Question

我正试图在我的计算机和我的arduino之间建立一个串行通信通道。当我看到ArduinoIDE时，我从arduino发送了一个完美的消息 - 3个相同的数字。现在，我正在尝试创建一个c ++应用程序来在运行Ubuntu的计算机上读取该数据，但是我在字符串上得到了很多垃圾。我一直在阅读和搜索，但没有成功。任何人都可以帮我找到问题的根源吗？

代码：

SerialComm.h：

#ifndef SERIALCOMM_HPP
#define SERIALCOMM_HPP

#include <fstream>
#include <string>

#include <stdio.h> // standard input / output functions
#include <string.h> // string function definitions
#include <unistd.h> // UNIX standard function definitions
#include <fcntl.h> // File control definitions
#include <errno.h> // Error number definitions
#include <termios.h> // POSIX terminal control definitionss

class SerialComm {
public:

    SerialComm() noexcept {
    }

    virtual ~SerialComm() noexcept {
        tcsetattr(fd, TCSANOW, &port_settings);
        close(fd);
    }

    void begin(std::string port, speed_t baudrate);
    std::string read_data();

private:
    int fd;
    speed_t _baudrate;
    std::string _port;
    static constexpr int BUFFER_SIZE = 256;
    char buffer[BUFFER_SIZE];
    termios port_settings;
};

SerialComm.cpp

#include "SerialComm.hpp"

#include <iostream>

using namespace std;

void SerialComm::begin(string porta, speed_t baudrate) {
    _port = porta;
    _baudrate = baudrate;

    // abre a porta
    fd = open(_port.c_str(), O_RDWR | O_NOCTTY | O_NDELAY);

    if (fd == -1) {
        printf((string("Unable to open port ") + _port).c_str());
    } else {
        fcntl(fd, F_SETFL, 0);
        printf("port is open.\n");
    }

    cfsetispeed(&port_settings, _baudrate); // set baud rates
    cfsetospeed(&port_settings, _baudrate);

    port_settings.c_cflag &= ~PARENB; // set no parity, stop bits, data bits
    port_settings.c_cflag &= ~CSTOPB;
    port_settings.c_cflag &= ~CSIZE;
    port_settings.c_cflag |= CS8;

    tcsetattr(fd, TCSANOW, &port_settings); // apply the settings to the port   
}

string SerialComm::read_data() {
    int state = 1;

    while (true) {
        state = read(fd, buffer, BUFFER_SIZE);
        if (state > 0) 
        {
            return string( buffer );
        }
    }
}

main.ccp

int main(int argc, char* argv[])
{

    SerialComm serial;

    serial.begin("/dev/ttyACM0", B115200);

    for(auto i = 0; i < 100; ++i)
    {
        cout << serial.read_data() << endl;
    }
}

serial.ino：

double sinal = 0;

void setup()
{
  Serial.begin( 115200 );
}

void loop()
{
  sinal = analogRead( A0 ) * ( 5.0 / 1024.0 );
  Serial.print( "$" );
  Serial.print( sinal, 5 );
  Serial.print( "," );
  Serial.print( sinal, 5 );
  Serial.print( "," );
  Serial.print( sinal, 5 );
  Serial.print( "#\n" );
}

Arduino IDE输出：

$2.24121,2.24121,2.24121#
$2.24609,2.24609,2.24609#
$2.24121,2.24121,2.24121#
$2.24121,2.24121,2.24121#
$2.24609,2.24609,2.24609#

电脑输出：

$2.24609,2.24?�̯m#
$2.
09375#
$2.2412109375,2.2412109937500#
$2.2460937500,2.2460937500,2.2460937500#
375#
$2.2460937500,2.2460937500,2.2460937500#
$2.
375,2.2412109375#
$2.241210937937500#
$2.2460937500,2.2460937500,2.2460937500#

PS：以上是我能得到的最漂亮的输出。

Answer 1

除了未终止字符串缓冲区的问题之外，您也不能说只需一次调用read就会收到完整的消息。相反，你必须在循环中读取，直到你得到消息的结尾（你发送的换行符）。

这当然会给您带来另一个问题，即您可以在同一read次呼叫中收到一条消息的结尾和下一条消息的开头。这意味着您必须保存下一条消息的开头，并在下次调用read之前将其放入缓冲区。

Answer 2

我认为这是你的错误：

string SerialComm::read_data() {
    int state = 1;
    int receivedbyte = 0;  // never used!

    while (true) {
        state = read(fd, buffer, BUFFER_SIZE);
        if (state > 0) 
        {
            return string( buffer );
        }
    }
    buffer[receivedbyte + 1] = '\0';  // never reached!  And "off-by-one" if it were...
}

这可能会更好：

string SerialComm::read_data() {
    int receivedbyte = 0;

    while (true) {
        receivedbyte = read(fd, buffer, BUFFER_SIZE - 1);
        if (receivedbyte > 0) 
        {
            buffer[receivedbyte] = '\0';
            return string( buffer );
        }
    }
}

这应该消除由于未终止的字符串而导致的任何垃圾。也就是说，要获得漂亮的以换行符结尾的字符串，您可能需要一个外部循环来查找这些边界并以正确的方式划分流。

这样做的一种方法可能是：在类中声明string received以保存尚未返回给调用者的所有缓冲输入。然后，重写read_data（），如下所示：

string SerialComm::read_data()
{
    while (true)
    {
        size_t pos = received.find_first_of('\n', 0);
        if (pos != string::npos)
        {
            string result = received.substr(0, pos);
            received.erase(0, pos);
            return result;
        }

        int receivedbytes;
        do
        {
            receivedbytes = read(fd, buffer, BUFFER_SIZE - 1);
        } while (receivedbytes == 0);

        if (receivedbytes < 0)
            abort();  // error... you might want to handle it more cleanly, though

        buffer[receivedbytes] = 0;
        received += string( buffer );
    }
}

如果你想要一个没有完整行可以看到的空字符串的版本，而不是永远等待数据，你可以使用这个版本的代码。注意：如果缓存数据没有终止换行符，它将保留在它上面，直到它看到终止换行符。您可能希望添加单独的flush方法以使该数据可见。

string SerialComm::read_data()
{
    while (true)
    {
        size_t pos = received.find_first_of('\n', 0);
        if (pos != string::npos)
        {
            string result = received.substr(0, pos);
            received.erase(0, pos);
            return result;
        }

        int receivedbytes = read(fd, buffer, BUFFER_SIZE - 1);

        if (receivedbytes < 0)
            abort();  // error... you might want to handle it more cleanly, though

        if (receivedbytes == 0)
            return string();  // nothing to see yet

        // Add received data to buffer and loop to see if we have a newline yet.           
        buffer[receivedbytes] = 0;
        received += string( buffer );
    }
}

如何最大限度地减少arduino的串行通信读取错误

2 个答案: