my linux C program cannot receive data from Arduino through USB Serial

Question

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)

Answer 1

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

tcflush(fd, TCIOFLUSH);