xref: /aosp_15_r20/hardware/interfaces/gnss/1.0/IGnssMeasurementCallback.hal (revision 4d7e907c777eeecc4c5bd7cf640a754fac206ff7)

/*
 * Copyright (C) 2016 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package [email protected];

/** The callback interface to report measurements from the HAL. */
interface IGnssMeasurementCallback {
    /**
     * Flags to indicate what fields in GnssClock are valid.
     */
    @export(name="", value_prefix="GNSS_CLOCK_")
    enum GnssClockFlags : uint16_t {
        /** A valid 'leap second' is stored in the data structure. */
        HAS_LEAP_SECOND        = 1 << 0,
        /** A valid 'time uncertainty' is stored in the data structure. */
        HAS_TIME_UNCERTAINTY   = 1 << 1,
        /** A valid 'full bias' is stored in the data structure. */
        HAS_FULL_BIAS          = 1 << 2,
        /** A valid 'bias' is stored in the data structure. */
        HAS_BIAS               = 1 << 3,
        /** A valid 'bias uncertainty' is stored in the data structure. */
        HAS_BIAS_UNCERTAINTY   = 1 << 4,
        /** A valid 'drift' is stored in the data structure. */
        HAS_DRIFT              = 1 << 5,
        /** A valid 'drift uncertainty' is stored in the data structure. */
        HAS_DRIFT_UNCERTAINTY  = 1 << 6
    };

    /**
     * Flags to indicate what fields in GnssMeasurement are valid.
     */
    @export(name="", value_prefix="GNSS_MEASUREMENT_")
    enum GnssMeasurementFlags : uint32_t {
        /** A valid 'snr' is stored in the data structure. */
        HAS_SNR                        = 1 << 0,
        /** A valid 'carrier frequency' is stored in the data structure. */
        HAS_CARRIER_FREQUENCY          = 1 << 9,
        /** A valid 'carrier cycles' is stored in the data structure. */
        HAS_CARRIER_CYCLES             = 1 << 10,
        /** A valid 'carrier phase' is stored in the data structure. */
        HAS_CARRIER_PHASE              = 1 << 11,
        /** A valid 'carrier phase uncertainty' is stored in the data structure. */
        HAS_CARRIER_PHASE_UNCERTAINTY  = 1 << 12,
        /** A valid automatic gain control is stored in the data structure. */
        HAS_AUTOMATIC_GAIN_CONTROL     = 1 << 13
    };

    /**
     * Enumeration of available values for the GNSS Measurement's multipath
     * indicator.
     */
    @export(name="", value_prefix="GNSS_MULTIPATH_")
    enum GnssMultipathIndicator : uint8_t {
        /** The indicator is not available or unknown. */
        INDICATOR_UNKNOWN      = 0,
        /** The measurement is indicated to be affected by multipath. */
        INDICATOR_PRESENT      = 1,
        /** The measurement is indicated to be not affected by multipath. */
        INDICATIOR_NOT_PRESENT = 2
    };

    /**
     * Flags indicating the GNSS measurement state.
     *
     * The expected behavior here is for GNSS HAL to set all the flags that applies.
     * For example, if the state for a satellite is only C/A code locked and bit
     * synchronized, and there is still millisecond ambiguity, the state must be
     * set as:
     *
     * STATE_CODE_LOCK | STATE_BIT_SYNC |  STATE_MSEC_AMBIGUOUS
     *
     * If GNSS is still searching for a satellite, the corresponding state must be
     * set to STATE_UNKNOWN(0).
     */
    @export(name="", value_prefix="GNSS_MEASUREMENT_")
    enum GnssMeasurementState : uint32_t {
        STATE_UNKNOWN                = 0,
        STATE_CODE_LOCK              = 1 << 0,
        STATE_BIT_SYNC               = 1 << 1,
        STATE_SUBFRAME_SYNC          = 1 << 2,
        STATE_TOW_DECODED            = 1 << 3,
        STATE_MSEC_AMBIGUOUS         = 1 << 4,
        STATE_SYMBOL_SYNC            = 1 << 5,
        STATE_GLO_STRING_SYNC        = 1 << 6,
        STATE_GLO_TOD_DECODED        = 1 << 7,
        STATE_BDS_D2_BIT_SYNC        = 1 << 8,
        STATE_BDS_D2_SUBFRAME_SYNC   = 1 << 9,
        STATE_GAL_E1BC_CODE_LOCK     = 1 << 10,
        STATE_GAL_E1C_2ND_CODE_LOCK  = 1 << 11,
        STATE_GAL_E1B_PAGE_SYNC      = 1 << 12,
        STATE_SBAS_SYNC              = 1 << 13,
        STATE_TOW_KNOWN              = 1 << 14,
        STATE_GLO_TOD_KNOWN          = 1 << 15,
    };

