Re: /dev/tty read is broken!

Re: /dev/tty read is broken!

[Steve O]

John E. A. Wrote:
> However if I run the program full speed, or step through the fgetc() on 
> cygwin without previously typing a character into minicom, then the fgetc()
> call hangs.

I'm not familiar with the winsup/cygwin/fhandler_serial code, but if I was
going to debug this (which sounds like fun, but I don't have the setup), 
I'd run:
  strace test > test.dump
and see what's happening right before the ^C, then I'd look at the
cygwin code mentioned above. 

-steve

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/dev/tty read is broken!

[John E. A.]

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fgetc(port) with port=/dev/ttyS0 hangs when no data is present.

I connect the serial ports of two PC's via a null modem. One running 
win2k/cygwin the other GNU/Linux.

To confirm that all h/w is working:
linux/minicom <-> win2k/hyperterm	- typing works both ways

Then two test configurations:
win2k/hyperterm <-> linux/test.c	- which works
linux/minicom <-> win2k/cygwin/test.c	- which fails as described below

With the following test program:

/*--------------------- test.c ---------------------*/

#include <stdio.h>

main ()
{
     FILE *port;
     unsigned int data = 'X';
     unsigned char *string = "Waiting for input...\r";

     port = fopen("/dev/ttyS0","w+");
     if (port == NULL) {
         perror("fopen");
         exit(1);
         }

     printf("Sending Prompt string:\n");
     fputs(string, port);
     fflush(port);

     printf("Now waiting for characters...\n");
     while (data != 'Q') {
         data = fgetc(port);
         printf("--->%c<---\n", data);
         fprintf(port, "--->%c<---\r", data);
         fflush(port);
         }

     /* close the serial port */
     fclose(port);
}

/*------------------ end of test.c ------------------*/

I step through this in gdb and it will step through the fgetc() call without 
error if a character has already been sent by the other end. However if I run 
the program full speed, or step through the fgetc() on cygwin without previously 
typing a character into minicom, then the fgetc() call hangs. I attached a text 
screen capture of this crash in gdb.

I also saw random hangs in either of the two fflush() calls that varied from 
build to build of test.c.

I have cygwin 1.3.18-1 on win2k.

I'm will try to help debug this if someone will offer guidance.

Will the /dev/tty guru (Mr. Steve O sir?) please HELP!!!

I'm desperate. This is my second post.

Thanks...

John E. A.

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johnea@BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$ make
rm -f  test.o
gcc -I.  -g -O -c test.c
gcc -g  -o test test.o

johnea@BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$ ./test.exe
Sending Prompt string:
Now waiting for characters...


johnea@BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$

johnea@BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$ gdb --nw test.exe
GNU gdb 2002-12-19-cvs (cygwin-special)
Copyright 2002 Free Software Foundation, Inc.
GDB is free software, covered by the GNU General Public License, and you are
welcome to change it and/or distribute copies of it under certain conditions.
Type "show copying" to see the conditions.
There is absolutely no warranty for GDB.  Type "show warranty" for details.
This GDB was configured as "i686-pc-cygwin"...
(gdb) break main
Breakpoint 1 at 0x401116: file test.c, line 9.
(gdb) r
Starting program: /cygdrive/c/Projects/testCygtty/test.exe

Breakpoint 1, main () at test.c:9
9           unsigned int data = 'X';
(gdb) n
12          port = fopen("/dev/ttyS0","w+");
(gdb)
13          if (port == NULL) {
(gdb)
18          printf("Sending Prompt string:\n");
(gdb)
Sending Prompt string:
20          fputs (string, port);
(gdb)
22          printf("Now waiting for characters...\n");
(gdb)
Now waiting for characters...
23          while (data != 'Q') {
(gdb)
24              data = fgetc(port);
(gdb)
[prompt does not return, Ctrl-C typed here -jea]

Program received signal SIGINT, Interrupt.
[Switching to thread 776.0x26c]
0x77ec7fb0 in _libkernel32_a_iname ()
(gdb) Quit
(gdb)