Packet error when using kgdb

[yy Hong]

Hi all:
    I want to use kgdb debug kernel and driver on 8641d_hpcn. I refer to
Essential linux device drivers. I compile the kernel, open Magic SysRq key
and kgdb option in menuconfig.
But, when I use  ttyS0 connect to target board. I meet the error:

Ignoring packet error, continuing...
Ignoring packet error, continuing...
Ignoring packet error, continuing...
Malformed response to offset query, timeout
 Sometimes, I can connect to target board.But when I set breakpoint and step
to debug. I meet the same error above.
I use kernel v2.6.27.38.Toolchain is ELDK for ppc.
Is the kgdb tool  not stable？
I am a freeshman. Hope getting some suggestiong.
Thank you!
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