[U-Boot-Users] why jump at absolute address in start.S
Murray.Jensen at csiro.au
Fri Jan 3 14:48:50 CET 2003
On Fri, 03 Jan 2003 21:19:36 +0800, Laudney Ren <bren at sjtu.edu.cn> writes:
>I was very very very moved when I found you wrote such a detailed
>answer, providing so much background information, which would be
>precious to this list.
OK, thanks very much - it appears I didn't waste my time after all.
Just one thing ...
>When MPC8xx is reset, it starts to execute machine code at 0x100.
In fact, it might execute at 0xfff00100 or 0x00000100 depending on the
way your board designer has configured the hard reset (I think this is
correct for 8xx - I'm mainly 8260 these days and I have to think back).
That's the nice thing about this trick - it doesn't matter if it's
executing high or low at hard reset - we will relocate to the final
address that the flash is located at and it's all configurable.
>It's like a row of bricks which are the same. It makes no difference
>that which one you are standing on. Until the moment, in section
>_in_flash, we take away all the other bricks except one. If we haven't
>stood on the finally chosen brick, we'll fall. That's exactly what
>"disappear underneath" means.
Nice analogy :-) Cheers!
Murray Jensen, CSIRO Manufacturing & Infra. Tech. Phone: +61 3 9662 7763
Locked Bag No. 9, Preston, Vic, 3072, Australia. Fax: +61 3 9662 7853
Internet: Murray.Jensen at csiro.au
Hymod project: http://www.msa.cmst.csiro.au/projects/Hymod/
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