Re: belkin usb serial converter (mct_u232), break not working
From: Paul Fulghum (paulkf_at_microgate.com)
Date: 10/21/04
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To: Thomas Stewart <thomas@stewarts.org.uk> Date: Wed, 20 Oct 2004 21:37:58 -0500
On Wed, 2004-10-20 at 18:04, Thomas Stewart wrote:
> porttest.c:
> #include <sys/fcntl.h>
> #include <sys/ioctl.h>
> main(int argc, char ** argv) {
> int r, fd = open(argv[1], O_RDWR|O_NOCTTY);
> r=ioctl(fd, TCSBRKP, 20);
> printf("%d\n", r);
> close(fd);
> }
>
> $ ./porttest /dev/ttyS0
> 0
> $ ./porttest /dev/ttyUSB0
> 0
OK, this is a kernel problem with send_break() in tty_io.c
Original:
static int send_break(struct tty_struct *tty, int duration)
{
set_current_state(TASK_INTERRUPTIBLE);
tty->driver->break_ctl(tty, -1);
if (!signal_pending(current))
schedule_timeout(duration);
tty->driver->break_ctl(tty, 0);
if (signal_pending(current))
return -EINTR;
return 0;
}
The USB serial driver break_ctl() sends a URB which does
a sleep and wakeup changing the task state back to TASK_RUNNING.
Because of this, schedule_timeout() above gets short circuited
and the break condition is not maintained long enough.
The normal serial driver break_ctl() leaves the task state
as TASK_INTERRUPTIBLE so you get the proper delay.
Thomas: try the patch below and let me know the results.
--
Paul Fulghum
paulkf@microgate.com
--- linux-2.6.8/drivers/char/tty_io.c 2004-08-14 00:37:15.000000000 -0500
+++ b/drivers/char/tty_io.c 2004-10-20 21:31:55.000000000 -0500
@@ -1703,11 +1703,11 @@ static int tiocsetd(struct tty_struct *t
static int send_break(struct tty_struct *tty, int duration)
{
- set_current_state(TASK_INTERRUPTIBLE);
-
tty->driver->break_ctl(tty, -1);
- if (!signal_pending(current))
+ if (!signal_pending(current)) {
+ set_current_state(TASK_INTERRUPTIBLE);
schedule_timeout(duration);
+ }
tty->driver->break_ctl(tty, 0);
if (signal_pending(current))
return -EINTR;
-
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- Previous message: Jeff Garzik: "Re: Linux v2.6.9... (compile stats)"
- In reply to: Thomas Stewart: "Re: belkin usb serial converter (mct_u232), break not working"
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