[U-Boot-Users] Re: Patch s3c2410 nand-boot.

["David Müller (ELSOFT AG)"]

Hello

Gianluca wrote:
> I have changed NAND code only to remove warning beacuse I don't use
> some variable an then I rewrite "unsigned long nandptr = nand->IO_ADDR;" in
> "unsigned long nandptr;  nandptr = nand->IO_ADDR;".
>

Wolfgang and I have agreed, that direct hardware accesses and board
specific implementation details should be removed from "cmd_nand.c", but
should be implemented in a cpu and / or board specific low level NAND
flash driver instead.

Please take a look at the NAND part of the Linux MTD drivers to get an
idea how it should work.


> David, I've forwarded the patch to you. Can you please have a look at
> the implementation details? Thanks.
>

I'm afraid that "bulletproof" booting from a NAND flash is not as simple
as i may look at first. Please keep in mind that NAND flash are not 100%
error free, but contain an arbitrary number of "bad blocks" (and new
ones could appear during lifetime). Only the two first blocks of a NAND
flash device are normally guarantied to be error free. Additionally the
code which can be executed "directly" on the S3C24x0 when booting from a
NAND flash is further limited to 4KB in size.

So a multi stage boot process has to be implemented. After reset,
hardware loads a tiny piece of code from the first two blocks of the
NAND flash. This code has to do:

  - minimial initialisation of CPU
  - initialisation of SDRAM and NAND flash
  - copy rest of boot code (U-Boot) from NAND to SDRAM while taking
    care of bad blocks
  - jump to an appropriate place to give up control to rest of boot code



Dave