[U-Boot] u-boot serial loading/booting from ram

[Tom Rini]

On Thu, Aug 15, 2013 at 09:04:20AM -0400, Matt Geiman wrote:

> Hello all,
> 
> I have a quick question that I hope you can help me with.  We are running
> version 2009.11 of u-boot on a Beagleboard based project and are looking to
> upgrade to the latest and greatest (currently 2013.07).  This project has
> no MMC slot, so originally the only way to initially load the board for the
> first time was over a serial connection.  A previous employee wrote a piece
> of software (and customized x-loader) that would load x-loader, u-boot, the
> kernel, and a minimal filesystem into RAM.  It (the customized x-loader)
> would then boot the copy of u-boot in RAM, which would then flash
> everything to NAND.
> 
> So the process is:
> 
> 1. A script waits for the ASIC ID from the board and downloads our custom
> x-loader when it's received the ID.
> 2. The custom x-loader then can accept commands from our script to write
> the MLO, u-boot, kernel, and FS to RAM.
> 3. The custom x-loader then accepts a command to boot a certain area of
> memory, which is what starts u-boot.
> 
> Our problem is this; our piece of software and custom x-loader downloads
> the new u-boot file successfully, however when the custom x-loader tries to
> boot the new u-boot image from RAM it hangs/fails.  According to this:
> 
> http://www.denx.de/wiki/view/DULG/CanUBootBeConfiguredSuchThatItCanBeStartedInRAM

This page is correct, and a bit of a cop-out.  For a large number of
reasons, we don't want people chain loading U-Boot booting U-Boot
booting U-Boot ...

Of course, SPL is U-Boot, and boots U-Boot fine.  x-loader was U-Boot,
and boots U-Boot.  What's going on is that you need to take care when
starting U-Boot, just like SPL does.

-- 
Tom
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