Debugging start_here: on IBM405GP

Hi all.
I'm using IBM405GP(not walnut, custom board) and linux-2.4.18-pre7 from BK Tree.
And I made bootloader myself and use it.

Attempting to debug, I can't see my debug character at "start_here:" (arch/ppc/kernel/head_4xx.S) and It seems to hang.
I have ported linux-2.4.2_hhl20 to my board and it now runs well.
But I don't know why new version of kernel doesn't work in my board.
Is anybody knows the reason?
Any help is greatly appreciated.

PS:
1) In my humble opinion, there are no board specific dependency before "start_here:".
So I think that any 405GP should runs well at "start_here:". Am I wrong?

2) is any dependency to processor revision? revision of my processor is E.


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