
    float mags[3] = { mag->x, mag->y, mag->z };
    auxmagsupport_publish_samples(mags, AUXMAGSENSOR_STATUS_OK);
}
#endif /* if !defined(PIOS_GPS_MINIMAL) */

// UBX message parser
// returns UAVObjectID if a UAVObject structure is ready for further processing
uint32_t parse_ubx_message(struct UBXPacket *ubx, GPSPositionSensorData *GpsPosition)
{
    uint32_t id = 0;
    static bool ubxInitialized = false;

    if (!ubxInitialized) {
        // initialize dop values. If no DOP sentence is received it is safer to initialize them to a high value rather than 0.
        GpsPosition->HDOP = 99.99f;
        GpsPosition->PDOP = 99.99f;
        GpsPosition->VDOP = 99.99f;
        ubxInitialized    = true;
    }
    // is it using PVT?
    usePvt = (lastPvtTime) && (PIOS_DELAY_GetuSSince(lastPvtTime) < UBX_PVT_TIMEOUT * 1000);
    for (uint8_t i = 0; i < UBX_HANDLER_TABLE_SIZE; i++) {
        const ubx_message_handler *handler = &ubx_handler_table[i];
        if (handler->msgClass == ubx->header.class && handler->msgID == ubx->header.id) {
            handler->handler(ubx, GpsPosition);
            break;
        }
    }

    GpsPosition->SensorType = ubxSensorType;

    if (msgtracker.msg_received == ALL_RECEIVED) {
        // leave BaudRate field alone!
        GPSPositionSensorBaudRateGet(&GpsPosition->BaudRate);
        GPSPositionSensorSet(GpsPosition);
        msgtracker.msg_received = NONE_RECEIVED;
        id = GPSPOSITIONSENSOR_OBJID;
    } else {
        uint8_t status;
        GPSPositionSensorStatusGet(&status);
        if (status == GPSPOSITIONSENSOR_STATUS_NOGPS) {
            // Some ubx thing has been received so GPS is there
            //
            // OP GPSV9 will sometimes cause this NOFIX
            // because GPSV9 drops data which causes checksum errors which causes GPS.c to set the status to NOGPS
            // see OP GPSV9 comment in parse_ubx_stream() for further information
            status = GPSPOSITIONSENSOR_STATUS_NOFIX;
            GPSPositionSensorStatusSet(&status);
        }
    }
    return id;
}

#if !defined(PIOS_GPS_MINIMAL)
void op_gpsv9_load_mag_settings()
{
    if (auxmagsupport_get_type() == AUXMAGSETTINGS_TYPE_GPSV9) {
        useMag = true;
    } else {
        useMag = false;
    }
}
#endif // !defined(PIOS_GPS_MINIMAL)
#endif // defined(PIOS_INCLUDE_GPS_UBX_PARSER)