C++ Boost::asio 与 Arduino 的串行通信无法写入

Question

I tried to communicate with my Arduino Uno using the Boost Asio library. Somehow I can't send data to my Arduino, and I have no idea what i'm doing wrong. Reading works fine, but writing only works when i open a terminal and say:

cat /dev/ttyACM0

When this terminal window is open, and I run my C++ application it works otherwise it doesn't work.

Code of the test application (C++):

#include <iostream>
#include <boost/asio.hpp>

char* message;

int main()
{

    boost::asio::io_service ioservice;
    boost::asio::serial_port serial(ioservice, "/dev/ttyACM0");

    serial.set_option(boost::asio::serial_port_base::baud_rate(115200));
    serial.set_option(boost::asio::serial_port::flow_control(boost::asio::serial_port::flow_control::none));
    serial.set_option(boost::asio::serial_port::parity(boost::asio::serial_port::parity::none));
    serial.set_option(boost::asio::serial_port::stop_bits(boost::asio::serial_port::stop_bits::one));
    serial.set_option(boost::asio::serial_port::character_size(boost::asio::serial_port::character_size(8)));

    std::string s = "u";
    boost::asio::streambuf b;
    std::ostream os(&b);
    os << s;
    boost::asio::write(serial, b.data());

    if (serial.is_open()) {
        serial.close();
    }

    return 0;
}

Code of my Arduino application:

#include "Servo.h"

Servo servo;
void setup() {
  Serial.begin(115200);
  servo.attach(9);
  servo.write(0);
}

void loop() {
  if(Serial.available()) {
    char c = Serial.read();
    if(c == 'u') {
      servo.write(180);
    } else if (c == 'v') {
      servo.write(0);
    }
  }
}

I tried this both on my Ubuntu 18.04 and Debian 10 installation to rule out a permission issue, so I think there is something wrong with my code.

Update:

I found the issue, the Arduino is restarting when making a serial connection. When I add a thread sleep for for example 5 seconds and after that resent the data it works (because then it keeps the serial connection alive). I'm still looking for a permanent solution, so that I don't have to do a write before I really want to write something.

Update 2:

Apparently I don't even have to do a write, but where must be a small delay before I can start writing, because when after opening the port the Arduino is still restarting.

Answer 1

I fixed it with adding a small delay before writing to the serial port. As I also wrote in my comment above, the Arduino is restarting when you start a serial communication.

This can be disabled on several ways: https://playground.arduino.cc/Main/DisablingAutoResetOnSerialConnection/

Another option is to send a "ready" signal from the Arduino to know in your application that the Arduino is rebooted. So then start in your application with reading, and when you received that message, you can start writing.