如何修复 rs232 串口超时？答案

【问题标题】：How to fix timeout on rs232 serial port?如何修复 rs232 串口超时？
【发布时间】：2014-04-17 15:34:30
【问题描述】：

从串口读取时出现问题。问题在于，对于从rs232 端口读取的最后 2 个字节（CRC 字节），读取会一直等到timeval 中设置的超时结束，然后返回。在rs485 上，使用与读取相同的方法，读取返回正常。我在调试时看到的是 rs485 在 2 个 CRC 字节之后有一个额外的字节，其值为 FF。我找不到 2 之间的另一个区别。

以下是代码的相关部分：

设置端口

bool Serial::setup(){


    if(!openPort()){
        return false;
    }

    tcgetattr(fdPort, &options);

    cfsetispeed(&options, B115200);
    cfsetospeed(&options, B115200);

    options.c_cflag &= ~PARENB;

    options.c_cflag &= ~CSTOPB;
    options.c_cflag &= ~CSIZE;
    options.c_cflag |= CS8;

    options.c_cc[VMIN] = 0; 
    options.c_cc[VTIME] = 1;

    options.c_oflag &= ~(OCRNL | ONLCR | ONLRET |
                         ONOCR | OFILL | OLCUC | OPOST);

    options.c_iflag &= ~(IGNBRK | BRKINT | ICRNL | INLCR | 
                        PARMRK | INPCK | ISTRIP | IXON) ;

    options.c_lflag &= ~(ECHO | ECHONL | ICANON | IEXTEN | ISIG);

    if(tcsetattr(this->fdPort, TCSANOW, &options)){
        return false;
    }

    return true;

}

打开端口

bool Serial::openPort(){
    this->fdPort = open(this->port, O_RDWR | O_NOCTTY | O_NDELAY | O_NONBLOCK);

    if(fdPort == -1){
        return false;
    }
    else{
        //fcntl(fdPort, F_SETFL, 0);
        //fcntl(fdPort, F_SETFL, FNDELAY);
    }

    int status = 0;

    status |= TIOCM_RTS;
    ioctl(this->fdPort, TIOCMSET, &status);

    return true;

}

分块解释和读取数据的等待帧。

bool GlobalProtocol::WaitFrame(uint32_t timeOut) {

    int32_t bytesRec = 0;
    int32_t bytesToRec = 1;
    int recPhase = GC_PHASE_START;

    uint8_t *pData = m_RxBuff;
    bool commSuccess = true;

    m_LastError = boards::GCL_ERR_OK;

    while (readData(pData, bytesToRec, &bytesRec, timeOut)) {
        if (bytesRec) {
            switch (recPhase) {
            case GC_PHASE_START:
                if (*pData != GC_START_FRAME_BYTE) {
                    continue;
                }
                recPhase++;
                pData++;
                break;
            case GC_PHASE_DEST:
                if (*pData != m_MasterAddr) {
                    commSuccess = false;
                    break;
                }
                recPhase++;
                pData++;
                break;
            case GC_PHASE_SRC:
                recPhase++;
                pData++;
                break;
            case GC_PHASE_LEN_LO:
                if (*pData < 2 || *pData > GC_MAX_COMM_DATA_LEN) {
                    commSuccess = false;
                    break;
                }
                recPhase++;
                pData++;
                break;
            case GC_PHASE_LEN_HI:
                if (*pData != 0) {
                    commSuccess = false;
                    break;
                }
                recPhase++;
                pData++;
                bytesToRec = m_RxBuff[GC_PHASE_LEN_LO];
                break;
            case GC_PHASE_DATA:
                if (bytesRec != bytesToRec) {
                    commSuccess = false;
                    break;
                }
                recPhase++;
                pData += bytesRec;
                bytesToRec = 2;
                break;
            case GC_PHASE_CRC_LO:
                if (bytesRec != bytesToRec) {
                    commSuccess = false;
                    break;
                }
                if (CheckCRC(m_RxBuff, m_RxBuff[GC_PHASE_LEN_LO] + GC_PHASE_DATA + sizeof(uint16_t))) {
                    m_RecAddr = m_RxBuff[GC_PHASE_SRC];
                    return true;
                }
                commSuccess = false;
                break;
            }
            if (!commSuccess) break;
        }
        else break;
    }
    m_LastError = boards::GCL_ERR_ANSWERNOTREC;

    return false;
}

以及阅读的地点。

bool Serial::readData(uint8_t *data, uint32_t length, int32_t *receivedDataBytes, int32_t timeoutVal){
    int32_t tempReceivedDataBytes = -1;

    fd_set readFd;
    FD_ZERO(&readFd);
    FD_SET(fdPort, &readFd);
    struct timeval timeout;
    timeout.tv_sec = 0;
    timeout.tv_usec = timeoutVal * 1000;
    int test = 0; 
    uint32_t bytesAvail = 0;

