TEXT_BASE question

Hi,

I am trying to install u-boot on my walnut board with PPC405. In file board/walnut405/config.mk, TEXT_BASE is defined as FFFE0000. Does that mean the u-boot.bin has to start from FFFE0000?

My problem is that on my board the address space from FFF80000 to FFFFFFFF is reserved for a special purpose, so I can't put the u-boot.bin at FFFE0000. But if I change the TEXT_BASE to another one, for example FFF00000, then the u-boot.bin generated by the compiler is FFFFFFFF - FFF00000 = 1MB. It means I still can't put the u-boot.bin to FFF00000 because it will overwrite the reserved address space anyway. I understand that u-boot is trying to fill the gap between TEXT_BASE and the end of the flash. So my question is:

1. If I use TEXT_BASE = FFFE0000 and simply put the u-boot.bin generated to FFF00000, will it mess up the addressing in the u-boot?

2. If the answer for 1 is yes, how can I move up the end of flash to FFF80000 so that the u-boot.bin will fill from FFF00000 to FFF80000 instead of from FFF00000 to FFFFFFFF?

Thanks,
Frank

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This is not possible. For example, the IBM 4xx processor hat it's reset vector at 0xFFFFFFFC, so the last 4 bytes in your address space cannot be "reserved for a special purpose" (except this "special purpose" is another boot loader).

Yes,. of course. Why do you think you have to ask this question? Isn't this obvious?

You cannot. At least a branch instruction must be paced at the reset vector, which is 0xFFFFFFFC, which is the end of your "reserved" area.

Please redefine your requirements.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-4596-87  Fax: (+49)-8142-4596-88  Email: wd at denx.de
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