How to enter to Uboot?

Jupiter
1

I have a standard image with

  • Bianbu 2.1
  • Linux kernel 6.6.63 #2.1.0.2 SMP PREEMPT Fri Jan 24 03:39:48 and
  • U-Boot 2022.10spacemit-gaebacc0c-dirty (Jan 24 2025 - 02:25:01 +0000

I try to enter to Uboot shell. I reboot my board but it doesn’t have any timeout and started to load a kernel immediately. It seems that bootdelay set to 0.

I’ve tried to get Uboot settings from Linux but couldn’t. fw_getenv doesn’t work.
Ho I can get to uboot shell?
Or is there only one way for me to build and flash my own uboot for this?

2

I don’t quite understand. Are you expecting U-Boot to behave like Grub or something?

3

Are you expecting U-Boot to behave like Grub or something?

Yes,
default Uboot behavior is booting, provide a chose to enter to uboot shell or boot a selected kernel

Current Uboot doesn’t have this delay to enter to uboot shell.
It seems I can rebuild Uboot and add this delay to default but maybe I have some other ways to enter to uboot shell?

4

Install u-boot-menu, and an extlinux folder will be added to /boot with the extlinux.conf configuration file, where you can change the values. For example, mine is set like this:
default l0
menu title U-Boot menu
prompt 1
timeout 10

5

In my case I don’t know why but u-boot-menu doesn’t effect a boot process.

But in anyway, I’ve found the answer.

To close he loop - Customize kernel boot params - #7 by Johnny_Test

Just rename a booted kernel file and it brake a boot process and you will be ejected to U-boot shell

6

I seem to remember that in the images where there was a dual boot of bianbu and buildroot, you had to hold down the Esc key to get the boot menu to appear.

7

Unfortunately, esc and ctrl+c don’t work.
This is the reason why I’ve asked.

8

I just remembered something. I had a similar problem with the kernel not working correctly when I added the following entries to the extlinux.conf file and tried to boot 6.6.77
label l0
menu label Bianbu 2.2.1 6.6.77
linux /vmlinuz-6.6.77
initrd /initrd.img-6.6.77

append root=UUID=\*\*\*\*\*\* rw default-hierarchy=legacy earlycon

label l1
menu label Bianbu 2.2.1 6.6.63
linux /vmlinuz-6.6.63
initrd /initrd.img-6.6.63

append root=UUID=\*\*\*\*\*\* ro earlycon

Of course, I would restart Jupiter, but I can’t reboot it; I’m waiting for the gcc-15.2.0*deb package build attempt to complete.

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9

Hold “s” while booting.

That should get you into the U-Boot console.

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