Mail Archives: cygwin/2003/01/10/05:17:51
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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 AT 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 AT BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$ ./test.exe
Sending Prompt string:
Now waiting for characters...
johnea AT BIGBOX-W2K /cygdrive/c/Projects/testCygtty
$
johnea AT 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)
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