[U-Boot-Users] My first embedded project

[Grant Likely <glikely@gmail.com>]

On Fri, 11 Feb 2005 14:57:39 +0100, Roger Larsson
<roger.larsson@norran.net> wrote:
> 
> Shouldn't it be possible to do this in two stages.
> 1) Have environment variables in flash/EEPROM so you can mount the CF disk
> 2) Run an autoscript(?) from that disk to change the variables (do not save)
> 3) Boot
> 
Would it be safe to assume that you're using a VIIPro w/ a SystemACE
boot device?  If so, is it also safe to assume that you want to do
this because your don't have a FLASH device?  Are you booting off of
BRAM that is loaded as part of the FPGA image?

If all of the above is true, another way to go about it is to use a
two stage boot loader system.  Create a very small boot loader that
lives in BRAM who's sole purpose in life is to load a more feature
rich bootloader off of the CF card from a predefined filename.  The
second stage boot loader can then also read boot parameters from CF
and provide a boot console.

If you wish to use u-boot, you could get a simple 1st stage to load
u-boot and it's environment image from CF into SDRAM.  u-boot then
becomes your second stage.

Wolfgang, regardless of the fact that the FAQ says that u-boot must
run out of FLASH, in this scenario it will be running out of SDRAM. 
Now, from what I know, I cannot see this being a problem because with
the VIIPro+SystemACE there is no SDRAM initialization that the
bootloader is responsible for.  Plus there is absolutely no FLASH
device available anyway.  Do you see this as a problem?  If so, what
are the likely issues that Roger may see?

Note; BRAM may be expensive so it is desirable to keep it as small as
possible; especially considering that the SystemACE loads the VIIPro
via JTAG.  Big Image=Slow Boot.  I would make the first stage loader
as dumb as possible.

At the risk of peeing in this particular pool; if there is still a
problem with running out of SDRAM then you may want to consider
RedBoot as your second stage.  Word of warning though; RedBoot/eCos
has a steep learning curve associated with it.

Cheers,
g.

> /RogerL
> 
> 
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