Opening COM2

Opening COM2

[Bob Wilson]

I have a program which ran correctly when compiled on a gnu-win32
package from about a year ago, but is failing when compiled with 17.1
beta.  The machine is running NT 3.51 and COM2 is connected to a
microprocessor with only td, rd and ground connected.  The open:

        if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
            fprintf(stderr, "Cmd: Unable to open terminal\n");
            exit(1);
        }

hangs.  It doesn't help to tie the modem control lines high, but if I
generate a few characters on the rd line, the open completes.  In no
case is there an error return.

I have looked for this problem in the FAQ and looked for archives of
this mailing list, but both searches failed.

Can anyone help?

Thanks,
Bob Wilson
rwilson@cfa.harvard.edu
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Re: Opening COM2

[Jim Balter]

Bob Wilson wrote:
> 
> I have a program which ran correctly when compiled on a gnu-win32
> package from about a year ago, but is failing when compiled with 17.1
> beta.  The machine is running NT 3.51 and COM2 is connected to a
> microprocessor with only td, rd and ground connected.  The open:
> 
>         if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
>             fprintf(stderr, "Cmd: Unable to open terminal\n");
>             exit(1);
>         }
> 
> hangs.  It doesn't help to tie the modem control lines high, but if I
> generate a few characters on the rd line, the open completes.  In no
> case is there an error return.
> 
> I have looked for this problem in the FAQ and looked for archives of
> this mailing list, but both searches failed.
> 
> Can anyone help?

Marko Kohtala posted this patch to fix the problem the other day
(I haven't tried it and am not vouching for it):

diff -up b17.1/winsup/path.cc\~ b17.1/winsup/path.cc
--- b17.1/winsup/path.cc~       Wed Dec  4 05:23:01 1996
+++ b17.1/winsup/path.cc        Tue Apr  1 17:14:21 1997
@@ -1056,7 +1056,14 @@ symlink_check (const char *path, char *b
       char cookie_buf[sizeof (SYMLINK_COOKIE) - 1];
       DWORD done;
 
-      if (! ReadFile (h, cookie_buf, sizeof (cookie_buf), &done, 0))
+      if ((GetFileType (h) & ~FILE_TYPE_REMOVE) != FILE_TYPE_DISK)
+       {
+         /* It is not a disk file, can not be a symlink */
+         *syml = 0;
+         *exec = 0;
+         res = 0;
+       }
+      else if (! ReadFile (h, cookie_buf, sizeof (cookie_buf), &done,
0))
        {
          set_errno (EIO);
        }



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<J Q B>
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Re: Opening COM2

[Fergus Henderson]

Bob Wilson, you wrote:
> 
> I have a program which ran correctly when compiled on a gnu-win32
> package from about a year ago, but is failing when compiled with 17.1
> beta.  The machine is running NT 3.51 and COM2 is connected to a
> microprocessor with only td, rd and ground connected.  The open:
> 
>         if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
>             fprintf(stderr, "Cmd: Unable to open terminal\n");
>             exit(1);
>         }
> 
> hangs.  It doesn't help to tie the modem control lines high, but if I
> generate a few characters on the rd line, the open completes.  In no
> case is there an error return.

My guess is that this is due to the symbolic link handling.
When you open a file, cygwin will read the first few bytes
of the file to see if it has the special marker that is used
to indicate a symbolic link; if so, then cygwin will open the
file that the link points to.  Obviously this won't work
correctly in the case of device files such as `com2'...

-- 
Fergus Henderson <fjh@cs.mu.oz.au>   |  "I have always known that the pursuit
WWW: < http://www.cs.mu.oz.au/~fjh >   |  of excellence is a lethal habit"
PGP: finger fjh@128.250.37.3         |     -- the last words of T. S. Garp.
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Re: Opening COM2

[Geoffrey Noer]

Bob Wilson wrote:
> 
> I have a program which ran correctly when compiled on a gnu-win32
> package from about a year ago, but is failing when compiled with 17.1
> beta.  The machine is running NT 3.51 and COM2 is connected to a
> microprocessor with only td, rd and ground connected.  The open:
> 
>         if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
>             fprintf(stderr, "Cmd: Unable to open terminal\n");
>             exit(1);
>         }
> 
> hangs.

This should be fixed in beta 18.  I encountered similar problems trying to
talk to a serial port in a cygwin32-based gdb a little while ago.  The
solution was to rewrite some of the fhandler.cc code in the cygwin.dll
such that the classes make a little more sense.

The bottom line is that fhandler_base::open should not be checking
symlink/executable status of files, instead that code should be in
fhandler_disk_file::open which also does everything that
fhandler_base::open does.  Opening a com port is a fhandler_tty::open which
just defaults to the fhandler_base::open behavior.  This did the trick
for me.

-- 
Geoffrey Noer
noer@cygnus.com
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Re: Opening COM2

[David Fiddes]

> My guess is that this is due to the symbolic link handling.
> When you open a file, cygwin will read the first few bytes
> of the file to see if it has the special marker that is used
> to indicate a symbolic link; if so, then cygwin will open the
> file that the link points to.  Obviously this won't work
> correctly in the case of device files such as `com2'...
> 

Would this cause GDB to hang when trying to connect to a target "monitor"
on a development board. GDB seems to support(from it's list of targets and
the source) my monitor(dBUG for ColdFire) but it hangs when I type "target
dbug com2" (the default port settings for COM2 are OK). I haven't stuck a
terminal or a protocol analyser on it yet.....

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Opening COM2

[Markus Maeder]

Bob Wilson posted a message some time ago with some C source lines:

        if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
            fprintf(stderr, "Cmd: Unable to open terminal\n");
            exit(1);
        }

He stated, this doesnt function under b17. open hangs...

It seems, that this doesn't work under b18 either. Is there a patch?

Regards,
Markus



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Re: Opening COM2

[Gary Liddle]

the way to do it is
to 

fp = fopen("com2", "whatever");
comfd = fileno(fp);



> 
> Bob Wilson posted a message some time ago with some C source lines:
> 
>         if ((comfd = open("com2", O_RDWR | O_TEXT)) <= 0) {
>             fprintf(stderr, "Cmd: Unable to open terminal\n");
>             exit(1);
>         }
> 
> He stated, this doesnt function under b17. open hangs...
> 
> It seems, that this doesn't work under b18 either. Is there a patch?
> 
> Regards,
> Markus
> 
> 
> 
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> 
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Opening COM2

[Markus Maeder]

Sorry, it seems to work on another Computer.

I have to check configurations....

Bye,
Markus Maeder

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