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-----------------------------
NAND boot on PPC440 platforms
-----------------------------
This document describes the U-Boot NAND boot feature as it
is implemented for the AMCC Sequoia (PPC440EPx) board.
The PPC440EP(x)/GR(x) cpu's can boot directly from NAND FLASH,
completely without NOR FLASH. This can be done by using the NAND
boot feature of the 440 NAND flash controller (NDFC).
Here a short desciption of the different boot stages:
a) IPL (Initial Program Loader, integrated inside CPU)
------------------------------------------------------
Will load first 4k from NAND (SPL) into cache and execute it from there.
b) SPL (Secondary Program Loader)
---------------------------------
Will load special U-Boot version (NUB) from NAND and execute it. This SPL
has to fit into 4kByte. It sets up the CPU and configures the SDRAM
controller and the NAND controller so that the special U-Boot image can be
loaded from NAND to SDRAM.
This special image is build in the directory "nand_spl".
c) NUB (NAND U-Boot)
--------------------
This NAND U-Boot (NUB) is a special U-Boot version which can be started
from RAM. Therefore it mustn't (re-)configure the SDRAM controller.
On 440EPx the SPL is copied to internal SRAM before the NAND controller
is set up. While still running from cache, I experienced problems accessing
the NAND controller.
September 07 2006, Stefan Roese <sr@denx.de>
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