Creating serial port application

**tejendra** · 03-08-2011

I am creating a simple application in which i will open a serial port and configure it and make two threads one is reader thread and second is writer thread. writer thread will write on serial port and reader thread will read this data.
I have done with opening and configuring the serial port

now how a thread can write and read data from serial port; please help me out on this issue.

**~~CommonTater~~** · 03-08-2011

On what operating system?
On what hardware?

**tejendra** · 03-08-2011

the operating sytem is linux(ubuntu). kernel version 2.6.38-rc4.i am reading and writing on tty0 port.
i think hardware shouldn't matter.

**Mr.777** · 03-08-2011

Try reading this...

**tejendra** · 03-09-2011

Originally Posted by Mr.777

Try reading this...

i have done it already...now all i have to do is create two threads one is reader thread and another writer thread, reader will read data on serial port written by the writer; actually i am not getting the concept how a thread can write data.please give some example.

**Mr.777** · 03-09-2011

Try using

Code:

Log(char* s); // prints out a log message 
e.g.
Log("Thread writing...");
Output:Thread writing...

**Salem** · 03-09-2011

Erm, forget all about threads for the moment, and see how you get on with reading/writing the serial port using normal sequential code.

Threads are just a distraction until you can manage this simpler step.

**Mr.777** · 03-09-2011

First, you need to inherit your class from QThread class.
Then declare a pointer of type QTcpSocket...
And then use like..

Code:

Suppose,
class abc :public QThread{
private:
QTcpSocket * p;
public:
void write_Thread(QString writing_Data);
};
void abc::write_Thread(QString writing_Data){
p->write(writing_Data.toAscii());
}

**~~CommonTater~~** · 03-09-2011

Originally Posted by Salem

Erm, forget all about threads for the moment, and see how you get on with reading/writing the serial port using normal sequential code.

Threads are just a distraction until you can manage this simpler step.

I'm waiting till he discovers the output on a serial port is not connected to the inputs... You can't write "hello" then read it back... It won't be there.

He needs a "loopback" plug if he intends to send and recieve through the port on the same machine.

**tejendra** · 03-09-2011

My code look like this after opening and configuring the baud rates of the ports

Code:

#include<stdio.h>  // Standard Input/output definations 
#include<unistd.h> // UNIX standard function definations 
#include<fcntl.h>  // File control definations 
#include<termios.h>// POSIX terminal control definations 
#include<pthread.h>
int open_port(void)
{
 int fildes;//File descriptor
 fildes=open("/dev/tty0",O_RDWR | O_NOCTTY);
 if(fildes==-1)
 	printf("\nUnable to open port!\n");
 else
   {
 	fcntl(fildes,F_SETFL,0);//Manipulate file descriptor,F_SETFL will return the value of flag	
 	printf("\n**PORT IS OPEN**\n\n");
   }
}
int config_port(int fildes)
{
 struct termios termios_p;
 cfsetispeed(&termios_p,B38400);//Setting output baud rate
 cfsetospeed(&termios_p,B38400);//Setting input baud rate
 tcsetattr(fildes,TCSANOW,&termios_p);
 return (fildes);
 
}

int main()
{
int fildes=open_port();
config_port(fildes);

}

Actually i have to create this application with threads only.Without threads i know how to read and write directly on a serial port but after creating thread that thread should write i want the concept or code for this in which a thread read the data written by another thread.

**Mr.777** · 03-09-2011

Code:

int open_port(void)
{
int fildes;//File descriptor
fildes=open("/dev/tty0",O_RDWR | O_NOCTTY);
if(fildes==-1)
printf("\nUnable to open port!\n");
else
{
fcntl(fildes,F_SETFL,0);//Manipulate file descriptor,F_SETFL will return the value of flag 
printf("\n**PORT IS OPEN**\n\n");
}
}

Don't you really think, you should return some value that should be used by fildes in main()?

**tejendra** · 03-09-2011

Don't you really think, you should return some value that should be used by fildes in main()?

ya i will return it but this code is running,i will return the value once it is completed after writing code for creating threads and reading and writing data from serial port. Now please help me out i am in the middle of this application.

**Mr.777** · 03-09-2011

Didn't you read my above posts in which i told you to write with threads????
Try that and tell....

**tejendra** · 03-09-2011

Originally Posted by Mr.777

Try using

Code:

Log(char* s); // prints out a log message 
e.g.
Log("Thread writing...");
Output:Thread writing...

where have you created the thread and how will it read the tty0 port??

I think the more suitable approach will be creating a thread with posix library as pthread_create and in the start_routine we can give the read or write function which will read or write the serial port.Can we do it?

**Mr.777** · 03-09-2011

1
2

Code:

BOOL WriteABuffer(char * lpBuf, DWORD dwToWrite)
{
   OVERLAPPED osWrite = {0};
   DWORD dwWritten;
   DWORD dwRes;
   BOOL fRes;

   // Create this <strong class="highlight">write</strong> operation's OVERLAPPED structure's hEvent.
   osWrite.hEvent = CreateEvent(NULL, TRUE, FALSE, NULL);
   if (osWrite.hEvent == NULL)
      // error creating overlapped event handle
      return FALSE;

   // Issue <strong class="highlight">write</strong>.
   if (!WriteFile(hComm, lpBuf, dwToWrite, &dwWritten, &osWrite)) {
      if (GetLastError() != ERROR_IO_PENDING) { 
         // WriteFile failed, but isn't delayed. Report error and abort.
         fRes = FALSE;
      }
      else
         // <strong class="highlight">Write</strong> is pending.
         dwRes = WaitForSingleObject(osWrite.hEvent, INFINITE);
         switch(dwRes)
         {
            // OVERLAPPED structure's event has been signaled. 
            case WAIT_OBJECT_0:
                 if (!GetOverlappedResult(hComm, &osWrite, &dwWritten, FALSE))
                       fRes = FALSE;
                 else
                  // <strong class="highlight">Write</strong> operation completed successfully.
                  fRes = TRUE;
                 break;
            
            default:
                 // An error has occurred <strong class="highlight"><vb_highlight>in</strong></vb_highlight> WaitForSingleObject.
                 // This usually indicates a problem with the
                // OVERLAPPED structure's event handle.
                 fRes = FALSE;
                 break;
         }
      }
   }
   else
      // WriteFile completed immediately.
      fRes = TRUE;

   CloseHandle(osWrite.hEvent);
   return fRes;
}

The code above uses the WaitForSingleObject function with a time-out value of INFINITE, this causes the WaitForSingleObject function to wait for long until the operation is completed and this can make the thread appear to be "hung" when the write operation is simply taking a long time to complete or flow control has blocked the transmission.

Read the given links (1,2)

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