c++ - 通过 RS232 串行端口从条码扫描器读取异步数据

Question

我有一个条形码阅读器，它通过 RS232 串行端口连接到 PC。我正在编写一个 C++ 代码来向条形码扫描器发送命令并将响应返回给 PC。目前程序可以正确发送数据到设备，但无法读取条码扫描器的响应。在这种情况下，一旦我们向条形码阅读器发送命令，它就会以肯定或否定的确认回应。

e.g:- Send BEEP command.
 1. Host(PC) send a BEEP command to barcode scanner
 2. Barcode scanner make a beep sound and send the acknowledgement back
    to host (PC)
 3. Host (PC) read the acknowledgement

在下面的代码中，前两步工作正常，但我无法正确编写第三步。请有人帮助我更正我的源代码以异步读取条码扫描器的响应。

主要.cpp

#include <iostream>
extern "C"
{
    #include <stdlib.h>
    #include <stdio.h>
    #include <unistd.h>
}
#include "DeviceRS232.h"
#include "Message.h"


int main()
{
    unsigned char recvBuffer[257];
    unsigned char ledOn[] = {0x05, 0xE7, 0x04, 0x00, 0x0D, 0x00};
    unsigned char SSIBuffer[] = {0x00, 0xC6, 0x04, 0x08, 0x11, 0xEE, 0x01};
    unsigned char requestRevision[] = {0x00, 0x04, 0xA3, 0x04, 0x00};
    unsigned char sendBeep[] = {0x00, 0xE6, 0x04, 0x00, 0x05};

    Message beepCommand(sendBeep, sizeof(sendBeep)/sizeof(sendBeep[0]));

    std::cout << "*********************************************************" << std::endl << std::endl;
    DeviceRS232 dev_rs232;
    dev_rs232.setDefaultAttributes();
    dev_rs232.openSerialPort();


    // Send BEEP command several times.
    std::cout << "---Start sending beep---" << std::endl;
    for(int x=0; x<1; x++)
    {
        int sizeSent = dev_rs232.sendDataBuffer(beepCommand.getCommandData(), beepCommand.getLen());
        if( sizeSent > 0)
        {
            std::cout << "Data sent: " <<  sizeSent << std::endl;
        }

        memset(recvBuffer, 0, sizeof(recvBuffer));
        int recvSize = dev_rs232.receiveDataBuffer(recvBuffer, sizeof(recvBuffer));
        std::cout << "Date Received, Data: " <<  recvBuffer << " Size: " << recvSize << std::endl;
        sleep(2);
        /**
        while(true)
        {
            memset(recvBuffer, 0, sizeof(recvBuffer));
            int recvSize = dev_rs232.receiveDataBuffer(recvBuffer, sizeof(recvBuffer));
            if(recvSize > 0)
                std::cout << "Date Received, Data: " <<  recvBuffer << " Size: " << recvSize << std::endl;
            sleep(2);
        }*/
    }
    std::cout << "---End sending beep-----\n" << std::endl;


    dev_rs232.closeSerialPort();
    std::cout << "*********************************************************" << std::endl;


    return 0;
}

消息.h

#ifndef MESSAGE_H
#define MESSAGE_H

#include <iostream>
#include <string>
#include <numeric>
extern "C"
{
    #include <stdlib.h>
    #include <stdio.h>
    #include <unistd.h>
}

class Message
{
    public:
        Message();              //  default constructor
        virtual ~Message();     //  destructor


        Message(const std::basic_string<unsigned char> msg) : commandMsg(msg)
        {
            printf("msg[0]:%x\n", msg[4]);
            std::cout << "length: " << commandMsg.length() << std::endl;

            //commandMsg[0] = commandMsg.length();
            appendChecksum();
        };

        Message(const unsigned char *msg, int msglen) : commandMsg(msg, msglen)
        {
            commandMsg[0] = commandMsg.length();
            appendChecksum();
        };

        const unsigned char *getCommandData() const
        {
            return commandMsg.c_str();
        }

        int getLen() const
        {
            return commandMsg.length();
        }


    protected:
    private:
        int appendChecksum();
        std::basic_string<unsigned char> commandMsg;
};

