barebox for a ti am335x based board

barebox for a ti am335x based board

[Giorgio Dal Molin]

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Hi all,

I'm trying to add board code for an am335x based HW project.
I had a look at similar boards like 'boards/phytec-som-am335x'
or 'boards/beaglebone'.
I understand that I need two images: the (little) MLO and the
(bigger) barebox.

What it's not really clear is how the MLO loads and starts the
barebox.

Moreover I saw there's always a call to:

 am33xx_save_bootinfo((void *)bootinfo);

in the MLO lowlevel entry function; I suspect the argument
'bootinfo' is the register r0 left by the function __barebox_arm_head()
but I cannot really understand the logic behind it.

giorgio


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Re: barebox for a ti am335x based board

[Alexander Shiyan]

>Среда, 14 февраля 2018, 1:13 +03:00 от Giorgio Dal Molin <giorgio.nicole@arcor.de>:
>
>Hi all,
>
>I'm trying to add board code for an am335x based HW project.
>I had a look at similar boards like 'boards/phytec-som-am335x'
>or 'boards/beaglebone'.
>I understand that I need two images: the (little) MLO and the
>(bigger) barebox.
>
>What it's not really clear is how the MLO loads and starts the
>barebox.
>
>Moreover I saw there's always a call to:
>
> am33xx_save_bootinfo((void *)bootinfo);
>
>in the MLO lowlevel entry function; I suspect the argument
>'bootinfo' is the register r0 left by the function __barebox_arm_head()
>but I cannot really understand the logic behind it.

Hello.
You can try to reuse my implementation AM335X code and change it
for your hardware.
https://github.com/shcgit/barebox-github/tree/am335x

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Re: barebox for a ti am335x based board

[Sascha Hauer]

Hi Giorgio,

On Tue, Feb 13, 2018 at 11:12:54PM +0100, Giorgio Dal Molin wrote:
> Hi all,
> 
> I'm trying to add board code for an am335x based HW project.
> I had a look at similar boards like 'boards/phytec-som-am335x'
> or 'boards/beaglebone'.
> I understand that I need two images: the (little) MLO and the
> (bigger) barebox.
> 
> What it's not really clear is how the MLO loads and starts the
> barebox.

See arch/arm/mach-omap/xload.c. It is compiled when no shell is enabled
(I think at least for clarity there should be a separate Kconfig
symbol). In this file omap_xload() detects where the SoC has booted from
and loads the full barebox from the same source.

> 
> Moreover I saw there's always a call to:
> 
>  am33xx_save_bootinfo((void *)bootinfo);
> 
> in the MLO lowlevel entry function; I suspect the argument
> 'bootinfo' is the register r0 left by the function __barebox_arm_head()
> but I cannot really understand the logic behind it.

When the am335x ROM passes control to the bootloader then it passes in
R0 a pointer to the bootinfo. This is a three word structure which has
informations where the SoC has booted from. In am33xx_save_bootinfo() we
copy the information to a known place where we can pick it up later, see
am33xx_bootsource().

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
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Re: barebox for a ti am335x based board

[Giorgio Dal Molin]

Hi,

thank you for the answer, meanwhile I also found the bootinfo
details in the ~5000 pages am335x datasheet.

Starting the second stage bootloader (barebox.bin file on the mmc)
from the MLO also works ('out of the box' actually).

giorgio

> On February 16, 2018 at 8:51 AM Sascha Hauer <s.hauer@pengutronix.de> wrote:
> 
> 
> Hi Giorgio,
> 
> On Tue, Feb 13, 2018 at 11:12:54PM +0100, Giorgio Dal Molin wrote:
> > Hi all,
> > 
> > I'm trying to add board code for an am335x based HW project.
> > I had a look at similar boards like 'boards/phytec-som-am335x'
> > or 'boards/beaglebone'.
> > I understand that I need two images: the (little) MLO and the
> > (bigger) barebox.
> > 
> > What it's not really clear is how the MLO loads and starts the
> > barebox.
> 
> See arch/arm/mach-omap/xload.c. It is compiled when no shell is enabled
> (I think at least for clarity there should be a separate Kconfig
> symbol). In this file omap_xload() detects where the SoC has booted from
> and loads the full barebox from the same source.
> 
> > 
> > Moreover I saw there's always a call to:
> > 
> >  am33xx_save_bootinfo((void *)bootinfo);
> > 
> > in the MLO lowlevel entry function; I suspect the argument
> > 'bootinfo' is the register r0 left by the function __barebox_arm_head()
> > but I cannot really understand the logic behind it.
> 
> When the am335x ROM passes control to the bootloader then it passes in
> R0 a pointer to the bootinfo. This is a three word structure which has
> informations where the SoC has booted from. In am33xx_save_bootinfo() we
> copy the information to a known place where we can pick it up later, see
> am33xx_bootsource().
> 
> Sascha
> 
> 
> -- 
> Pengutronix e.K.                           |                             |
> Industrial Linux Solutions                 | http://www.pengutronix.de/  |
> Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
> Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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Re: barebox for a ti am335x based board

[Sascha Hauer]

On Fri, Feb 16, 2018 at 10:15:37AM +0100, Giorgio Dal Molin wrote:
> Hi,
> 
> thank you for the answer, meanwhile I also found the bootinfo
> details in the ~5000 pages am335x datasheet.
> 
> Starting the second stage bootloader (barebox.bin file on the mmc)
> from the MLO also works ('out of the box' actually).

Nice ;) That's the way it should be.

Sascha


-- 
Pengutronix e.K.                           |                             |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |
Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0    |
Amtsgericht Hildesheim, HRA 2686           | Fax:   +49-5121-206917-5555 |

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