Thread: Wirte and read serial port

Originally Posted by Click_here

You are using "void main" - Have you seen Salem's avatar? Change it to "int main" and return 0 at the end.

Changed it already but still the output data i get sometimes correct and sometimes not correct. hmm.

The way i clear my buffer, is that a good way?

Where are you clearing your buffer? I'm not talking about your character buffer, I'm talking about the "hardware" buffer. You do know that both the operating system and the hardware usually buffer this port, right? To clear these buffers after you initialize the port you call tcflush().

Code:

tcflush(fd, TCIOFUSH); // Clear both the input and output buffers.

comment on my code below:

What's new to comment about? You haven't changed anything. You're still not checking if read() actually read anything. Please note this quote from this tutorial: Serial Programming Guide for Linux

Reading Data from the Port

Reading data from a port is a little trickier. When you operate the port in raw data mode, each read(2) system call will return the number of characters that are actually available in the serial input buffers. If no characters are available, the call will block (wait) until characters come in, an interval timer expires, or an error occurs. The read function can be made to return immediately by doing the following:

fcntl(fd, F_SETFL, FNDELAY);

The FNDELAY option causes the read function to return 0 if no characters are available on the port. To restore normal (blocking) behavior, call fcntl() without the FNDELAY option:

fcntl(fd, F_SETFL, 0);

Changed it already but still the output data i get sometimes correct and sometimes not correct. hmm.

What is this supposed to mean? You'll need to provide much more information. Does your external hardware have a method of outputting a predetermined string so you can check the communications? Can you tell us what type of hardware your trying to interface to? The manufacturer, and if the board is mass produced the model and part number of the device you're using?




Jim

Originally Posted by jimblumberg

Where are you clearing your buffer? I'm not talking about your character buffer, I'm talking about the "hardware" buffer. You do know that both the operating system and the hardware usually buffer this port, right? To clear these buffers after you initialize the port you call tcflush().

Code:

tcflush(fd, TCIOFUSH); // Clear both the input and output buffers.

What's new to comment about? You haven't changed anything. You're still not checking if read() actually read anything. Please note this quote from this tutorial: Serial Programming Guide for Linux




What is this supposed to mean? You'll need to provide much more information. Does your external hardware have a method of outputting a predetermined string so you can check the communications? Can you tell us what type of hardware your trying to interface to? The manufacturer, and if the board is mass produced the model and part number of the device you're using?




Jim

Hello jim, the problem seems to be solved already. I did the input and output clear buffer and its settled. Now i have another problem, below is my code to print the output from the device into a text file:

Code:

 fp = fopen("results_eigenvalue.txt", "w");   /*open and write into existing file*/

 for(i=0;i<207;i++)
{
 result = read(mainfd, &chout, sizeof(chout));          /* Read character from ABU (Auto buffering Unit) */
 if ( result == -1 ) { perror("error: read"); }
  if ( i >= 8){
    fprintf(fp,"%02x ",chout); }

}

Problem is the result i get is below:

f5 23 00 c4 00 00 e7 f5 f5 00 00 00 29 (for example)

What i need is some thing like below:

\xf5\x23\xc4\x00\x00\xe7\xf5\xf5\x00\x00\x00\x29

==> I tried to do this "fprintf(fp,"\x%02x ",chout);", but i get this error below:

error: \x used with no following hex digits

Any suggestion?