     /**
     * Flags indicating the Accumulated Delta Range's states.
     *
     * See the table below for a detailed interpretation of each state.
     *
     * +---------------------+-------------------+-----------------------------+
     * | ADR_STATE           | Time of relevance | Interpretation              |
     * +---------------------+-------------------+-----------------------------+
     * | UNKNOWN             | ADR(t)            | No valid carrier phase      |
     * |                     |                   | information is available    |
     * |                     |                   | at time t.                  |
     * +---------------------+-------------------+-----------------------------+
     * | VALID               | ADR(t)            | Valid carrier phase         |
     * |                     |                   | information is available    |
     * |                     |                   | at time t. This indicates   |
     * |                     |                   | that this measurement can   |
     * |                     |                   | be used as a reference for  |
     * |                     |                   | future measurements.        |
     * |                     |                   | However, to compare it to   |
     * |                     |                   | previous measurements to    |
     * |                     |                   | compute delta range,        |
     * |                     |                   | other bits should be        |
     * |                     |                   | checked. Specifically, it   |
     * |                     |                   | can be used for delta range |
     * |                     |                   | computation if it is valid  |
     * |                     |                   | and has no reset or cycle   |
     * |                     |                   | slip at this epoch i.e.     |
     * |                     |                   | if VALID_BIT == 1 &&        |
     * |                     |                   | CYCLE_SLIP_BIT == 0 &&      |
     * |                     |                   | RESET_BIT == 0.             |
     * +---------------------+-------------------+-----------------------------+
     * | RESET               | ADR(t) - ADR(t-1) | Carrier phase accumulation  |
     * |                     |                   | has been restarted between  |
     * |                     |                   | current time t and previous |
     * |                     |                   | time t-1. This indicates    |
     * |                     |                   | that this measurement can   |
     * |                     |                   | be used as a reference for  |
     * |                     |                   | future measurements, but it |
     * |                     |                   | should not be compared to   |
     * |                     |                   | previous measurements to    |
     * |                     |                   | compute delta range.        |
     * +---------------------+-------------------+-----------------------------+
     * | CYCLE_SLIP          | ADR(t) - ADR(t-1) | Cycle slip(s) have been     |
     * |                     |                   | detected between the        |
     * |                     |                   | current time t and previous |
     * |                     |                   | time t-1. This indicates    |
     * |                     |                   | that this measurement can   |
     * |                     |                   | be used as a reference for  |
     * |                     |                   | future measurements.        |
     * |                     |                   | Clients can use a           |
     * |                     |                   | measurement with a cycle    |
     * |                     |                   | slip to compute delta range |
     * |                     |                   | against previous            |
     * |                     |                   | measurements at their own   |
     * |                     |                   | risk.                       |
     * +---------------------+-------------------+-----------------------------+
     *
     */
    @export(name="", value_prefix="GNSS_")
    enum GnssAccumulatedDeltaRangeState : uint16_t {
        ADR_STATE_UNKNOWN    = 0,
        ADR_STATE_VALID      = 1 << 0,
        ADR_STATE_RESET      = 1 << 1,
        ADR_STATE_CYCLE_SLIP = 1 << 2,
    };