#endif // MESSAGE_H

消息.cpp

#include "Message.h"

Message::Message()
{
    //ctor
}

Message::~Message()
{
    //dtor
}

int Message::appendChecksum()
{
    int sum = -std::accumulate(commandMsg.begin(), commandMsg.end(), 0);

    commandMsg.push_back(0xFF & (sum >> 8));
    commandMsg.push_back(0xFF & sum);
}

设备RS232.h

#ifndef DEVICERS232_H
#define DEVICERS232_H

extern "C"
{
#include <stdio.h>
#include <string.h>
#include <termios.h>
#include <sys/ioctl.h>
#include <unistd.h>
#include <fcntl.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <limits.h>
#include <stdlib.h>
}

#include <string>

#define MAX_SERIAL_PORT_NO  30



class DeviceRS232
{
    public:
        DeviceRS232();
        virtual ~DeviceRS232();

        int fdRS232;                    //  file descriptor for the serial port

        void setSerialPort(std::string sp);
        void setBaudRate(long baud);
        void setDataBits(int dataBit);
        void setStopBits(int stopBit);
        void setNumberOfParityBits(int nparityBits);
        void setDefaultAttributes();
        long getBaudRate();
        std::string getSerialPort();
        int openSerialPort();
        int readUserConfiguration();
        int sendDataBuffer(const unsigned char *dataBuffer, size_t bufferSize);
        int receiveDataBuffer(unsigned char *dataBuffer, size_t bufferSize);
        void closeSerialPort();


    protected:
        std::string serialPort;         //  Serial port like /dev/ttyS0
        long baudRate;                  //  Scanner baud rate
        int dataBits;                   //  data bits
        int stopBits;                   //  stop bits
        int numberOfParityBits;         //  number of parity bits
        termios oldSerialPortSetting;   //  Current values of termios structure for /dev/ttyS0
        termios newSerialPortSetting;   //  new termios attributes for /dev/ttyS0


    private:
};

#endif // DEVICERS232_H

设备RS232.cpp

#include "DeviceRS232.h"

DeviceRS232::DeviceRS232()
{
    //ctor
}

DeviceRS232::~DeviceRS232()
{
    //dtor
}

void DeviceRS232::setSerialPort(std::string sp)
{
    serialPort = sp;
}

void DeviceRS232::setBaudRate(long baud)
{
    baudRate = baud;
}

void DeviceRS232::setDataBits(int dataBit)
{
    dataBits = dataBit;
}

void DeviceRS232::setStopBits(int stopBit)
{
    stopBits = stopBit;
}

void DeviceRS232::setNumberOfParityBits(int nparityBits)
{
    numberOfParityBits = nparityBits;
}

void DeviceRS232::setDefaultAttributes()
{
    std::string sp = "/dev/ttyS0";
    long baud = 9600;
    int dataBit = 1;
    int stopBit = 1;
    int nparityBits = 0;

    setSerialPort(sp);
    setBaudRate(baud);
    setDataBits(dataBit);
    setStopBits(stopBit);
    setNumberOfParityBits(nparityBits);
}

long DeviceRS232::getBaudRate()
{
    return baudRate;
}

std::string DeviceRS232::getSerialPort()
{
    return serialPort;
}

int DeviceRS232::openSerialPort()
{
    int fd, baudr, status, portStatus;
    setDefaultAttributes();

