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Introduction to U Boot? /Lack of fundamental understanding

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I read a lot of U Boot documentation the last hours but I still fail at fundamental understanding, like:

- where can variables be set? boot.scr obviously, but there is also uEnv.txt boot.cmd armbianEnv.txt ... and in which order and precendence are they parsed? (If I set a variable in different files, which value will be used? first? last? ...)

- how is a change made persistent (saveenv does not work)

- Can sub-variables be changed, e.g. root in bootargs


what I am trying to achieve atm is to change the boot partion rootdev from p1 to p2. Even thou I think I patched the relevant files, printenv shows that bootargs and rootdev are still set to p1. Even if I set rootdev to ps (verified by printenv) running boot fails (and afterwards its set to p1 again).

I did not try to edit bootargs because I dont know how to do this without retyping the entire variable content (which is error-prone and annoying)



A lot of documentation is done on compiling/building, I basically want to now how to mange the "grub" part of u boot.

Would be nice if someone has a few hints or url(s) for me. Tahnk you.

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