    /**
     * Represents an estimate of the GNSS clock time.
     */
    struct GnssClock {
        /**
         * A set of flags indicating the validity of the fields in this data
         * structure.
         *
         * Fields for which there is no corresponding flag must be filled in
         * with a valid value.  For convenience, these are marked as mandatory.
         *
         * Others fields may have invalid information in them, if not marked as
         * valid by the corresponding bit in gnssClockFlags.
         */
        bitfield<GnssClockFlags> gnssClockFlags;

        /**
         * Leap second data.
         * The sign of the value is defined by the following equation:
         *      utcTimeNs = timeNs - (fullBiasNs + biasNs) - leapSecond *
         *      1,000,000,000
         *
         * If this data is available, gnssClockFlags must contain
         * HAS_LEAP_SECOND.
         */
        int16_t leapSecond;

        /**
         * The GNSS receiver internal clock value. This is the local hardware clock
         * value.
         *
         * For local hardware clock, this value is expected to be monotonically
         * increasing while the hardware clock remains powered on. (For the case of a
         * HW clock that is not continuously on, see the
         * hwClockDiscontinuityCount field). The receiver's estimate of GNSS time
         * can be derived by subtracting the sum of fullBiasNs and biasNs (when
         * available) from this value.
         *
         * This GNSS time must be the best estimate of current GNSS time
         * that GNSS receiver can achieve.
         *
         * Sub-nanosecond accuracy can be provided by means of the 'biasNs' field.
         * The value contains the timeUncertaintyNs in it.
         *
         * This value is mandatory.
         */
        int64_t timeNs;

        /**
         * 1-Sigma uncertainty associated with the clock's time in nanoseconds.
         * The uncertainty is represented as an absolute (single sided) value.
         *
         * If the data is available, gnssClockFlags must contain
         * HAS_TIME_UNCERTAINTY. Ths value is ideally zero, as the time
         * 'latched' by timeNs is defined as the reference clock vs. which all
         * other times (and corresponding uncertainties) are measured.
         */
        double timeUncertaintyNs;

        /**
         * The difference between hardware clock ('time' field) inside GNSS receiver
         * and the true GPS time since 0000Z, January 6, 1980, in nanoseconds.
         *
         * The sign of the value is defined by the following equation:
         *      local estimate of GPS time = timeNs - (fullBiasNs + biasNs)
         *
         * If receiver has computed time for a non-GPS constellation, the time offset of
         * that constellation versus GPS time must be applied to fill this value.
         *
         * The error estimate for the sum of this and the biasNs is the biasUncertaintyNs.
         *
         * If the data is available gnssClockFlags must contain HAS_FULL_BIAS.
         *
         * This value is mandatory if the receiver has estimated GPS time.
         */
        int64_t fullBiasNs;

        /**
         * Sub-nanosecond bias - used with fullBiasNS, see fullBiasNs for details.
         *
         * The error estimate for the sum of this and the fullBiasNs is the
         * biasUncertaintyNs.
         *
         * If the data is available gnssClockFlags must contain HAS_BIAS.
         *
         * This value is mandatory if the receiver has estimated GPS time.
         */
        double biasNs;

        /**
         * 1-Sigma uncertainty associated with the local estimate of GNSS time (clock
         * bias) in nanoseconds. The uncertainty is represented as an absolute
         * (single sided) value.
         *
         * The caller is responsible for using this uncertainty (it can be very
         * large before the GPS time has been fully resolved.)
         *
         * If the data is available gnssClockFlags must contain HAS_BIAS_UNCERTAINTY.
         *
         * This value is mandatory if the receiver has estimated GPS time.
         */
        double biasUncertaintyNs;

        /**
         * The clock's drift in nanoseconds (per second).
         *
         * A positive value means that the frequency is higher than the nominal
         * frequency, and that the (fullBiasNs + biasNs) is growing more positive
         * over time.
         *
         * If the data is available gnssClockFlags must contain HAS_DRIFT.
         *
         * This value is mandatory if the receiver has estimated GPS time.
         */
        double driftNsps;

        /**
         * 1-Sigma uncertainty associated with the clock's drift in nanoseconds (per
         * second).
         * The uncertainty is represented as an absolute (single sided) value.
         *
         * If the data is available gnssClockFlags must contain HAS_DRIFT_UNCERTAINTY.
         *
         * This value is mandatory if the receiver has estimated GPS time.
         */
        double driftUncertaintyNsps;

