[U-Boot] SteppingStone

[Cunsuo Guo]

2011/1/26 Albert ARIBAUD <albert.aribaud at free.fr>

> Le 26/01/2011 04:39, Cunsuo Guo a écrit :
> > 2011/1/26 Matt Johnson<mj1856 at hotmail.com>
> >
> >> Hello.
> >>
> >> I have a custom board with a Samsung s3c2410 (arm920t) processor.  I
> have
> >> been unable to get the main branch of u-boot to work with this board.
> >> However, I have been successful with the old OpenMoko fork.  (I believe
> it
> >> is because of the "SteppingStone" microcode. See
> >> http://wiki.openmoko.org/wiki/S3C2410_Steppingstone if you're
> unfamiliar.)
> >
> >
> >> I'd prefer to use the main branch, because the OpenMoko fork is old and
> >> unmaintained.  The OpenMoko project abandoned u-boot some time ago, in
> >> favor
> >> of their "Qi" bootloader.
> >>
> >> Has anyone looked at merging the SteppingStone code back in to the main
> >> branch?  Is there some other workaround that is unclear to me?
> >>
> >> Are there other bootloaders that support SteppingStone that I could try?
> >> I'm looking for something as full-featured as u-boot, but actively
> >> maintained. The only other that I've found is Vivi - which is super
> >> ancient.
> >> Any advice is appreciated.
> >
> >
> >> Thanks,
> >> Matt
> >>
> >> _______________________________________________
> >> U-Boot mailing list
> >> U-Boot at lists.denx.de
> >> http://lists.denx.de/mailman/listinfo/u-boot
> >>
> >
> >
> > Steppingstone is just a 4KBytes buffer which works together with some
> kinda
> > HW mechanism to copy the first 4KBytes of NAND to it. IMH, you can just
> > treat it as a feature provided by S3C2410 to support NAND boot. If you
> have
> > NOR flash in th board, you can simply boot from NOR flash and ignore this
> > feature.
> > I'm not sure whether there is some patches to support this feature or
> not,
> > if not, may be you could provide one. The following is my advice to
> > implement NAND boot for S3C2410:
> > 1. write your NAND device driver, simply read operation is OK;
> > 2. in the relocation part in  Start.S, read code from NAND to RAM use
> your
> > NAND device driver, and make sure the relocation part is in the very
> > beginning 4KBytes range of NAND (by Loader script). In this way, the
> > first 4KBytes in NAND will be read into Steppingstone buffer and
> executed,
> > after execution of relocation code, your bootloader code will be read
> into
> > RAM, and then the code can be executed in RAM, the full bootup procedure
> is
> > over.
>
> Why try to read from NAND to RAM in the relocation part of start.S,
> where you would not be able to use C or BSS variables?
>
> Because S3C2410 can _ONLY_ take the first 4KBytes into RAM (Basically some
hidden microcode in the S3C2410 takes care of copying the first 4KB of NAND
flash into RAM), so the rest code must be relocated into RAM from NAND by
the U-Boot code itself. Of course, there's no C environment set up yet, all
job should be done by assembly code.


> I thought the whole idea of the NAND SPL was to allow writing the
> NAND-to-RAM bootloader as a standalone "kind-of-U-boot", in C, with all
> the bells and whistles (that can fit in the NAND boot sector).


> Do I miss something?
>
> If not, then my opinion is that Matt should look into the NAND SPL code
> and fit it to initialize and use the stepping stone for initial SPL
> loading if he feels this is worth it.


> Amicalement,
> --
> Albert.
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