Understanding U-Boot/Arch and Odroid C2 relationship

[Tshaw91]

Hello everybody,

My Odroid C2 is not booting when I try to flash it on a microSD card either an emmc. This is very surprising to me because I had it booting perfectly many times last years.

This year I tested Ubuntu Mate on the C2 and it successfully booted a lot of times on three different automatic configurations depending on how in bad state my file system was I think (either corrupt or 100/100 full)
Sometimes graphical, sometimes just terminal if graphical failed and sometimes just Busybox. This is how I discovered this thing.
I do not know exactly why this happens but I find it sometimes cool. A kind of "I don t know what will boot this time but I am sure that I am gonna have a shell to hack soon"

So now after these experiments and the fact that I want to go back on Arch (that I am not anymore able to boot like I said) I wonder what is U-Boot and if this can provide to me a kind of Basic Input Output System on my hardware with keyboard and HDMI support ?

Is that a good idea to flash U-Boot only on a SD card? Or this is completly useless due to the fact that U-Boot is just an invisible tool that make the kernel start and so will never have a shell, a debug interface or something basic to play with.

Thank you

[summers]

odroid c2 booting is tricky, because the the cpu has a secure boot. This means everything should be signed before booting. Strangely though the cpu will accept not secure signing - not that anyone does this ....

[Tshaw91]

Thank you for your answer. Do you know how I can have a minimalistic shell booting on C2 ?

[summers]

That depends on what you want to do, and how minimal. Do you want to access the shell via a uart or via ssh? My c2 I only access via ssh, havn't checked if it has graphics installed X/Weyland.

Anyway easy way is isntall arch linux, and remove bits you don't want: https://archlinuxarm.org/platforms/armv8/amlogic/odroid-c2.

If you want truly minimal, suggest looking at toybox http://landley.net/toybox/. Rob Landley is getting close to implementing a shell, which my guess is when it will move to version 1.0. Rob used to do linux as aboriginal linux, but now he uses mkroot, as part of toybox.

In toybox you'll almost certainly need uboot to get into the OS, so will need to work out how to sign. The uboot in arch is already signed, so works out of the box.

[Tshaw91]

I would like to try to access via ssh but in another topic for my specific problem of booting what you recommanded in October was to do it with uart.

"For you to find more of what is failing to work, you probably need to connect a serial interface to the main uart on the board. That would usually get the low level output during boot, and you can find out where it is failing ..."

How can I access an Odroid with UART? Do I need a USB-Uart adaptater and connect it to GPIOs?

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Thank you for your advice on "truly minimal" for Toybox. I see that you call it an OS too so maybe what I want to use on my DevBoard is not really ArchARM but just Toybox and this will "solve" my problem of booting Arch.

For flashing Toybox I think I need to learn how to build it, build U Boot and sign it. This is how I shouuld do this?