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Re: Problem with COM1 port from with GDB 5.3 under Cygwin 1.5.3-1

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 port.

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.

I could

$ echo bla >/dev/ttyS1

and even

$ echo bla >COM2

and got the result on the serial line (and into my terminal screen)

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...


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