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Re: Problem with COM1 port from with GDB 5.3 under Cygwin 1.5.3-1
- From: Creighton MacDonnell <creighton at macdonnell dot ca>
- To: gdb at sources dot redhat dot com
- Cc: Thomas Doerfler <Thomas dot Doerfler at imd-systems dot de>
- Date: Wed, 10 Sep 2003 10:48:49 -0600
- Subject: Re: Problem with COM1 port from with GDB 5.3 under Cygwin 1.5.3-1
- References: <3F5F2C94.31945.291668BC@localhost> <3F5F5C7D.5659.2D0964@localhost>
As I mentioned in my first posting, the code in GDB for accessing
serial ports seems quite complicated. It does not just attempt to open
whatever you specifiy for a device name. There is code that builds up
some sort of "list of devices".
I expect this is to assist portability. But iin this case I think it is
doing the opposite. When I tried to use "/dev/ttyS0" as a device name
under the old Cygwin, GDB would say it "could not open the device". But
I think what may actually be happening is that "/dev/ttyS0" did not make
it into the list of devices.
I fear that GDB may be attempting to get a list of interfaces, or
information about interfaces, using some sort of lower level system
calls which Cygwin just stubs out. This might not only cause GDB to not
realize the device name is actually OK, but may cause it to attempt to
open COM? with inapproriate options.
If I were a Cygwin maintainer, and knew that GDB did not allow names
such as "/dev/ttyS0" under the old Cygwin, I might react that GDB should
be made "Cygwin-compatible" first. And after that, if there are still
problems with the "com?" names, they may want debug information that
could only be obtained by putting debug code into GDB.
In the end, it is we GDB under Cygwin users that have the problem. It
does not appear that many other Cygwin users care much about the serial
Thomas Doerfler wrote:
I just have passed some similar tests. I have connected a
Win32 terminal program to one COM port, and was trying to send
data to the other port using cygwin, with a loopback (null-
modem) cable attached.
$ echo bla >/dev/ttyS1
$ echo bla >COM2
and got the result on the serial line (and into my terminal
So at least sendig data from cygwin works fine.
Currently I don't know how to come around this. The problem
seems to be more connected to cygwin, because we see this with
at least two different gdb versions...