[U-Boot-Users] Re: [PATCH][CFT] bring ARM memory layout in line with the documented behaviour

[Wolfgang Denk <wd@denx.de>]

Dear Anders,

in message <fc.004c4e48001cba02004c4e48001cba02.1cba71@rea.de> you wrote:
> 
> here's a fairly lengthy patch against 0.4.8 that brings the memory
> layout of all supported ARM CPUs in line with the documentation.
> This has the positive side-effect of allowing U-Boot to actually run on
> PXA CPUs (the stock PXA implementation didn't set the start-address of
> the malloc pool at all!)
> 
> The memory layout now more or less conforms to the standard as defined
> in the README (the absolute addresses are board-specific, of course).
> 
> Since the stack and malloc-heap are now located below the U-Boot code,
> the TEXT_BASE of the supported ARM boards can be increased accordingly
> (for most (but not all) boards, the patch already does this).

This is actually the biggest "problem" with the existing ARM code (as
inherited from ARMBoot): with  the  orginal  philosophy  of  PPCBoot,
TEXT_BASE should not play ANY role here.

The way I would  like  to  soo  this  implemented,  and  as  it  _is_
implemented in PPCBoot (and in U-Boot for PowerPC) is as follows:

TEXT_BASE determines the start address in FLASH memory which is  used
before relocation.

The RAM initialization code is, among other  things,  responsible  to
determine  the  size  of  the RAM, and the relocation address is then
calculated DYNAMICALLY dependend on the RAM size found.  This  allows
that boards with different RAM sizes will always provide maximum free
RAM under U-Boot.


> Memory layout example based on my PXA255 (TEXT_BASE = 0xA07E0000):
> 
> 0xA079FF74   Monitor Stack (growing downwards)
> 0xA079FF80   Board Info Data and permanent copy of Global Data
> 0xA07A0000   Malloc Arena
> 0xA07E0000   RAM copy of Monitor Code
> ...          optional: Frame Buffer
> 0xA07FFFFF   [End of RAM]

I still see  references  to  _armboot_start,  _armboot_end_data,  and
_armboot_end - which role do these play now? Can we get rid of them?

How are they (should they be) set in your memory map above?

> Since I only have access to PXA-based HW, I was only able to verify
> that U-Boot still *builds* for all supported ARMs; I have to rely on
> your help to see if it also *runs* correctly.


I think some more code should  be  changed  like  the  allocation  of
display memory (see CONFIG_VFD in "lib_arm/board.c") - this should be
done like we do for PowerPC, too.


Any test results / comments from the other board maintainers?

Best regards,

Wolfgang Denk

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