    QTime timer;

    timer.start();

    if(fcntl(fdPort, F_GETFD) != -1){
        while(((test = select(this->fdPort + 1, &readFd, NULL, NULL, &timeout)) == 1) && (tempReceivedDataBytes == -1)){

            ioctl(fdPort, FIONREAD, &bytesAvail);

            if(FD_ISSET(fdPort, &readFd) && bytesAvail >= length){
                tempReceivedDataBytes = read(fdPort, data, length);
            }

            if(timer.elapsed() > (timeoutVal + 5)){ //fail-safe
                logger[debug_log] << "TIMEOUT" << endl;
                break;
            }

        }

        if(test == -1)
            logger[debug_log]<< strerror(errno) << endl;

        if(tempReceivedDataBytes < 0){
            return false;
        }
        if(tempReceivedDataBytes >= 0){
            *receivedDataBytes = tempReceivedDataBytes;
            return true;
        }

    }

    return false;
}

如果我将超时设置为 100 毫秒，那么它会等待 100 毫秒来读取 2 个字节，如果我将其设置为 10 毫秒，那么它会等待 10 毫秒来读取 2 个字节。

我尝试更改端口设置，但没有成功。

我已经尝试解决这个问题好几天了，但没有成功。

编辑： 我应该补充一点，ioctl(fdPort, FIONREAD, &bytesAvail); 将 bytesAvail 设置为 2，但 read 等到超时才能读取它们。

编辑 2：

这是一个超时设置为 25 秒的日志，以便您了解问题所在：

04/17/2014 15:51:50:584,Main board start:
04/17/2014 15:51:50:586,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:586,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:586,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:587,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:587,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:597,1 Received 110 Needed to receive 110
04/17/2014 15:51:50:597,1 Received 2 Needed to receive 2
04/17/2014 15:51:50:634,PID board start:
04/17/2014 15:51:50:635,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:635,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:635,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:635,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:635,1 Received 1 Needed to receive 1
04/17/2014 15:51:50:641,1 Received 70 Needed to receive 70
04/17/2014 15:52:15:647,0 Received 2 Needed to receive 2
04/17/2014 15:52:15:647,Set Leds board start:
04/17/2014 15:52:15:649,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:649,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:652,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:652,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:652,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:652,1 Received 2 Needed to receive 2
04/17/2014 15:52:15:652,1 Received 2 Needed to receive 2
04/17/2014 15:52:15:652,Get state board start:
04/17/2014 15:52:15:654,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:654,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:654,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:654,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:655,1 Received 1 Needed to receive 1
04/17/2014 15:52:15:657,1 Received 30 Needed to receive 30
04/17/2014 15:52:15:657,1 Received 2 Needed to receive 2

有问题的是 PID 板（在 rs232 上），其他都在相同的 rs485 上。

这里有一个超时设置为 30 毫秒左右（我不记得确切的值）：

04/17/2014 15:08:08:045,Main board start:
04/17/2014 15:08:08:046,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:046,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:046,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:047,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:047,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:056,1 Received 110 Needed to receive 110
04/17/2014 15:08:08:056,1 Received 2 Needed to receive 2
04/17/2014 15:08:08:078,PID board start:
04/17/2014 15:08:08:079,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:079,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:079,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:079,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:079,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:094,1 Received 70 Needed to receive 70
04/17/2014 15:08:08:120,0 Received 2 Needed to receive 2
04/17/2014 15:08:08:120,Set Leds board start:
04/17/2014 15:08:08:122,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:122,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:122,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:122,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:122,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:122,1 Received 2 Needed to receive 2
04/17/2014 15:08:08:122,1 Received 2 Needed to receive 2
04/17/2014 15:08:08:123,Get state board start:
04/17/2014 15:08:08:124,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:124,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:124,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:125,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:125,1 Received 1 Needed to receive 1
04/17/2014 15:08:08:128,1 Received 30 Needed to receive 30
04/17/2014 15:08:08:128,1 Received 2 Needed to receive 2