        /**
         * This field must be incremented, when there are discontinuities in the
         * hardware clock.
         *
         * A "discontinuity" is meant to cover the case of a switch from one source
         * of clock to another.  A single free-running crystal oscillator (XO)
         * will generally not have any discontinuities, and this can be set and
         * left at 0.
         *
         * If, however, the timeNs value (HW clock) is derived from a composite of
         * sources, that is not as smooth as a typical XO, or is otherwise stopped &
         * restarted, then this value shall be incremented each time a discontinuity
         * occurs.  (E.g. this value can start at zero at device boot-up and
         * increment each time there is a change in clock continuity. In the
         * unlikely event that this value reaches full scale, rollover (not
         * clamping) is required, such that this value continues to change, during
         * subsequent discontinuity events.)
         *
         * While this number stays the same, between GnssClock reports, it can be
         * safely assumed that the timeNs value has been running continuously, e.g.
         * derived from a single, high quality clock (XO like, or better, that is
         * typically used during continuous GNSS signal sampling.)
         *
         * It is expected, esp. during periods where there are few GNSS signals
         * available, that the HW clock be discontinuity-free as long as possible,
         * as this avoids the need to use (waste) a GNSS measurement to fully
         * re-solve for the GNSS clock bias and drift, when using the accompanying
         * measurements, from consecutive GnssData reports.
         *
         * This value is mandatory.
         */
        uint32_t hwClockDiscontinuityCount;

    };

    /**
     * Represents a GNSS Measurement, it contains raw and computed information.
     *
     * All signal measurement information (e.g. svTime,
     * pseudorangeRate, multipathIndicator) reported in this struct must be
     * based on GNSS signal measurements only. You must not synthesize measurements
     * by calculating or reporting expected measurements based on known or estimated
     * position, velocity, or time.
     */
    struct GnssMeasurement{
        /**
         * A set of flags indicating the validity of the fields in this data
         * structure.
         *
         * Fields for which there is no corresponding flag must be filled in
         * with a valid value.  For convenience, these are marked as mandatory.
         *
         * Others fields may have invalid information in them, if not marked as
         * valid by the corresponding bit in flags.
         */
        bitfield<GnssMeasurementFlags> flags;

        /**
         * Satellite vehicle ID number, as defined in GnssSvInfo::svid
         *
         * This value is mandatory.
         */
        int16_t svid;

        /**
         * Defines the constellation of the given SV.
         *
         * This value is mandatory.
         */
        GnssConstellationType constellation;

        /**
         * Time offset at which the measurement was taken in nanoseconds.
         * The reference receiver's time is specified by GnssData::clock::timeNs.
         *
         * The sign of timeOffsetNs is given by the following equation:
         *      measurement time = GnssClock::timeNs + timeOffsetNs
         *
         * It provides an individual time-stamp for the measurement, and allows
         * sub-nanosecond accuracy. It may be zero if all measurements are
         * aligned to a common time.
         *
         * This value is mandatory.
         */
        double timeOffsetNs;

        /**
         * Per satellite sync state. It represents the current sync state for the
         * associated satellite.
         * Based on the sync state, the 'received GNSS tow' field must be interpreted
         * accordingly.
         *
         * This value is mandatory.
         */
        bitfield<GnssMeasurementState> state;

