Linux on PPC

Wolfgang Denk wd at
Sat Mar 4 13:09:38 EST 2006

In message <4408A1D3.8010506 at> you wrote:
> > Still not right. Even the physical memory is software settable. What
> > matters is what chip-select things are hooked up to, and then map those
> > chip selects correctly (size, base address, access with and so on)
> Thats what I meant with 'redefined in hardware'. But yes, redefined
> up to the limit of the wiring on the board of course (chip-selects
> and bus widths). That's where having the board schematic is
> invaluable.

You don't get it. You can map - for example - your flash to  physical
address  0x0000 or 0x04000000 or 0x40000000 or 0xFFF00000 as you like
- without any changes to the hardware, and  without  using  the  MMU.
Mind: that's all *physical* addresses.

> manual for the 440EP Yosemite board), and then setup U-Boot and
> Linux to program the TLBs to translate to those same addresses.

No. U-Boot does not use the MMU.

> when I booted Linux, I took a look and found that on the whole, Linux
> didn't touch too much of the things setup by U-Boot, i.e., the
> responsibility for setting up the Linux environment was mainly
> the job of the bootloader.

Wrong  again.  Linux  completely  re-initializes  the  whole   memory

> So, if I had a board with a custom bootloader, I would be
> concerned that the bootloader might not know enough about
> Linux, to setup the hardware correctly.
> Does that sound right?

No, it's wrong.

Best regards,

Wolfgang Denk

Software Engineering:  Embedded and Realtime Systems,  Embedded Linux
Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at
"Language shapes the way we think, and determines what we  can  think
about."                                                 - B. L. Whorf

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