ArduPilot开源飞控之AP_Baro_ExternalAHRS

1. 源由

鉴于ArduPilot开源飞控之AP_Baro中涉及Sensor Driver有以下总线类型：

1. I2C
2. Serial UART
3. CAN
4. SITL //模拟传感器(暂时并列放在这里)

ArduPilot之开源代码Sensor Drivers设计的front-end / back-end分层设计思路，AP_Baro主要描述的是front-end。

为了更好的从整体理解气压计这个传感器的嵌入式应用，这里深入到back-end驱动层，针对基于串行协议的气压计设备，进行一个研读和理解。

2. back-end抽象类

AP_Baro_Backend驱动层需实现方法：

• void update()
• static AP_Baro_Backend *probe(AP_Baro &baro, AP_HAL::OwnPtr dev)

注：通常来说使用ChibiOS的都有定时器，如果没有定时器，可以使用void accumulate(void)来实现传感器的数据定时获取。

class AP_Baro_Backend
{
public:
    AP_Baro_Backend(AP_Baro &baro)
    virtual ~AP_Baro_Backend(void) {}

    // each driver must provide an update method to copy accumulated
    // data to the frontend
    virtual void update() = 0

    // accumulate function. This is used for backends that don't use a
    // timer, and need to be called regularly by the main code to
    // trigger them to read the sensor
    virtual void accumulate(void) {}

    void backend_update(uint8_t instance)

    //  Check that the baro valid by using a mean filter.
    // If the value further that filtrer_range from mean value, it is rejected.
    bool pressure_ok(float press)
    uint32_t get_error_count() const { return _error_count }

#if AP_BARO_MSP_ENABLED
    virtual void handle_msp(const MSP::msp_baro_data_message_t &pkt) {}
#endif

#if AP_BARO_EXTERNALAHRS_ENABLED
    virtual void handle_external(const AP_ExternalAHRS::baro_data_message_t &pkt) {}
#endif

    /*
      device driver IDs. These are used to fill in the devtype field
      of the device ID, which shows up as BARO_DEVID* parameters to
      users.
     */
    enum DevTypes {
        DEVTYPE_BARO_SITL     = 0x01,
        DEVTYPE_BARO_BMP085   = 0x02,
        DEVTYPE_BARO_BMP280   = 0x03,
        DEVTYPE_BARO_BMP388   = 0x04,
        DEVTYPE_BARO_DPS280   = 0x05,
        DEVTYPE_BARO_DPS310   = 0x06,
        DEVTYPE_BARO_FBM320   = 0x07,
        DEVTYPE_BARO_ICM20789 = 0x08,
        DEVTYPE_BARO_KELLERLD = 0x09,
        DEVTYPE_BARO_LPS2XH   = 0x0A,
        DEVTYPE_BARO_MS5611   = 0x0B,
        DEVTYPE_BARO_SPL06    = 0x0C,
        DEVTYPE_BARO_UAVCAN   = 0x0D,
        DEVTYPE_BARO_MSP      = 0x0E,
        DEVTYPE_BARO_ICP101XX = 0x0F,
        DEVTYPE_BARO_ICP201XX = 0x10,
        DEVTYPE_BARO_MS5607   = 0x11,
        DEVTYPE_BARO_MS5837   = 0x12,
        DEVTYPE_BARO_MS5637   = 0x13,
        DEVTYPE_BARO_BMP390   = 0x14,
    }
    
protected:
    // reference to frontend object
    AP_Baro &_frontend

    void _copy_to_frontend(uint8_t instance, float pressure, float temperature)

    // semaphore for access to shared frontend data
    HAL_Semaphore _sem

    virtual void update_healthy_flag(uint8_t instance)

    // mean pressure for range filter
    float _mean_pressure 
    // number of dropped samples. Not used for now, but can be usable to choose more reliable sensor
    uint32_t _error_count

    // set bus ID of this instance, for BARO_DEVID parameters
    void set_bus_id(uint8_t instance, uint32_t id) {
        _frontend.sensors[instance].bus_id.set(int32_t(id))
    }
}
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3. 方法实现

由于气压数据来自串行总线，因此，其逻辑与MSP、CAN协议类似，相对简单，没有校准等复杂物理公式。

3.1 AP_Baro_ExternalAHRS

实例初始化。

AP_Baro_ExternalAHRS::AP_Baro_ExternalAHRS
 ├──> instance = _frontend.register_sensor()
 └──> set_bus_id(instance, AP_HAL::Device::make_bus_id(AP_HAL::Device::BUS_TYPE_SERIAL,port,0,0))
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3.2 update

front-end / back-end数据更新。

AP_Baro_ExternalAHRS::update
 └──> 
     ├──> WITH_SEMAPHORE(_sem)
     ├──> _copy_to_frontend(instance, sum_pressure/count, sum_temp/count)
     ├──> sum_pressure = sum_temp = 0
     └──> count = 0
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3.3 handle_external

处理串行协议中气压和温度数据。

AP_Baro_ExternalAHRS::handle_external
 ├──> 
 │   └──> return // not for us
 ├──> WITH_SEMAPHORE(_sem)
 ├──> sum_pressure += pkt.pressure_pa
 ├──> sum_temp += pkt.temperature
 └──> count++
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3.4 Serial port

串行口驱动数据接收。

AP_Vehicle::setup
 └──> AP_ExternalAHRS::init
     └──> AP_ExternalAHRS_VectorNav::AP_ExternalAHRS_VectorNav
         └──> AP_ExternalAHRS_VectorNav::update_thread  //thread_create
             └──> AP_ExternalAHRS_VectorNav::check_uart
                 ├──> AP_ExternalAHRS_VectorNav::process_packet1
                 │   └──> AP_Baro::handle_external
                 │       └──> AP_Baro_ExternalAHRS::handle_external
                 └──> AP_ExternalAHRS_VectorNav::process_packet_VN_100
                     └──> AP_Baro::handle_external
                         └──> AP_Baro_ExternalAHRS::handle_external
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4. 参考资料

【1】ArduPilot开源飞控系统之简单介绍
【2】ArduPilot之开源代码Task介绍
【3】ArduPilot飞控启动&运行过程简介
【4】ArduPilot之开源代码Library&Sketches设计
【5】ArduPilot之开源代码Sensor Drivers设计