rtems-boot-image tool: Raspberry Pi

[G. S. Niteesh]

On Wed, Feb 26, 2020 at 8:39 AM Chris Johns <chrisj at rtems.org> wrote:

> On 22/2/20 1:45 am, G. S. Niteesh wrote:
> > Hi,
> >
> > This is regarding adding RPi support to the boot image generation tool.
> >
> > The boot process for Raspberry Pi is very unconventional. The GPU starts
> > first, initializes RAM, other hardware, loads the bootloaders and then
> starts
> > the ARM CPU.
> >
> > The minimum files that are required to boot an RPi are
> > bootcode.bin, startx.elf, fixup.dat, kernel.img, config.txt
> > There are also other variants of startx.elf and fixup.dat.
> > Please have a look
> > at
> https://www.raspberrypi.org/documentation/configuration/config-txt/boot.md
> > for information on the variants.
> >
> > From what I have tried on my Rpi3 model b v1.2 the minimum files that are
> > required are start_x.elf, fixup_x.dat, bootcode.bin, kernel.img,
> config.txt
> > But for this to work, we must add start_x=1 to config.txt because by
> default
> > start.elf is loaded.

Hello Chris,


> I would have look at how the tool maps to RPi to know if it needs more
> work :)
>

Did you take a look at it?

In my opinion, there are two ways to do it.
The first would be to modify the U-Boot bootloader object to have a files
field
to make sure the user provides all the necessary files(fixup.dat,
startx.elf, config.txt).
So after this change the rtems-boot.ini for RPI should look something like
this
[u-boot-raspberrypi]
uses = u-boot-arm-raspberrypi
..
..
first_stage = %{ubootdir}/bootcode.bin
boot_device = mmc 0
second_stage = uboot or startx
files = [config.txt, fixup.dat etc]
But also please keep in mind that if we want to support RPi4 then the
first_stage
will start4x.elf since bootcode.bin is now replaced by code in the EEPROM
in RPi4 SOC.

Another approach will be to create the default Raspberry Pi bootloader
object. But having
support for U-Boot is important since it will allow for automatic testing.

Which one do you think is a better approach?

Thank you.

>
> >
> > So, what should be the values for the first and second stages in
> rtems-boot.ini
> > for Rpi?
>
> Would this be bootcode.bin?
>
> > And also wouldn't it be nice if we could add a files field, which will
> copy the
> > specified files to the image? This would save a lot of typing in case of
> RPi
>
> Do you have an example?
>
> Chris
>
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