ardupilot/libraries/AP_HAL_Linux/UARTDriver.h

#pragma once

#include "AP_HAL_Linux.h"

#include "SerialDevice.h"

class Linux::UARTDriver : public AP_HAL::UARTDriver {
public:
    UARTDriver(bool default_console);

    static UARTDriver *from(AP_HAL::UARTDriver *uart) {
        return static_cast<UARTDriver*>(uart);
    }

    /* Linux implementations of UARTDriver virtual methods */
    void begin(uint32_t b);
    void begin(uint32_t b, uint16_t rxS, uint16_t txS);
    void end();
    void flush();
    bool is_initialized();
    void set_blocking_writes(bool blocking);
    bool tx_pending();

    /* Linux implementations of Stream virtual methods */
    int16_t available();
    int16_t txspace();
    int16_t read();

    /* Linux implementations of Print virtual methods */
    size_t write(uint8_t c);
    size_t write(const uint8_t *buffer, size_t size);

    void set_device_path(const char *path);

    bool _write_pending_bytes(void);
    virtual void _timer_tick(void);

    enum flow_control get_flow_control(void) { return _flow_control; }

private:
    SerialDevice *_device = nullptr;
    bool _nonblocking_writes;
    bool _console;
    volatile bool _in_timer;
    uint16_t _base_port;
    char *_ip;
    char *_flag;
    bool _connected; // true if a client has connected         
    bool _packetise; // true if writes should try to be on mavlink boundaries
    enum flow_control _flow_control;

    void _allocate_buffers(uint16_t rxS, uint16_t txS);
    void _deallocate_buffers();
    void _udp_start_connection(void);
    void _tcp_start_connection(void);
    bool _serial_start_connection(void);
    bool _qflight_start_connection(void);

    enum device_type {
        DEVICE_TCP,
        DEVICE_UDP,
        DEVICE_SERIAL,
#if CONFIG_HAL_BOARD_SUBTYPE == HAL_BOARD_SUBTYPE_LINUX_QFLIGHT
        DEVICE_QFLIGHT,
#endif
        DEVICE_UNKNOWN
    };

    enum device_type _parseDevicePath(const char *arg);
    uint64_t _last_write_time;    

protected:
    const char *device_path;
    volatile bool _initialised;
    // we use in-task ring buffers to reduce the system call cost
    // of ::read() and ::write() in the main loop
    uint8_t *_readbuf;
    uint16_t _readbuf_size;

    // _head is where the next available data is. _tail is where new
    // data is put
    volatile uint16_t _readbuf_head;
    volatile uint16_t _readbuf_tail;

    uint8_t *_writebuf;
    uint16_t _writebuf_size;
    volatile uint16_t _writebuf_head;
    volatile uint16_t _writebuf_tail;

    virtual int _write_fd(const uint8_t *buf, uint16_t n);
    virtual int _read_fd(uint8_t *buf, uint16_t n);

};