rtems-boot-image tool: Raspberry Pi

[Christian Mauderer]

Hello Niteesh,

thanks for the (private) remainder. This thread really stopped quite
some time ago. A lot of us are quite busy right now but that shouldn't
happen. If you don't get a response for some question: Please give it
about a week of time and then just ping the thread.

On 05/03/2020 11:06, G. S. Niteesh wrote:
> On Wed, Feb 26, 2020 at 8:39 AM Chris Johns <chrisj at rtems.org
> <mailto: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?

Chris is most likely too busy with the release right now.

> 
> 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.

As far as I understand that approach it more or less tells: To start a
raspberry you need U-Boot. U-Boot needs the fixup.dat, startx.elf and
config.txt to boot. But that sounds a bit wrong. On Raspberry U-Boot is
purely optional, isn't it? So from a high-level view it would be more a

- Raspberry needs fixup.dat, startx.elf and config.txt
- That can start either:
  - an application or
  - an U-Boot which can then start an application (or do other things)

> 
> 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.

That approach sounds more correct. But I don't really know the
rtems-boot-image tool. That makes it a lot harder for me to tell whether
that approach works well. From that ignorant position I would say that
it would be nice to have a boot-image command that can be called with or
without a option (like --with-u-boot). Alternatively maybe two targets
would be possible. One raspiboot-u-boot-pi1 and one raspiboot-raw-pi1.

But your best bet might is to wait for Chris to get free again and
answer that question. He knows the boot image tool and can tell you a
lot better which concept works best.

Best regards

Christian

> 
> 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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