        /**
         * The received GNSS Time-of-Week at the measurement time, in nanoseconds.
         * For GNSS & QZSS, this is the received GNSS Time-of-Week at the
         * measurement time, in nanoseconds. The value is relative to the
         * beginning of the current GNSS week.
         *
         * Given the highest sync state that can be achieved, per each satellite,
         * valid range for this field can be:
         * Searching       : [ 0       ] : STATE_UNKNOWN
         * C/A code lock   : [ 0 1ms   ] : STATE_CODE_LOCK set
         * Bit sync        : [ 0 20ms  ] : STATE_BIT_SYNC set
         * Subframe sync   : [ 0  6s   ] : STATE_SUBFRAME_SYNC set
         * TOW decoded     : [ 0 1week ] : STATE_TOW_DECODED set
         * TOW Known       : [ 0 1week ] : STATE_TOW_KNOWN set
         *
         * Note: TOW Known refers to the case where TOW is possibly not decoded
         * over the air but has been determined from other sources. If TOW
         * decoded is set then TOW Known must also be set.
         *
         * Note: If there is any ambiguity in integer millisecond,
         * GNSS_MEASUREMENT_STATE_MSEC_AMBIGUOUS must be set accordingly, in the
         * 'state' field.
         *
         * This value must be populated if 'state' != STATE_UNKNOWN.
         *
         * For Glonass, this is the received Glonass time of day, at the
         * measurement time in nanoseconds.
         *
         * Given the highest sync state that can be achieved, per each satellite,
         * valid range for this field can be:
         * Searching           : [ 0       ] : STATE_UNKNOWN set
         * C/A code lock       : [ 0   1ms ] : STATE_CODE_LOCK set
         * Symbol sync         : [ 0  10ms ] : STATE_SYMBOL_SYNC set
         * Bit sync            : [ 0  20ms ] : STATE_BIT_SYNC set
         * String sync         : [ 0    2s ] : STATE_GLO_STRING_SYNC set
         * Time of day decoded : [ 0  1day ] : STATE_GLO_TOD_DECODED set
         * Time of day known   : [ 0  1day ] : STATE_GLO_TOD_KNOWN set
         *
         * Note: Time of day known refers to the case where it is possibly not
         * decoded over the air but has been determined from other sources. If
         * Time of day decoded is set then Time of day known must also be set.
         *
         * For Beidou, this is the received Beidou time of week,
         * at the measurement time in nanoseconds.
         *
         * Given the highest sync state that can be achieved, per each satellite,
         * valid range for this field can be:
         * Searching            : [ 0       ] : STATE_UNKNOWN set.
         * C/A code lock        : [ 0   1ms ] : STATE_CODE_LOCK set.
         * Bit sync (D2)        : [ 0   2ms ] : STATE_BDS_D2_BIT_SYNC set.
         * Bit sync (D1)        : [ 0  20ms ] : STATE_BIT_SYNC set.
         * Subframe (D2)        : [ 0  0.6s ] : STATE_BDS_D2_SUBFRAME_SYNC set.
         * Subframe (D1)        : [ 0    6s ] : STATE_SUBFRAME_SYNC set.
         * Time of week decoded : [ 0 1week ] : STATE_TOW_DECODED set.
         * Time of week known   : [ 0 1week ] : STATE_TOW_KNOWN set
         *
         * Note: TOW Known refers to the case where TOW is possibly not decoded
         * over the air but has been determined from other sources. If TOW
         * decoded is set then TOW Known must also be set.
         *
         * For Galileo, this is the received Galileo time of week,
         * at the measurement time in nanoseconds.
         *
         * E1BC code lock       : [ 0  4ms ] : STATE_GAL_E1BC_CODE_LOCK set.
         * E1C 2nd code lock    : [ 0 100ms] : STATE_GAL_E1C_2ND_CODE_LOCK set.
         * E1B page             : [ 0   2s ] : STATE_GAL_E1B_PAGE_SYNC set.
         * Time of week decoded : [ 0 1week] : STATE_TOW_DECODED is set.
         * Time of week known   : [ 0 1week] : STATE_TOW_KNOWN set
         *
         * Note: TOW Known refers to the case where TOW is possibly not decoded
         * over the air but has been determined from other sources. If TOW
         * decoded is set then TOW Known must also be set.
         *
         * For SBAS, this is received SBAS time, at the measurement time in
         * nanoseconds.
         *
         * Given the highest sync state that can be achieved, per each satellite,
         * valid range for this field can be:
         * Searching    : [ 0     ] : STATE_UNKNOWN
         * C/A code lock: [ 0 1ms ] : STATE_CODE_LOCK is set
         * Symbol sync  : [ 0 2ms ] : STATE_SYMBOL_SYNC is set
         * Message      : [ 0  1s ] : STATE_SBAS_SYNC is set
         */
        int64_t receivedSvTimeInNs;

