[U-Boot] Getting started with uboot

[Wolfgang Denk]

Dear Thomas Heller,

In message <i3egu9$t2h$1 at dough.gmane.org> you wrote:
> 
> 'make uImage' in the linux kernel tree builds a linux kernel image
> that u-boot can use.  How can I change the compression that is used?

You can change these by changing the Make rules and/or providing
appropriate options.

> Actually, I'm not even sure whether my kernel is compressed or not.
> Here is the laat part of the output from 'make uImage'; it tells me
> the kernel is not compressed:

This not quite correct. It tells you that the payload it sees is not
compressed.

> however the embedded system tells me it is uncompressing:
> 
> > => bootm 0x80108000
> > ## Booting kernel from Legacy Image at 80108000 ...
> >    Image Name:   Linux-2.6.31
> >    Image Type:   ARM Linux Kernel Image (uncompressed)

That means: U-Boot does not know about any comprtession, so it does
not uncompress the payload.

> > Starting kernel ...

Here the kernel image started running...

> > Uncompressing Linux.................................................................................................... done, booting the kernel.

And this is doing the uncompressions.

This is a typical (wasteful) ARM image. On ARM, the kerne image gets
compressed - but instead of simply wrapping this into an uImage file,
they add their own uncompress code to it, which wraps the kernel
image, so what U-Boot sees is actually hte (uncompressed) wrapper code
which then does the copying / uncompressing.

If you say it makes littel sense to wste space for the images and time
for the loading for additional header code and uncompression routines
that are already ready avaialable in U-Boot I fully agree - but the
ARM kernel folks think different.

Best regards,

Wolfgang Denk

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