ardupilot/libraries/AP_GPS/GPS_Backend.h

/*
   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, see <http://www.gnu.org/licenses/>.
 */

/*
  GPS driver backend class
 */
#pragma once

#include <GCS_MAVLink/GCS_MAVLink.h>
#include <AP_RTC/JitterCorrection.h>
#include "AP_GPS.h"

class AP_GPS_Backend
{
public:
    AP_GPS_Backend(AP_GPS &_gps, AP_GPS::GPS_State &_state, AP_HAL::UARTDriver *_port);

    // we declare a virtual destructor so that GPS drivers can
    // override with a custom destructor if need be.
    virtual ~AP_GPS_Backend(void) {}

    // The read() method is the only one needed in each driver. It
    // should return true when the backend has successfully received a
    // valid packet from the GPS.
    virtual bool read() = 0;

    // Highest status supported by this GPS. 
    // Allows external system to identify type of receiver connected.
    virtual AP_GPS::GPS_Status highest_supported_status(void) { return AP_GPS::GPS_OK_FIX_3D; }

    virtual bool is_configured(void) const { return true; }

    virtual void inject_data(const uint8_t *data, uint16_t len);

    //MAVLink methods
    virtual bool supports_mavlink_gps_rtk_message() const { return false; }
    virtual void send_mavlink_gps_rtk(mavlink_channel_t chan);

    virtual void broadcast_configuration_failure_reason(void) const { return ; }

    virtual void handle_msg(const mavlink_message_t &msg) { return ; }
#if HAL_MSP_GPS_ENABLED
    virtual void handle_msp(const MSP::msp_gps_data_message_t &pkt) { return; }
#endif
#if HAL_EXTERNAL_AHRS_ENABLED
    virtual void handle_external(const AP_ExternalAHRS::gps_data_message_t &pkt) { return; }
#endif
    
    // driver specific lag, returns true if the driver is confident in the provided lag
    virtual bool get_lag(float &lag) const { lag = 0.2f; return true; }

    // driver specific health, returns true if the driver is healthy
    virtual bool is_healthy(void) const { return true; }
    // returns true if the GPS is doing any logging it is expected to
    virtual bool logging_healthy(void) const { return true; }

    virtual const char *name() const = 0;

    void broadcast_gps_type() const;
    virtual void Write_AP_Logger_Log_Startup_messages() const;

    virtual bool prepare_for_arming(void) { return true; }

    // optional support for retrieving RTCMv3 data from a moving baseline base
    virtual bool get_RTCMV3(const uint8_t *&bytes, uint16_t &len) { return false; }
    virtual void clear_RTCMV3(void) {};

    virtual bool get_error_codes(uint32_t &error_codes) const { return false; }

    // return iTOW of last message, or zero if not supported
    uint32_t get_last_itow(void) const {
        return _last_itow;
    }

    enum DriverOptions : int16_t {
        UBX_MBUseUart2    = (1U << 0U),
        SBF_UseBaseForYaw = (1U << 1U),
        UBX_Use115200     = (1U << 2U),
        UAVCAN_MBUseDedicatedBus  = (1 << 3U),
    };

protected:
    AP_HAL::UARTDriver *port;           ///< UART we are attached to
    AP_GPS &gps;                        ///< access to frontend (for parameters)
    AP_GPS::GPS_State &state;           ///< public state for this instance

    // common utility functions
    int32_t swap_int32(int32_t v) const;
    int16_t swap_int16(int16_t v) const;

    /*
      fill in 3D velocity from 2D components
     */
    void fill_3d_velocity(void);

    /*
       fill in time_week_ms and time_week from BCD date and time components
       assumes MTK19 millisecond form of bcd_time
    */
    void make_gps_time(uint32_t bcd_date, uint32_t bcd_milliseconds);

    void _detection_message(char *buffer, uint8_t buflen) const;

    bool should_log() const;

    /*
      set a timestamp based on arrival time on uart at current byte,
      assuming the message started nbytes ago
     */
    void set_uart_timestamp(uint16_t nbytes);

    void check_new_itow(uint32_t itow, uint32_t msg_length);

    /*
      access to driver option bits
     */
    DriverOptions driver_options(void) const {
        return DriverOptions(gps._driver_options.get());
    }

#if GPS_MOVING_BASELINE
    bool calculate_moving_base_yaw(const float reported_heading_deg, const float reported_distance, const float reported_D);
    bool calculate_moving_base_yaw(AP_GPS::GPS_State &interim_state, const float reported_heading_deg, const float reported_distance, const float reported_D);
#endif //GPS_MOVING_BASELINE

    // get GPS type, for subtype config
    AP_GPS::GPS_Type get_type() const {
        return gps.get_type(state.instance);
    }

private:
    // itow from previous message
    uint32_t _last_itow;
    uint64_t _pseudo_itow;
    uint32_t _last_ms;
    uint32_t _rate_ms;
    uint32_t _last_rate_ms;
    uint16_t _rate_counter;

    JitterCorrection jitter_correction;
};