CODEWITHSUNDEEP
linuxserial-port
Dinesh
Dinesh

Reputation: 706

How to read from a Linux serial port

I am working on robot which has to control using wireless serial communication. The robot is running on a microcontroller (by burning a .hex file). I want to control it using my Linux (Ubuntu) PC. I am new to serial port programming. I am able to send the data, but I am not able to read data.

A few piece of code which is running over at the microcontroller:

Function to send data:

void TxData(unsigned char tx_data)
{
    SBUF = tx_data;  // Transmit data that is passed to this function
    while(TI == 0)   // Wait while data is being transmitted
        ;
}

I am sending data through an array of characters data_array[i]:

  for (i=4; i<=6; i++)
  {
      TxData(data_array[i]);
      RI = 0;              // Clear receive interrupt. Must be cleared by the user.
      TI = 0;        // Clear transmit interrupt. Must be cleared by the user.
  }

Now the piece of code from the C program running on Linux...

while (flag == 0) {
    int res = read(fd, buf, 255);
    buf[res] = 0; /* Set end of string, so we can printf */
    printf(":%s:%d\n", buf, res);
    if (buf[0] == '\0')
        flag = 1;
}

It prints out value of res = 0.

Actually I want to read data character-by-character to perform calculations and take further decision. Is there another way of doing this?

Note: Is there good study material (code) for serial port programming on Linux?

How can I read from the Linux serial port...

Upvotes: 0

Views: 3186

Answers (2)

ninjalj
ninjalj

Reputation: 43728

First, take a look at /proc/tty/driver/serial to see that everything is set up correctly (i.e., you see the signals you should see). Then, have a look at the manual page for termios(3), you may be interested in the VMIN and VTIME explanation.

Upvotes: 0

Amardeep AC9MF
Amardeep AC9MF

Reputation: 19054

This is a good guide: Serial Programming Guide for POSIX Operating Systems

The read call may return with no data and errno set to EAGAIN. You need to check the return value and loop around to read again if you're expecting data to arrive.

Upvotes: 3

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