Beginners Questions about U-Boot

[markus2330]

Dear Community,

I could not find much information for beginners about the boot loader U-Boot as used in OLinuXino A20 (printenv says board_id=9604 board_name=A20-OlinuXino-LIME2-e16Gs16M board_revision=L). In particular I wanted to know the precedence of devices (I read somewhere SD is before internal MMC) and how to change command line arguments passed to Linux (I want to disable quiet to enable log output to HDMI, I only get a black screen with blinking cursor).

best regards,
Markus Raab

[JohnS]

Booting start with the silicon https://linux-sunxi.org/BROM

John

[markus2330]

Thank you, this is already super helpful, it clarifies the boot order.

But I still wonder about U-Boot. I found out that Olimex has its own u-boot-tools-olinuxino package, is there somewhere documentation about it?

For me not even basics work, e.g. when I boot up with a fresh A20-OLinuXino-bullseye-minimal-20220928-143706.img and run fw_printenv, I already get the error:

Code Select Expand

Read error on /uboot.env: Attempted to read 131072 bytes but got 8192
When calling savenenv during interrupting u-boot, the image gets in a reboot loop.

So how to change command line arguments for Linux? (e.g. disable quiet or use HDMI instead of serial tty etc.)

best regards,
Markus

[JohnS]

I'd just read up on uboot (& Linux e.g. startup / init command line)

John