beast_input_serial.h

// -*- c++ -*-

// Copyright (c) 2015-2016, FlightAware LLC.
// Copyright (c) 2015, Oliver Jowett <oliver@mutability.co.uk>
// All rights reserved.

// Redistribution and use in source and binary forms, with or without
// modification, are permitted provided that the following conditions are met:

// * Redistributions of source code must retain the above copyright notice, this
//   list of conditions and the following disclaimer.

// * Redistributions in binary form must reproduce the above copyright notice,
//   this list of conditions and the following disclaimer in the documentation
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#ifndef BEAST_INPUT_SERIAL_H
#define BEAST_INPUT_SERIAL_H

#include <boost/asio/serial_port.hpp>

#include "beast_input.h"

namespace beast {
    class SerialInput : public BeastInput {
      public:
        typedef std::shared_ptr<SerialInput> pointer;

        // the standard baud rates to try, in their preferred order
        const std::array<unsigned int, 2> autobaud_standard_rates{{3000000, 1000000}};

        // the initial interval to wait for sufficient good messages (see autobaud_good_messages) before changing baud rates
        const std::chrono::milliseconds autobaud_base_interval = std::chrono::milliseconds(1000);

        // the maximum interval between changing baud rates
        const std::chrono::milliseconds autobaud_max_interval = std::chrono::milliseconds(16000);

        // the number of consecutive messages without sync errors needed before the baud rate is fixed
        const unsigned int autobaud_good_messages = 4;

        // the number of bytes without good sync before restarting autobauding
        const unsigned int autobaud_restart_bytes = 1000;

        // the number of bytes to try to read at a time from the connection
        const size_t read_buffer_size = 4096;

        // how long to wait between scheduling reads (to reduce the spinning on short messages)
        const std::chrono::milliseconds read_interval = std::chrono::milliseconds(50);

        // factory method
        static pointer create(boost::asio::io_service &service, const std::string &path, unsigned int fixed_baud_rate = 0, const Settings &fixed_settings = Settings(), const modes::Filter &filter = modes::Filter()) { return pointer(new SerialInput(service, path, fixed_baud_rate, fixed_settings, filter)); }

      protected:
        std::string what() const override;
        void try_to_connect(void) override;
        void disconnect(void) override;
        bool low_level_write(std::shared_ptr<helpers::bytebuf> message) override;
        void saw_good_message(void) override;
        bool can_dispatch(void) const override;
        void apply_connection_settings(Settings &settings) override;

      private:
        // construct a new serial input instance, don't start yet
        SerialInput(boost::asio::io_service &service_, const std::string &path_, unsigned int fixed_baud_rate, const Settings &fixed_settings_, const modes::Filter &filter_);

        void start_reading(const boost::system::error_code &ec = boost::system::error_code());
        void advance_autobaud(void);
        void handle_error(const boost::system::error_code &ec);
        void check_framing_errors(void);

        // path to the serial device
        std::string path;

        // the port we're using
        boost::asio::serial_port port;

        // true if we are actively hunting for the correct baud rate
        bool autobauding;

        // vector of baud rates to try, single entry if a fixed rate is set
        std::vector<unsigned int> autobaud_rates;

        // current iterator into autobaud_rates
        std::vector<unsigned int>::iterator autobaud_rate;

        // actual rate in use
        unsigned int baud_rate;

        // how long to wait between autobaud attempts; doubles (up to a limit)
        // each time all rates in autobaud_rates have been tried
        std::chrono::milliseconds autobaud_interval;

        // timer that expires after autobaud_interval
        boost::asio::steady_timer autobaud_timer;

        // timer that expires when we want to read some more data
        boost::asio::steady_timer read_timer;

        // cached buffer used for reads
        std::shared_ptr<helpers::bytebuf> readbuf;

        // have we warned about a possibly bad baud rate?
        bool warned_about_rate;
    };
}; // namespace beast

#endif