    switch(getBaudRate())
    {
        case      50 : baudr = B50;
                       break;
        case      75 : baudr = B75;
                       break;
        case     110 : baudr = B110;
                       break;
        case     134 : baudr = B134;
                       break;
        case     150 : baudr = B150;
                       break;
        case     200 : baudr = B200;
                       break;
        case     300 : baudr = B300;
                       break;
        case     600 : baudr = B600;
                       break;
        case    1200 : baudr = B1200;
                       break;
        case    1800 : baudr = B1800;
                       break;
        case    2400 : baudr = B2400;
                       break;
        case    4800 : baudr = B4800;
                       break;
        case    9600 : baudr = B9600;
                       break;
        case   19200 : baudr = B19200;
                       break;
        case   38400 : baudr = B38400;
                       break;
        case   57600 : baudr = B57600;
                       break;
        case  115200 : baudr = B115200;
                       break;
        case  230400 : baudr = B230400;
                       break;
        case  460800 : baudr = B460800;
                       break;
        case  500000 : baudr = B500000;
                       break;
        case  576000 : baudr = B576000;
                       break;
        case  921600 : baudr = B921600;
                       break;
        case 1000000 : baudr = B1000000;
                       break;
        default      : printf("invalid baudrate\n");
                       return(1);
                       break;
    }

    //  Open serial port
    fd = open(getSerialPort().c_str(),  O_RDWR | O_NOCTTY | O_NDELAY);
    if(fd == -1)
    {
        printf("Unable to open serial port...\n");
        perror(getSerialPort().c_str());
        return 1;
    }

    fdRS232 = fd;

    fcntl(fdRS232, F_SETFL, FNDELAY);
    status = tcgetattr(fdRS232, &oldSerialPortSetting);
    if(status == -1)
    {
        close(fdRS232);
        printf("Unable to get serial port attributes...\n");
        return 1;
    }

    memset(&newSerialPortSetting, 0, sizeof(newSerialPortSetting));
    newSerialPortSetting.c_cflag = baudr | CS8 | CLOCAL | CREAD; //
    newSerialPortSetting.c_iflag = IGNPAR;
    newSerialPortSetting.c_oflag = 0;
    newSerialPortSetting.c_lflag = 0;
    newSerialPortSetting.c_cc[VMIN] = 0;
    newSerialPortSetting.c_cc[VTIME] = 0;

    status = tcsetattr(fdRS232, TCSANOW, &newSerialPortSetting);
    if(status==-1)
    {
        close(fdRS232);
        perror("unable to adjust portsettings ");
        return 1;
    }

    //  Get the status of opened serial port
    if(ioctl(fdRS232, TIOCMGET, &portStatus) == -1)
    {
        perror("Unable to get port status");
        return 1;
    }

    //  Tern on DTR and RTS
    portStatus |= TIOCM_DTR;
    portStatus |= TIOCM_RTS;

    //  Set the status of the port with new DTR, RTS values
    if(ioctl(fdRS232, TIOCMSET, &portStatus) == -1)
    {
        perror("Unable to set port status...");
        return 1;
    }

  return 0;
}

int DeviceRS232::sendDataBuffer(const unsigned char *dataBuffer, size_t bufferSize)
{
    return write(fdRS232, dataBuffer, bufferSize);
}

int DeviceRS232::receiveDataBuffer(unsigned char *dataBuffer, size_t bufferSize)
{
    /**int recvSize = 0;
    recvSize = read(fdRS232, dataBuffer, bufferSize);
    return recvSize;*/

    unsigned char recvBuffer[255];
    unsigned char *ptrChar;
    int nBytes;

    ptrChar = recvBuffer;
    memset(recvBuffer, 0x00, sizeof(recvBuffer));
    while((nBytes = read(fdRS232, ptrChar, recvBuffer+sizeof(recvBuffer) - ptrChar -1)) > 0)
    {
        ptrChar += nBytes;
        //printf("while - %d\n", nBytes);
    }

    //printf("recvBuffer : %x\n", recvBuffer[0]);
    //printf("recvBuffer : %x\n", recvBuffer[1]);
    //printf("recvBuffer : %x\n", recvBuffer[2]);
    //printf("recvBuffer : %x\n", recvBuffer[3]);
    //printf("recvBuffer : %x\n", recvBuffer[4]);
    dataBuffer = recvBuffer;

    return nBytes;
}

void DeviceRS232::closeSerialPort()
{
    int portStatus;

    if(ioctl(fdRS232, TIOCMGET, &portStatus) == -1)
    {
        perror("Unable to get the port status");
    }