        /**
         * 1-Sigma uncertainty of the Received GNSS Time-of-Week in nanoseconds.
         *
         * This value must be populated if 'state' != STATE_UNKNOWN.
         */
        int64_t receivedSvTimeUncertaintyInNs;

        /**
         * Carrier-to-noise density in dB-Hz, typically in the range [0, 63].
         * It contains the measured C/N0 value for the signal at the antenna port.
         *
         * If a signal has separate components (e.g. Pilot and Data channels) and
         * the receiver only processes one of the components, then the reported
         * cN0DbHz reflects only the component that is processed.
         *
         * This value is mandatory.
         */
        double cN0DbHz;

        /**
         * Pseudorange rate at the timestamp in m/s. The correction of a given
         * Pseudorange Rate value includes corrections for receiver and satellite
         * clock frequency errors. Ensure that this field is independent (see
         * comment at top of GnssMeasurement struct.)
         *
         * It is mandatory to provide the 'uncorrected' 'pseudorange rate', and
         * provide GnssClock's 'drift' field as well. When providing the
         * uncorrected pseudorange rate, do not apply the corrections described above.)
         *
         * The value includes the 'pseudorange rate uncertainty' in it.
         * A positive 'uncorrected' value indicates that the SV is moving away from
         * the receiver.
         *
         * The sign of the 'uncorrected' 'pseudorange rate' and its relation to the
         * sign of 'doppler shift' is given by the equation:
         *      pseudorange rate = -k * doppler shift   (where k is a constant)
         *
         * This must be the most accurate pseudorange rate available, based on
         * fresh signal measurements from this channel.
         *
         * It is mandatory that this value be provided at typical carrier phase PRR
         * quality (few cm/sec per second of uncertainty, or better) - when signals
         * are sufficiently strong & stable, e.g. signals from a GNSS simulator at >=
         * 35 dB-Hz.
         */
        double pseudorangeRateMps;

        /**
         * 1-Sigma uncertainty of the pseudorangeRateMps.
         * The uncertainty is represented as an absolute (single sided) value.
         *
         * This value is mandatory.
         */
        double pseudorangeRateUncertaintyMps;

        /**
         * Accumulated delta range's state. It indicates whether ADR is reset or
         * there is a cycle slip(indicating loss of lock).
         *
         * This value is mandatory.
         */
        bitfield<GnssAccumulatedDeltaRangeState> accumulatedDeltaRangeState;

        /**
         * Accumulated delta range since the last channel reset in meters.
         * A positive value indicates that the SV is moving away from the receiver.
         *
         * The sign of the 'accumulated delta range' and its relation to the sign of
         * 'carrier phase' is given by the equation:
         * accumulated delta range = -k * carrier phase (where k is a constant)
         *
         * This value must be populated if 'accumulated delta range state' !=
         * ADR_STATE_UNKNOWN.
         * However, it is expected that the data is only accurate when:
         *      'accumulated delta range state' == ADR_STATE_VALID.
         */
        double accumulatedDeltaRangeM;

        /**
         * 1-Sigma uncertainty of the accumulated delta range in meters.
         * This value must be populated if 'accumulated delta range state' !=
         * ADR_STATE_UNKNOWN.
         */
        double accumulatedDeltaRangeUncertaintyM;

        /**
         * Carrier frequency of the signal tracked, for example it can be the
         * GPS central frequency for L1 = 1575.45 MHz, or L2 = 1227.60 MHz, L5 =
         * 1176.45 MHz, varying GLO channels, etc. If the field is not set, it
         * is the primary common use central frequency, e.g. L1 = 1575.45 MHz
         * for GPS.
         *
         * For an L1, L5 receiver tracking a satellite on L1 and L5 at the same
         * time, two raw measurement structs must be reported for this same
         * satellite, in one of the measurement structs, all the values related
         * to L1 must be filled, and in the other all of the values related to
         * L5 must be filled.
         *
         * If the data is available, gnssMeasurementFlags must contain
         * HAS_CARRIER_FREQUENCY.
         */
        float carrierFrequencyHz;

        /**
         * The number of full carrier cycles between the satellite and the
         * receiver. The reference frequency is given by the field
         * 'carrierFrequencyHz'. Indications of possible cycle slips and
         * resets in the accumulation of this value can be inferred from the
         * accumulatedDeltaRangeState flags.
         *
         * If the data is available, gnssMeasurementFlags must contain
         * HAS_CARRIER_CYCLES.
         */
        int64_t carrierCycles;

        /**
         * The RF phase detected by the receiver, in the range [0.0, 1.0].
         * This is usually the fractional part of the complete carrier phase
         * measurement.
         *
         * The reference frequency is given by the field 'carrierFrequencyHz'.
         * The value contains the 'carrier-phase uncertainty' in it.
         *
         * If the data is available, gnssMeasurementFlags must contain
         * HAS_CARRIER_PHASE.
         */
        double carrierPhase;

        /**
         * 1-Sigma uncertainty of the carrier-phase.
         * If the data is available, gnssMeasurementFlags must contain
         * HAS_CARRIER_PHASE_UNCERTAINTY.
         */
        double carrierPhaseUncertainty;

        /**
         * An enumeration that indicates the 'multipath' state of the event.
         *
         * The multipath Indicator is intended to report the presence of overlapping
         * signals that manifest as distorted correlation peaks.
         *
         * - if there is a distorted correlation peak shape, report that multipath
         *   is MULTIPATH_INDICATOR_PRESENT.
         * - if there is no distorted correlation peak shape, report
         *   MULTIPATH_INDICATOR_NOT_PRESENT
         * - if signals are too weak to discern this information, report
         *   MULTIPATH_INDICATOR_UNKNOWN
         *
         * Example: when doing the standardized overlapping Multipath Performance
         * test (3GPP TS 34.171) the Multipath indicator must report
         * MULTIPATH_INDICATOR_PRESENT for those signals that are tracked, and
         * contain multipath, and MULTIPATH_INDICATOR_NOT_PRESENT for those
         * signals that are tracked and do not contain multipath.
         */
        GnssMultipathIndicator multipathIndicator;

        /**
         * Signal-to-noise ratio at correlator output in dB.
         * If the data is available, GnssMeasurementFlags must contain HAS_SNR.
         * This is the power ratio of the "correlation peak height above the
         * observed noise floor" to "the noise RMS".
         */
        double snrDb;


    /**
     * Automatic gain control (AGC) level. AGC acts as a variable gain amplifier adjusting the power
     * of the incoming signal. The AGC level may be used to indicate potential interference. Higher
     * gain (and/or lower input power) must be output as a positive number. Hence in cases of strong
     * jamming, in the band of this signal, this value must go more negative. This value must be
     * consistent given the same level of the incoming signal power.
     *
     * Note: Different hardware designs (e.g. antenna, pre-amplification, or other RF HW components)
     * may also affect the typical output of this value on any given hardware design in an open sky
     * test - the important aspect of this output is that changes in this value are indicative of
     * changes on input signal power in the frequency band for this measurement.
     */
        double agcLevelDb;
    };

    /**
     * Represents a reading of GNSS measurements. For devices where GnssSystemInfo's
     * yearOfHw is set to 2016+, it is mandatory that these be provided, on
     * request, when the GNSS receiver is searching/tracking signals.
     *
     * - Reporting of GNSS constellation measurements is mandatory.
     * - Reporting of all tracked constellations are encouraged.
     */
    struct GnssData {
        /** Number of GnssMeasurement elements. */
        uint32_t measurementCount;

        /** The array of measurements. */
        GnssMeasurement[GnssMax:SVS_COUNT] measurements;

        /** The GNSS clock time reading. */
        GnssClock clock;
    };

    /**
     * Callback for the hal to pass a GnssData structure back to the client.
     *
     * @param data Contains a reading of GNSS measurements.
     */
    GnssMeasurementCb(GnssData data);
};