Non Ovelapped Serial I/O

sunny_vc

HI all, I am working on Non Overlapped serial I/O application. I have only one thread to receive the data.For send i dont have any thread. I just call Write file when i need to send . My problem is, When I have my receive thread wait for an event using WaitCommEvent, it ties up the serial port. Then my sending function can't access the port with WriteFile. I knew waiting for a comm event would block the receiving thread but didn't expect that it would block use of the port. Any suggestions on how to do non-overlapped communication, where the send fucntion can write while the receive thread waits for a comm event?

Regards, Sunil Kumar

_Superman_

Try to open the port twice using CreateFile. Use one handle for writing and another for reading from the port.

«_Superman_» I love work. It gives me something to do between weekends.

sunny_vc

I dont think I can use CreateFile twice. It is unable to create the second time.The handle is getting some undefined value, when it is opened the second time.

Regards, Sunil Kumar

_Superman_

You should be able to open more than once if you specify the FILE_SHARE_READ and FILE_SHARE_WRITE flags.

«_Superman_» I love work. It gives me something to do between weekends.

CPallini

«_Superman_» wrote:

You should be able to open more than once if you specify the FILE_SHARE_READ and FILE_SHARE_WRITE flags.

You cannot do that with a communication resource (MSDN [^])

The CreateFile function can create a handle to a communications resource, such as the serial port COM1. For communications resources, the dwCreationDisposition parameter must be OPEN_EXISTING, the dwShareMode parameter must be zero (exclusive access), and the hTemplateFile parameter must be NULL. Read, write, or read/write access can be specified, and the handle can be opened for overlapped I/O.

:)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

sunny_vc

yeah, I am unable to open it twice even if I mention the shared attributes. There is no other option for non overlapped I/O, if I have to WriteFile, when my receive thread wait for an event using WaitCommEvent?

Regards, Sunil Kumar

CPallini

As workaround, you may use the same thread for both I/O. :)

If the Lord God Almighty had consulted me before embarking upon the Creation, I would have recommended something simpler. -- Alfonso the Wise, 13th Century King of Castile.
This is going on my arrogant assumptions. You may have a superb reason why I'm completely wrong. -- Iain Clarke
[My articles]

sunny_vc

Even If I have to send data in the same receive thread, I am unable to do as WaitCommEvent never returns. My code block is:

if (!SetCommMask( pc->hCommn, EV\_RXCHAR))
{
	//Error
}
for ( ; ; ) 
{
if (WaitCommEvent(pc->hCommn, &dwCommEvent, NULL)) 
{
  
	do
	{
	if (ReadFile(pc->hCommn, &chRead, 1, &dwRead, NULL))
	  {
		 // A byte has been read; process it.
		  pc->CopyRx(chRead);
	  }
	  else
	  {
		 // An error occurred in the ReadFile call.

		 break;
	  }
	}while(dwRead);
}

else
// Error in WaitCommEvent.
break;
}

Where can I call my send fucntion in this thread, if I have some data to send. Please suggest.

Regards, Sunil Kumar

_Superman_

I was wondering if DuplicateHandle[^] will work.

«_Superman_» I love work. It gives me something to do between weekends.

David Crow

Have you read this?

"Old age is like a bank account. You withdraw later in life what you have deposited along the way." - Unknown

"Fireproof doesn't mean the fire will never come. It means when the fire comes that you will be able to withstand it." - Michael Simmons

sunny_vc

Hi, I already read the article.But I am trying using Non overlapped I/O. If it is impossible to do using Non overlapped, i will shift to overlapped.

Regards, Sunil Kumar

Lost User

You cannot do that with a communication resource (MSDN [^])