[U-Boot-Users] Re: U-boot for board bring-up

[Wolfgang Denk]

Dear John,

in message <C7FFFEA58B43D311920D0004ACE5333F10E4F5E0 at amer25.avnet.com> you wrote:
> 
> Bringing up a board is fraught with uncertainty -- I don't know if
> the fab house has the UARTs on right, if there are cold solder joints
> (or solder blobs) underneath a BGA, if the DRAM config is anywhere
> near correct, etc.  So for the very first software I put on a board,
> I am very very cautious.  In the past I've used our firmware for this
> purpose, since (a) it is very simple, and (b) I understand it inside
> out which is important when the hardware may be flaky.
> 
> Now, for our upcoming 440GX evaluation board, I'm considering putting
> U-boot on the board right from the start.  Reasons I'm uncertain
> about this are (a) U-boot is production-quality software, quite
> adequate for reliable hardware.  What are your experiences debugging
> it when the hardware *isn't* reliable?  (b) I'm not as familiar (yet)

U-Boot has been designed for board bring up. This is what we  do  all
the  time.  There  are  many  things  that  make the U-Boot code more
complicated on first glance, but help a lot  when  working  on  green
hartdware.

For example, many people have asked why we  run  such  a  complicated
init  sequence;  they suggested to wrtie a small assembler routine to
initialize RAM, copy U-boot to it, and only  then  start  the  "real"
code  -  the  reason I didn't implement it this was was that I always
want to have a serial console working as soon as possible, to be able
to see what's going  on.  RAM  initialization  is  one  of  the  most
difficult  issues  (in  the  sense  that  this  is  where most people
complain about problems), so  I  want  to  have  full  debug  support
including printf() available.

And so on.

I agree that you have to understand the code, ideally in and out, but
then you will see  that  U-Boot  is  pretty  well  suited  for  board
bringup.

> Reasons to go with U-boot are (a) it's known to work on another 440GX
> board, and (b) hopefully I shouldn't have to reinvent very much at
> all.

Both is correct.

> Do either of you have any thoughts?  If you were trying to run some
> code on a doubtful board, would U-boot be the first thing you would
> try to run?

For me: yea, without any second thought.

Best regards,

Wolfgang Denk

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