Mail Archives: cygwin/2012/05/25/05:38:42
On May 24 19:17, thunderboy42 wrote:
> Hello Corinna,
>
> I used a part from http://en.wikibooks.org/wiki/Serial_Programming/termios for
> testting because my 'original' is a little bit complicated. (see the source at
> the end)
>
> But I think I found the problem in "fhandler_serial.cc". There was some code
> added for leaving the method raw_read when there are no more chars received
> and the serial port was opened in non blocking mode (code starting at line
> 86). But I think it would be a good idea to deliver the chars received until
> then, so I build my own cygwin1.dll with the following changes in
> fhandler_serial.cc:
>
> 88,94c88
> - PurgeComm (get_handle (), PURGE_RXABORT);
> - if (tot == 0)
> - {
> - tot = -1;
> - set_errno (EAGAIN);
> - }
> - goto out;
> ---
> + break;
>
> This works for me now.
Thanks for the testcase and thanks for diving into the Cygwin source code.
I applied a slightly different patch. The problem is that, after calling
ReadFile, an overlapped operation is in progress. This overlapped I/O
must be stopped before leaving raw_read, so I changed the code after
ReadFile to cancel the I/O using the CancelIO function, rather than using
PurgeComm.
It's kind of weird, but in my testing, CancelIO just stopped the current
I/O without losing bytes, while calling PurgeComm (PURGE_RXABORT) would
result in lost bytes. That's a bit puzzeling. The description of
PurgeComm implies that PURGE_RXABORT only stops the I/O operation,
CancelIO-like. But apparently there's more going on in the device
driver when PURGE_RXABORT is called.
With the patch it works for me now without losing any bytes, even with
lots of data and with a bigger read buffer (1K instead of 1 byte).
Would you mind to test this a bit more intensive?
Thanks,
Corinna
--
Corinna Vinschen Please, send mails regarding Cygwin to
Cygwin Project Co-Leader cygwin AT cygwin DOT com
Red Hat
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