[U-Boot-Users] PXA (XScale) memory layout

[U-Boot-Users] PXA (XScale) memory layout

[Anders Larsen]

Hi folks,

is there any particular reason why the PXA uses a different memory
layout than the other ARMs?

It seems to be causing a certain amount of grief (and dirty workarounds,
like e.g. in board/wepep250/wepep250.c lines 43..53) that
cpu/pxa/start.S places stack (and heap) below the code instead of above.

I'd be grateful if somebody could enlighten me on this.

cheers
 Anders

[U-Boot-Users] PXA (XScale) memory layout

[Robert Schwebel]

On Thu, Sep 11, 2003 at 04:02:52PM +0200, Anders Larsen wrote:
> is there any particular reason why the PXA uses a different memory
> layout than the other ARMs?

The boards I have ported use the memory layout which is documented in
the README. Unfortunately, due to historical reasons the old ARMboot
code uses another scheme and nobody had the time to fix this "the right
way". 

> It seems to be causing a certain amount of grief (and dirty workarounds,
> like e.g. in board/wepep250/wepep250.c lines 43..53) that
> cpu/pxa/start.S places stack (and heap) below the code instead of above.

My -ptx patches have a hack for this, but I agree with Wolfgang that
somebody should fix it correctly instead of applying workarounds...

Robert
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
     Hornemannstra?e 12,  31137 Hildesheim, Germany
    Phone: +49-5121-28619-0 |  Fax: +49-5121-28619-4

[U-Boot-Users] PXA (XScale) memory layout

[Anders Larsen]

Robert Schwebel <robert@schwebel.de> schreibt:
>The boards I have ported use the memory layout which is documented in
>the README. Unfortunately, due to historical reasons the old ARMboot
>code uses another scheme and nobody had the time to fix this "the right
>way". 

Hi Robert,

even the relatively new (added sometime after 0.4.0) ARM925T code uses
the old scheme...

I fully agree, though, that the documented scheme is better (having the
stack grow downwards towards the code can lead to interesting side-
effects ;-)
>
>> It seems to be causing a certain amount of grief (and dirty workarounds,
>> like e.g. in board/wepep250/wepep250.c lines 43..53) that
>> cpu/pxa/start.S places stack (and heap) below the code instead of above.
>
>My -ptx patches have a hack for this, but I agree with Wolfgang that
>somebody should fix it correctly instead of applying workarounds...

AFAICT, cpu/pxa/cpu.c just needs to set

  _armboot_real_end = TEXT_BASE - CFG_MALLOC_LEN;

in cpu_init(), then no further "w?rgarounds" are needed for PXA boards.

After that, it's not too much work to fix the other ARMs, since the
entire magic plays in cpu/.../

Or did I miss something?

Cheers
 Anders

[U-Boot-Users] PXA (XScale) memory layout

[Wolfgang Denk]

In message <fc.004c4e48001c9311004c4e48001c9311.1c932e@rea.de> you wrote:
> 
> is there any particular reason why the PXA uses a different memory
> layout than the other ARMs?

It's just that the ARM port (which comes from  the  ARMBoot  project)
was  implemented differently than everything else. So far, nobody had
enough resources to clean this up.

> It seems to be causing a certain amount of grief (and dirty workarounds,
> like e.g. in board/wepep250/wepep250.c lines 43..53) that
> cpu/pxa/start.S places stack (and heap) below the code instead of above.

It is CORRECT to have stack and heap below the code.

> I'd be grateful if somebody could enlighten me on this.

It's just hysterical reasons - ARMBoot was implemented  that  way.  I
don't know why they broke the PPCBoot style.

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
"One thing they don't tell you about doing  experimental  physics  is
that sometimes you must work under adverse conditions... like a state
of sheer terror."                                    - W. K. Hartmann

[U-Boot-Users] PXA (XScale) memory layout

[Robert Schwebel]

On Thu, Sep 11, 2003 at 09:52:36PM +0200, Wolfgang Denk wrote:
> It is CORRECT to have stack and heap below the code.

The README has a nice chapter about how it _should_ be (and is in -ptx). 

