My linux c application cannot receive bytes from arduino

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My Linux C application cannot receive bytes from Arduino

Hi all, I intend to use Arduino Mega 2560 as a programmer for AT89S52 (a family of 8051 microprocessor). The Arduino board connects to PC via USB Serial cable.

At first I need to write a program in my Ubuntu to communicate with Arduino board. My program can open connection and write bytes to Arduino properly (I tested by turning led on/off), but the problem is that the Linux program cannot receive data from Arduino.
I already searched through many tutorials and forums but still cannot resolve the problem, so I post question here and hope that someone can help me.

- Below is my functon used to open connection to device

AT89S_EID
usbserial_open ( char* dev_name,
                 UsbSerialDevice* dev_ptr,
                 int baudrate,
                 int config )
{
    speed_t io_baudrate = B9600;

    if (dev_name == NULL || dev_ptr == NULL)
    {
        return AT89S_EID_ARG_NULL;
    }

    if (baudrate != US_BAUDRATE_9600
        || baudrate != US_BAUDRATE_19200
        || baudrate != US_BAUDRATE_115200)
    {
        return AT89S_EID_SERIAL_BAUDRATE_INVALID;
    }

    if (config != US_CONFIG_8N1
        || config != US_CONFIG_7E1
        || config != US_CONFIG_7O1)
    {
        return AT89S_EID_SERIAL_CONFIG_INVALID;
    }

    // store device name
    strcpy(dev_ptr->name, dev_name);

    // open device
    dev_ptr->fd = open (dev_ptr->name,
                        O_RDWR | O_NOCTTY | O_NDELAY | O_NONBLOCK);
    if (dev_ptr->fd < 0)
    {
        return AT89S_EID_SERIAL_OPEN;
    }

    // get current termios settings
    if (tcgetattr(dev_ptr->fd, &dev_ptr->tios) < 0)
    {
        return AT89S_EID_SERIAL_GET_ATTR;
    }

    // set input/output baudrdate
    if (baudrate == US_BAUDRATE_9600)
        io_baudrate = B9600;
    else if (baudrate == US_BAUDRATE_19200)
        io_baudrate = B19200;
    else if (baudrate == US_BAUDRATE_115200)
        io_baudrate = B115200;

    if (cfsetispeed(&dev_ptr->tios, io_baudrate) != 0
        || cfsetospeed(&dev_ptr->tios, io_baudrate) != 0)
    {
        return AT89S_EID_SERIAL_SET_IOSPEED;
    }

    // enable receiver, ignore status line
    dev_ptr->tios.c_cflag |= (CREAD | CLOCAL);
    // set config
    if (config == US_CONFIG_8N1)
    {
        dev_ptr->tios.c_cflag &= ~PARENB;
        dev_ptr->tios.c_cflag &= ~CSTOPB;
        dev_ptr->tios.c_cflag &= ~CSIZE;
        dev_ptr->tios.c_cflag |= CS8;
    }
    else if (config == US_CONFIG_7E1)
    {
        dev_ptr->tios.c_cflag |= PARENB;
        dev_ptr->tios.c_cflag &= ~PARODD;
        dev_ptr->tios.c_cflag &= ~CSTOPB;
        dev_ptr->tios.c_cflag &= ~CSIZE;
        dev_ptr->tios.c_cflag |= CS7;
    }
    else if (config == US_CONFIG_7O1)
    {
        dev_ptr->tios.c_cflag |= PARENB;
        dev_ptr->tios.c_cflag |= PARODD;
        dev_ptr->tios.c_cflag &= ~CSTOPB;
        dev_ptr->tios.c_cflag &= ~CSIZE;
        dev_ptr->tios.c_cflag |= CS7;
    }

    // no HW flow control
    dev_ptr->tios.c_cflag &= ~CRTSCTS;

    // no input processing (raw input)
    dev_ptr->tios.c_iflag &= ~(IXON | IXOFF | IXANY);
    // other input settings
    dev_ptr->tios.c_iflag &= ~(ICANON | ECHO | ECHOE | ISIG);

    // no output processing (raw output)
    dev_ptr->tios.c_oflag &= ~OPOST;

    // control character settings
    dev_ptr->tios.c_cc[VMIN]  = 1; // wait for 1 minimum chacacter received
    dev_ptr->tios.c_cc[VTIME] = 0; // no timeout when waiting for charater

    // commit new settings
    if (tcsetattr(dev_ptr->fd, TCSANOW, &dev_ptr->tios) < 0)
    {
        return AT89S_EID_SERIAL_SET_ATTR;
    }

    // wait for device reset & sync up
    usleep(1500 * 1000);

    return AT89S_EID_OK;
} /* usbserial_open */

- And this is the receiving function:

AT89S_EID
usbserial_recv ( UsbSerialDevice* dev_ptr,
                 unsigned char* data_ptr,
                 int data_len )
{
    int read_byte = 0;
    char b[1];

    if (dev_ptr == NULL
        || data_ptr == NULL)
    {
        return AT89S_EID_ARG_NULL;
    }

    // block reading
    fcntl(dev_ptr->fd, F_SETFL, 0);

    // start receiving data
    while (read_byte < data_len)
    {
        if (read(dev_ptr->fd, b, 1) > 0)
        {
            data_ptr[read_byte++] = *b;
        }
        else
        {
            if (errno == EAGAIN)
                continue;
            else if (errno == ETIMEDOUT)
                break;
            else
                return AT89S_EID_SERIAL_RECV;
        }
    }

    return AT89S_EID_OK;
} /* usbserial_recv */

So sorry for posting a long code :)

What I have tried:

I already searched through many tutorials and forums but still cannot resolve the problem. I believe that the Arduino code is working fine because I used some other tools to test it (e.g.: minicom)