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Old 02-10-2009, 04:29 PM   #1
Registered: Feb 2009
Posts: 52

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Exclamation Well it worked in Windows..... Serial Port Communication Porting

I am working on a serial port communication project and porting over the code to run on linux from windows
Here is the Windows code that works properly(written in c#)
Porting it to c/c++

sp = new SerialPort(comPort);      
sp.BaudRate = 115200;  
sp.DataBits = 8;      
sp.Parity = Parity.None;
sp.StopBits = StopBits.One;
sp.DataReceived += new SerialDataReceivedEventHandler(sp_DataReceived);             
Here is my version on linux
int fd; /* File descriptor for the port */
//set baudrate
        tcgetattr(fd, &options);
        cfsetispeed(&options, B115200);
        cfsetospeed(&options, B115200);
        options.c_cflag |= (CLOCAL | CREAD);
        options.c_cflag &= !CSIZE;
        options.c_cflag |= CS8;
        options.c_cflag &= ~PARENB;
        options.c_cflag &= ~CSTOPB;
        options.c_cflag &= ~CSIZE;
        options.c_cflag |= CS8;
        tcsetattr(fd, TCSANOW, &options);
        fd = open("/dev/ttyS1", O_RDWR | O_NOCTTY | O_NDELAY);
if (fd != -1)
fcntl(fd, F_SETFL, 0);
fd returns 3 //assuming this is good, (the board has two serial ports, I try either ttys0 or ttys1 and get the same number)

Next its time to send a command to my board and see if it responds properly

Windows Version
     buffer[0] = 0x02;
            buffer[1] = 0x00;
            buffer[2] = 0x30;
            buffer[3] = 0x00;
            buffer[5] = 0x03;

            buffer[4] = (Byte)(buffer[0] ^ buffer[1] ^ buffer[2] ^ buffer[3] ^ buffer[5] ^ 0xEA);

            if (sp != null)
                if (sp.IsOpen)
                    sp.Write(buffer, 0, 6);
New Linux Version
 int8_t* buffer = new int8_t[6];
    buffer[0] = 0x02;
            buffer[1] = 0x00;
            buffer[2] = 0x30;
            buffer[3] = 0x00;
            buffer[5] = 0x03;

            buffer[4] = (int8_t)(buffer[0] ^ buffer[1] ^ buffer[2] ^ buffer[3] ^ buffer[5] ^ 0xEA);

    int returnval = write(fd, buffer,6);
    return returnval;
returns 6

I am suppose to see the hardware actually respond along with receiving a ACK/NAK back yet I get nothing out of the hardware nor do I receiving a ACK/NAK

My Receive in Linux
            int val2 = ReadTest(fd);
            if(val2 != 0)
              cout << val2;
int ReadTest(int fd)
    return fcntl(fd, F_SETFL, FNDELAY);
I receive a 0 from ReadTest always

This leads me to beleive that I am actually not opening the correct port or somethign along with opening the port is not correct.
Before i run the program I open the terminal and
//Allow me to use the ports
su -
chmod o+rw /dev/ttyS0
chmod o+rw /dev/ttyS1
//list of ports (if i remove card from the computer i only recieve line one, and not the "com" ports below", so I do KNOW that these are the correct ports to be interfacing with)
dmesg | grep tty
console [tty0] enabled
0000:02:00.0: ttyS0 at I/O 0xdf00 (irq = 21) is a 16550A
0000:02:00.0: ttyS1 at I/O 0xde00 (irq = 21) is a 16550A

Last edited by morty346; 02-10-2009 at 04:36 PM.
Old 02-10-2009, 04:56 PM   #2
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Try using stty (or copying its ioctls) to configure baudrate etc on your serial port.
Old 02-10-2009, 05:14 PM   #3
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int ReadTest(int fd)
    return fcntl(fd, F_SETFL, FNDELAY);
I don't think this actually reads anything. From man fcntl
Set the file status flags, defined in <fcntl.h>, for the file description associated with fildes from the corresponding bits in the third argument, arg, taken as type int. Bits corresponding to the file access mode and the file creation flags, as defined in <fcntl.h>, that are set in arg shall be ignored. If any bits in arg other than those mentioned here are changed by the application, the result is unspecified.
Upon successful completion, the value returned shall depend on cmd as follows:
Value other than -1.
So the 0 being returned from ReadTest means it succesfully sets the com port fd to no delay mode. I think you should use read.


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