    //  Tern off DTR and RTS
    portStatus &= ~TIOCM_DTR;
    portStatus &= ~TIOCM_RTS;

    //  Set the status of the port with new DTR, RTS values
    if(ioctl(fdRS232, TIOCMSET, &portStatus) == -1)
    {
        perror("Unable to set port status...");
    }

    close(fdRS232);
}

我的错误方法是 int DeviceRS232::receiveDataBuffer(unsigned char *dataBuffer, size_t bufferSize)

控制台输出如下:

*********************************************************

---Start sending beep---
Data sent: 7
Date Received, Data:  Size: 0
---End sending beep-----

*********************************************************

Process returned 0 (0x0)   execution time : 2.004 s
Press ENTER to continue.

Answer 1

正如其他人所指出的，一个可疑区域是您发送的字节数。条形码阅读器并不总是发送 257 个字节，而是可能只需要命令中的字节数，而不是更多。

此外，您的代码有许多重复操作，用于计算消息末尾的校验和。这表明类将有助于简化设计。那么，这里是一个 Message为此类:

#include <vector>
#include <numeric>
#include <string>

class Message 
{
public:
    Message(const std::basic_string<unsigned char> msg) : mymsg(msg) { 
        mymsg[0] = mymsg.length(); appendChecksum(); };
    Message(const unsigned char *msg, int msglen) : mymsg(msg, msglen) { 
        mymsg[0] = mymsg.length(); appendChecksum(); };
    const unsigned char *getData() const { return mymsg.c_str(); }
    size_t getLen() const { return mymsg.length(); }

private:
        int appendChecksum();
        std::basic_string<unsigned char> mymsg;
};


int Message::appendChecksum()
{
    int sum = -std::accumulate(mymsg.begin(), mymsg.end(), 0);
    mymsg.push_back(0xff & (sum >> 8));
    mymsg.push_back(0xff & sum);
    return sum;
}

现在在您的 main 中例程，您可以删除几十行代码并改用这些代码(如果您使用的是 C++11):

    Message setparams{{0x00, 0xc6, 0x04, 0x08, 0x11, 0xee, 0x01}};
    Message beep{{0x00, 0xe6, 0x04, 0x00, 0x05}};
    Message getrevision{{0x00, 0xA3, 0x04, 0x00}};
    Message ledOn{{0x00, 0xe7, 0x04, 0x00, 0x0d, 0x00}};

如果您不使用 C++11(这太可惜了!)，您可以改用这种不太干净的样式:

unsigned char parms[] = {0x00, 0xc6, 0x04, 0x08, 0x11, 0xee, 0x01};
Message setparams(parms,sizeof(parms)/sizeof(parms[0]));

请注意，第一个字节设置为零而不是长度。这样做是因为构造函数会在计算和附加校验和之前自动计算并在该字节中设置适当的长度。当然，还有其他方法可以做到这一点，但我会把它留给你。

最后，在你的循环中，你现在可以使用这一行:

int sizeSent = dev_rs232.sendDataBuffer(beep.getData(), beep.getLen());

这可能会或可能不会真正解决问题，但它会帮助您从一个更干净的程序开始。

此外，还有一些风格和设计建议:

1. 改掉 using namespace std 的习惯
2. 使用iostream而不是 printf
3. 不必再调用setDefaultAttributes()创 build 备后，立即让构造函数设置合理的默认值
4. 消除接收缓冲区大小的“魔数(Magic Number)”，例如 4096。相反，使用命名为 static const .这将使程序更易于理解和维护。
5. 考虑使用现有的库，例如 boost::asio而不是自己滚动

祝你好运!

编辑:根据您敏锐(且正确!)的观察，Message当输入普通 unsigned char * 时，构造函数无法正常工作，我添加了第二个构造函数并修改了非 C++11 版本的代码。对于给您带来的不便，我们深表歉意，感谢您让我诚实。