GNSS

Global positioning module with NMEA 0183 protocol support. Contains data structures, initialization code, validation functions, and UART configuration for the GY-NEO6MV2 sensor.

Hardware Specifications

GPS Fix Quality Types

typedef enum {
    GPS_NO_FIX = 0,        // No GPS fix available
    GPS_GPS_FIX = 1,       // Standard GPS fix
    GPS_DGPS_FIX = 2,      // Differential GPS fix
    GPS_PPS_FIX = 3,       // PPS (Pulse Per Second) fix
    GPS_RTK_FIX = 4,       // Real-Time Kinematic fix
    GPS_RTK_FLOAT = 5      // RTK float solution
} gps_fix_quality_t;

Data Structure

typedef struct {
    // Position Data
    double latitude;           // ±90 degrees (North/South)
    double longitude;          // ±180 degrees (East/West)
    float altitude;            // Meters above sea level
    
    // Velocity & Direction
    float speed;               // Meters per second
    float heading;             // 0-360 degrees (course over ground)
    
    // Accuracy Indicators
    float hdop;                // Horizontal dilution of precision
    float vdop;                // Vertical dilution of precision
    int32_t satellites;        // Number of satellites in view
    gps_fix_quality_t fix_quality;
    
    // Timestamps
    int64_t utc_timestamp;     // Unix epoch (milliseconds)
    uint32_t timestamp;        // System timestamp (last reading)
    uint32_t last_timestamp;   // System timestamp (previous reading)
    
    // Status
    bool is_valid;             // Data validity flag
    
    // UART Parsing State
    char rx_buffer[256];       // UART receive buffer
    uint16_t rx_index;         // Current buffer position
    bool sentence_ready;       // Complete sentence available
} gps_data_t;

NMEA Sentences Supported

Initialization & Usage

Initialize GPS

gps_data_t gps_data;
gps_sensor_init(&gps_data);

Poll GPS Data

result_t gps_poll_result = poll_gps_sensor(&gps_data);

if (gps_poll_result == RESULT_OK) {
    double latitude = gps_data.latitude;
    double longitude = gps_data.longitude;
    float altitude = gps_data.altitude;
    int32_t satellites = gps_data.satellites;
    float hdop = gps_data.hdop;
}

Validation Functions

// Validate latitude (-90 to +90)
result_t validate_gps_latitude(double latitude);

// Validate longitude (-180 to +180)
result_t validate_gps_longitude(double longitude);

// Validate HDOP (horizontal dilution of precision)
// Typical range: 0-50
result_t validate_gps_hdop(float hdop);

// Validate satellite count
// Typical: 0-30 satellites
result_t validate_gps_satellite_count(int32_t satellites);

Protobuf Message Format

message SensorBoardGPSInfo {
    double latitude;
    double longitude;
    float altitude;
    float speed;
    float heading;
    float hdop;
    float vdop;
    int32 satellites;
    SensorState state;
    GPSErrorCode error_code;
}

Error Handling

if (gps_poll_result == RESULT_ERR_UNIMPLEMENTED) {
    // Hardware not connected
    diagnostics.gps_sensor_1.state = SensorState_SENSOR_IDLE;
    diagnostics.gps_sensor_1.error_code = GPSErrorCode_GPS_COMMUNICATION_FAILURE;
} else if (gps_poll_result == RESULT_ERR_COMMS) {
    // Communication error (timeout/CRC)
    diagnostics.gps_sensor_1.state = SensorState_SENSOR_ERROR;
} else if (gps_poll_result == RESULT_OK) {
    // Validate data before accepting
    if (validate_gps_latitude(gps_data.latitude) == RESULT_OK) {
        diagnostics.gps_sensor_1.state = SensorState_SENSOR_OPERATING;
    }
}

Integration Notes

• Configured for dual GPS redundancy capability
• UART buffer size: 256 bytes
• NMEA sentence max length: 83 characters
• Data published to network at main loop interval (5 seconds default)
• All GPS data transmitted via UDP with Protobuf encoding
• Temperature range: -40°C to +85°C (standard)