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Old 02-09-2007, 10:42 AM   #1
glo
LQ Newbie
 
Registered: Jul 2003
Posts: 8

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Having trouble reading from serial port


Hi All,

I am very new to linux ( ~2 weeks old ) and I hope this is the right forum for my question.

I am trying to port some serial com port code over from Windows XP to Linux. Currently,
I am having trouble reading data from my serial port after writing some data to com port
I do a #cat /proc/tty/driver/serial to display COM port info after running my code.

serinfo:1.0 driver revision:
0: uart:16550A port:000003F8 irq:4 tx:114 rx:0 RTS|CTS|DTR
1: uart:unknown port:000002F8 irq:3
2: uart:unknown port:000003E8 irq:4
3: uart:unknown port:000002E8 irq:3

I assume tx:114 represents the number of bytes transmitted and rx:0 is the number of bytes received? Anyways, it looks like no data is coming back.

The setup is DTE-DCE where DCE is a data acquistion hardware connected to PCI slot on same computer and using serial com port for communication.

Questions:

1) Can someone show me the proper way to open serial com port for Linux Suse 10.1. I would like to elminate the possiblity that I have not opened and configured the serial port correctly. I've been playing around with the settings but no luck in fixing my problem.

2) I've enabled hardware flow-control. Should I be manually setting and un-setting the RTS/CTS signal using ioctl function in my code or should linux OS take care of that?

RTS/CTS signals:
[HTML]
DATA --[(DTE)QUERY DATA]--[(DCE)RESPONSE]--
________________
RTS __/ \___________________
___________________ ___
CTS \_______________/
[/HTML]

3) Does anyone know of any tools/tricks so I can check my COM port is working properly?


Any insight would be appreciated.

Thanks,

Geoff



My code (simplified):
Code:
main()
{
    BYTE inputCMD[7] = { 0x22, 0x23,0x34,0x33,0x02,0x62,0x03 };
    BYTE outputRES[10];
    MyCOM comport;

    if(comport.OpenPort())
    {
        comport.SendData(inputCMD,7)

        usleep(10000000);

        comport.ReceiveData(outputRES,10,&byteread);
    }
    else
    {
        printf("Unable to open port");
    }

}

bool MyCOM::OpenPort()
{
    
    //Open port
        m_fdComPort = open("/dev/ttyS0", O_RDWR | O_NOCTTY | O_NONBLOCK | O_NDELAY);
      
        // save current port settings 
    tcgetattr(m_fdComPort,&m_origtio); 
    
    BAUD  = B9600;
    DATABITS = CS8;
    STOPBITS = 1;
    PARITYON = 0;
    PARITY = 0;

    memset(&m_newtio,0,sizeof(m_newtio));
    cfsetispeed(&m_newtio,BAUD);
      cfsetospeed(&m_newtio,BAUD);

    fcntl(m_fdComPort,F_SETFL,FNDELAY);
    
    //Trying to configure character and parity settings for 8N1
    m_newtio.c_cflag &= ~PARENB;
    m_newtio.c_cflag &= ~CSTOPB;
    m_newtio.c_cflag &= ~CSIZE;
    m_newtio.c_cflag |=  DATABITS;       
    m_newtio.c_cflag |=  CRTSCTS;
    m_newtio.c_cflag |=  CLOCAL;
    m_newtio.c_cflag |=  CREAD;
    m_newtio.c_iflag = IGNPAR;
    m_newtio.c_iflag &= ~(BRKINT|ICRNL|INPCK|ISTRIP|IXON);
    m_newtio.c_oflag &= ~OPOST;
          m_newtio.c_lflag &= ~(ISIG|ECHO|ICANON|IEXTEN);     
          m_newtio.c_cc[VMIN]=1;
          m_newtio.c_cc[VTIME]=0;

    tcsetattr(m_fdComPort,TCSAFLUSH,&m_newtio);

    return true;
}

// Sends packet through communication port
bool MyCOM::SendData        
    (
    BYTE* packet,            //< The pointer to the packet to be transmitted 
    int nBytes            //< Size of packet (in bytes).
   &nbsp;)
{

    int bytesWritten = 0;    // number of bytes written to the firware
    bool success = false;    // CTS is not yet de-asserted yet
    unsigned long timeout = 0;
    bool bCTSStatus = false;
    
    // Should Wait until CTS gets asserted (up to 10 seconds)
    do
    {
        timeout++;
        bCTSStatus = GetCTS();
        if(bCTSStatus) break;
        
         if(TIMEOUT_LISTEN < timeout)
            printf("\nTIMEOUT waiting for CTS asserted\n");

        
    }
    while(timeout < TIMEOUT_LISTEN);
    
    if(bCTSStatus)
    {
    
        bytesWritten = write(m_fdComPort,packet,nBytes);
        if(0 < bytesWritten)
        {
            printf("\nBytes written = %d\n",bytesWritten);
            success = true;
        }
        else
        {
            printf("\nError writting bytes\n");
        }
    }
    else
    {
        printf("ERROR: CTS line is low - cannot send packet.");
        printf("       Check Connection to Power Manager.");
    }

    return success;
}


#define PRE_TIMEOUT 5000
#define POST_TIMEOUT 100

// Reads data through communication port
// NOTE: I copied the big while loop from some sample on line. Its suppose loop until I get some info back from serial port or timeout
bool MyCOM::ReceiveData    
    (BYTE* packet,    
    UINT16 expectedSize, 
    DWORD *nBytesRead)
{
    int iBytesRead=0;
    int iByteCtr=0;    

    int cnt =0;
    unsigned int offset=0;
    struct timespec tv;
    int timerflag =0;

    tv.tv_sec = 0;
    tv.tv_nsec = 100000; //100 ms
    
    while(1)
    {
        if(expectedSize < 1)
        {
            break;
        }

        //pre data timer
        if(!timerflag && 
            cnt >= PRE_TIMEOUT/(tv.tv_nsec/1000))
        {
            printf("\n!!!timeout while reading\n");
            break;
        }

        //post datatimer
        if(timerflag && cnt >= POST_TIMEOUT/(tv.tv_nsec/1000))
        {
            printf("\n!!!timeout while reading\n");
            break;
        }

        
        iBytesRead = read(m_fdComPort,packet+offset,1);
        if(0 < (int)iBytesRead)
        {
            iByteCtr += iBytesRead;
            timerflag = 1;
            cnt=0;
            --expectedSize;
            ++offset;
            continue;
        }
        else
        {
                    
        }
        ++cnt;
        nanosleep(&tv,NULL);
    }
*nBytesRead = (DWORD)iByteCtr;
return true;
}
 
  


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