HOW TO GDB USING COM PORT?

Hi,everyone.
I want to gdb my execuable using com port,and my target board is
s3c2410.
But there is some trouble in my way.
my buildfile is as follow:
[virtual=armle,binary]
bootstrap =
{
startup-integrator -v
PATH=/proc/boot procnto -vvv
}
[+script] .script =
{
procmgr_symlink …/…/proc/boot/libc.so.2 /usr/lib/ldqnx.so.2

Initialise the console

devc-serprimecell -e &
reopen
display_msg Welcome to Neutrino on the Integrator/AP Board
devc-pty &
pdebug /dev/ser1,115200 &
[+session] sh
}

Redirect console messages

[type=link] /dev/console=/dev/ser2
[type=link] /tmp=/dev/shmem

Shared libaries

libc.so

Executables

[data=c]
devc-serprimecell
sh=fesh
ls
pdebug
devc-pty
pidin
pipe
###END###

When i run pidin from the console,I know the pdebug is running
according the return message of the command.
Then i type “target qnx com1” and “info pid”,there
is nothing wrong from the ack message.
But when i type ‘run ls’, i have no message received, and after
several second the TimedOut appeared .
When i tring again,the connection is failed .

Is there anyone can tell me what to do?
Thanks.