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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 :)

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)

Huy Dang
  • 11
  • 4
  • You'll probably need to show the code that's using your functions here too. Also have you debugged your code ? What happens ? – nos Mar 04 '16 at 08:37
  • The problem is that I can send 256 bytes to arduino properly, but cannot receive full of 256bytes from arduino (I only received 1 byte). I used minicom to test my arduino code and can read & receive full of 256 bytes data. – Huy Dang Mar 05 '16 at 16:25
  • Right - but we can't tell what's wrong from this code - it looks fine. So you should run it in a debugger yourself and see what's going on (does it block in a read() call ? Does anything give you an error ? What happens after you received 1 byte ? etc. ). Or it's possible there's a bug in code that calls the functions you do have posted here. – nos Mar 05 '16 at 17:35
  • @nos: thanks for your suggestion. the read() call is blocking until it received byte then it return EAGAIN all the time. I think I will try to use some debugger now. I will post you back when I fix it :) – Huy Dang Mar 06 '16 at 03:08

1 Answers1

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I resolved my problem. Just add flush function when open the connection to device, everything can be working fine.

tcflush(fd, TCIOFLUSH);
Huy Dang
  • 11
  • 4