ardupilot/libraries/AP_Airspeed/AP_Airspeed_NMEA.h

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#pragma once
#include <AP_HAL/AP_HAL_Boards.h>
// note additional vehicle restrictions are made in the .cpp file!
#ifndef AP_AIRSPEED_NMEA_ENABLED
#define AP_AIRSPEED_NMEA_ENABLED AP_AIRSPEED_BACKEND_DEFAULT_ENABLED
#endif
#if AP_AIRSPEED_NMEA_ENABLED
#include "AP_Airspeed_Backend.h"
#include <AP_HAL/AP_HAL.h>
class AP_Airspeed_NMEA : public AP_Airspeed_Backend
{
public:
AP_Airspeed_NMEA(AP_Airspeed &frontend, uint8_t _instance);
// probe and initialise the sensor
bool init(void) override;
// this reads airspeed directly
bool has_airspeed() override {return true;}
// read the from the sensor
bool get_airspeed(float &airspeed) override;
// return the current temperature in degrees C
bool get_temperature(float &temperature) override;
private:
// pointer to serial uart
AP_HAL::UARTDriver *_uart = nullptr;
// add a single character to the buffer and attempt to decode
// returns true if a complete sentence was successfully decoded
// distance should be pulled directly from _distance_m member
bool decode(char c);
// decode the just-completed term
// returns true if new sentence has just passed checksum test and is validated
bool decode_latest_term();
// enum for handled messages
enum sentence_types : uint8_t {
TPYE_MTW = 0,
TYPE_VHW,
};
// message decoding related members
char _term[15]; // buffer for the current term within the current sentence
uint8_t _term_offset; // offset within the _term buffer where the next character should be placed
uint8_t _term_number; // term index within the current sentence
float _speed; // speed in m/s
float _temp; // temp in deg c
uint8_t _checksum; // checksum accumulator
bool _term_is_checksum; // current term is the checksum
bool _sentence_done; // has the current term already been decoded
bool _sentence_valid; // is the decodeing valid so far
sentence_types _sentence_type; // the sentence type currently being processed
// Store the temp ready for a temp request
float _temp_sum;
uint16_t _temp_count;
// store last sent speed and temp as update rate is slow
float _last_temp;
float _last_speed;
// time last message was received
uint32_t _last_update_ms;
};
#endif // AP_AIRSPEED_NMEA_ENABLED