编辑：我仍然不知道出了什么问题。如果我删除 rs485 上的额外字节，它是相同的。这是另一个日志：

06/24/2014 12:57:01:923,Set Leds board start:
06/24/2014 12:57:06:701,Select value 1 Received: 1 Needed: 1 Bytes available: 9
06/24/2014 12:57:06:701,Select value 1 Received: 1 Needed: 1 Bytes available: 8
06/24/2014 12:57:06:702,Select value 1 Received: 1 Needed: 1 Bytes available: 7
06/24/2014 12:57:06:702,Select value 1 Received: 1 Needed: 1 Bytes available: 6
06/24/2014 12:57:06:702,Select value 1 Received: 1 Needed: 1 Bytes available: 5
06/24/2014 12:57:06:702,Select value 1 Received: 2 Needed: 2 Bytes available: 4
06/24/2014 12:57:06:752,Select value 0 Received: 2 Needed: 2 Bytes available: 2
06/24/2014 12:57:06:752,Get state board start:
06/24/2014 12:57:06:754,Select value 1 Received: 1 Needed: 1 Bytes available: 4
06/24/2014 12:57:06:754,Select value 1 Received: 1 Needed: 1 Bytes available: 3
06/24/2014 12:57:06:754,Select value 1 Received: 1 Needed: 1 Bytes available: 2
06/24/2014 12:57:06:754,Select value 1 Received: 1 Needed: 1 Bytes available: 1
06/24/2014 12:57:06:755,Select value 1 Received: 1 Needed: 1 Bytes available: 10
06/24/2014 12:57:06:758,Select value 1 Received: 30 Needed: 30 Bytes available: 30
06/24/2014 12:57:06:808,Select value 0 Received: 2 Needed: 2 Bytes available: 2
06/24/2014 12:57:06:886,Main board start:
06/24/2014 12:57:06:888,Select value 1 Received: 1 Needed: 1 Bytes available: 3
06/24/2014 12:57:06:888,Select value 1 Received: 1 Needed: 1 Bytes available: 2
06/24/2014 12:57:06:889,Select value 1 Received: 1 Needed: 1 Bytes available: 1
06/24/2014 12:57:06:890,Select value 1 Received: 1 Needed: 1 Bytes available: 23
06/24/2014 12:57:06:890,Select value 1 Received: 1 Needed: 1 Bytes available: 22
06/24/2014 12:57:06:898,Select value 1 Received: 110 Needed: 110 Bytes available: 113
06/24/2014 12:57:06:898,Select value 1 Received: 2 Needed: 2 Bytes available: 3

正如你所看到的，当可用字节数等于要读取的字节数时，它会在 read 函数中等待直到超时，然后返回。

【问题讨论】：

您可以使用硬件 RTS/CTS，但这意味着您的连接器必须针对它进行配置。或者，您可以使用 XON XOFF 来停止和启动数据。
问题不在于数据不存在，问题在于即使数据存在read 也会等到超时才读取。

标签： c++ linux serial-port serial-communication

【解决方案1】：

您使用的是什么硬件？真正的串口还是usb适配器？一些 FTDI usb 到串行适配器的配置使它们通过 usb 批量发送字节。这会在端口满载时加快传输速度，但在一次处理几个字节时它们的行为就像您提到的那样。

【讨论】：

在我的电脑上我有一个 USB 适配器，但在我正在为其制作应用程序的设备上我有一个真正的串行端口，问题是一样的。
我不认为由此引起的延迟真的会在超时的数量级，而是大约 1-2 毫秒...
根据我的经验，它是 >10 毫秒，但你是对的，100 毫秒对于这样的延迟来说可能太多了。

【解决方案2】：

我设法修复它。这是一个简单的修复。

我不得不替换while(((test = select(this->fdPort + 1, &readFd, NULL, NULL, &timeout)) == 1) && (tempReceivedDataBytes == -1)) 与 while( (tempReceivedDataBytes == -1) && ((test = select(this->fdPort + 1, &readFd, NULL, NULL, &timeout)) == 1)) .

如果串行缓冲区是空的，它会在select 中等待直到超时，即使它读取了一些内容。如果端口上有问题，它会检查第二部分并退出它。

【讨论】：

嗨，Alex，我遇到了类似的问题，我尝试搜索并遇到了您的帖子。我正在使用不同的硬件和软件（Altera Nios II 中的 C 代码将数据发送到串行端口，Matlab 访问串行端口并实时绘制图形）（在我阅读您的线程stackoverflow.com/questions/29122503/… 之前将我的线程发布在这里），请你告诉我一般算法你做了什么来解决这个问题，以便我可以在我的平台上进行必要的编码？请提前谢谢您

【解决方案3】：

设置一个非零的 VMIN 值，这样只要至少接收到这么多字符就可以满足读取。

这意味着：

如果没有缓冲数据，调用将等待某些数据超时
如果至少缓冲了 VMIN 个字符，调用将立即返回这些字符，而无需等待超时。

【讨论】：

我都试过VMIN设置为1和设置为0，问题是一样的。