> It's just hysterical reasons - ARMBoot was implemented  that  way.  I
> don't know why they broke the PPCBoot style.

s/hysterical/historical/ :-)

Robert 
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
     Hornemannstra?e 12,  31137 Hildesheim, Germany
    Phone: +49-5121-28619-0 |  Fax: +49-5121-28619-4

[U-Boot-Users] PXA (XScale) memory layout

[Wolfgang Denk]

In message <20030912051035.GX8367@pengutronix.de> you wrote:
>
> > It's just hysterical reasons - ARMBoot was implemented  that  way.  I
> > don't know why they broke the PPCBoot style.
> 
> s/hysterical/historical/ :-)

Oops. Seems my spelcheker is brocken ;-)

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
"A dirty mind is a joy forever."                       - Randy Kunkee

[U-Boot-Users] PXA (XScale) memory layout

[Anders Larsen]

Wolfgang Denk <wd@denx.de> schreibt:
>In message <fc.004c4e48001c9311004c4e48001c9311.1c932e@rea.de> you wrote:
>> It seems to be causing a certain amount of grief (and dirty workarounds,
>> like e.g. in board/wepep250/wepep250.c lines 43..53) that
>> cpu/pxa/start.S places stack (and heap) below the code instead of above.
>
>It is CORRECT to have stack and heap below the code.

I fully agree - only, the PXA implementation is incomplete; it places
the stack below the code and reserves space for the heap below the code
too, but it does not set the heap start address (which lib_arm/board.c
expects to find in _armboot_real_end), so U-Boot crashes when
start_armboot() calls mem_malloc_init(_armboot_real_end)!

board/wepep250/wepep250.c contains an incorrect workaround, which places
the heap above the code (leaving a huge hole below the code), the other
PXA boards cannot work as is (so they probably haven't been tested after
the code was copied from ARMboot).

BTW, the problem is partly documented with a FIXME comment in
cpu/pxa/cpu.c

As soon as I've figured out exactly how to initialize IRQ_STACK_START
and FIQ_STACK_START consistently, I'll submit a patch.

If you wish, I'd volunteer to fix the other ARM implementations, too
(but I only have access to PXA hardware for testing).

Cheers
 Anders

[U-Boot-Users] PXA (XScale) memory layout

[Robert Schwebel]

On Fri, Sep 12, 2003 at 10:02:36AM +0200, Anders Larsen wrote:
> If you wish, I'd volunteer to fix the other ARM implementations, too
> (but I only have access to PXA hardware for testing).

If you want to have access to a testbed tell me when you want to hack on
the code. I can setup a PXA machine in our Remote Lab. 

Robert
-- 
 Dipl.-Ing. Robert Schwebel | http://www.pengutronix.de
 Pengutronix - Linux Solutions for Science and Industry
   Handelsregister:  Amtsgericht Hildesheim, HRA 2686
     Hornemannstra?e 12,  31137 Hildesheim, Germany
    Phone: +49-5121-28619-0 |  Fax: +49-5121-28619-4

[U-Boot-Users] PXA (XScale) memory layout

[Wolfgang Denk]

Dear Anders,

in message <fc.004c4e48001c970e3b9aca00f6c2ed17.1c9734@rea.de> you wrote:
> 
> I fully agree - only, the PXA implementation is incomplete; it places
> the stack below the code and reserves space for the heap below the code
> too, but it does not set the heap start address (which lib_arm/board.c
> expects to find in _armboot_real_end), so U-Boot crashes when
> start_armboot() calls mem_malloc_init(_armboot_real_end)!

I know, but I don't have a PXA board here to  test  anything  myself.
Patches are welcome (they should try not to break the other ARM based
systems, though).

> As soon as I've figured out exactly how to initialize IRQ_STACK_START
> and FIQ_STACK_START consistently, I'll submit a patch.

Thanks n advance.

> If you wish, I'd volunteer to fix the other ARM implementations, too
> (but I only have access to PXA hardware for testing).

That would be excellent. I can test on some  ARM9  systems.  For  the
rest,  the  names and email addresses of the board maintainers are in
the MAINATINERS files.

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
A day without sunshine is like night.