The Nomadik 8815 CPU has a "secure" boot mode where no external access
(not even JTAG) is allowed. The "remap" bits in the evaluation board
are configured in order to boot from the internal ROM memory (in
secure mode).
The boot process as defined by the manufacturer executes external code
(loaded from NAND or OneNAND) that that disables such "security" in
order to run u-boot and later the kernel without constraints. Such
code is a proprietary initial boot loader, called "X-Loader" (in case
anyone wonders, it has no relations with other loaders with the same
name and there is no GPL code inside the ST X-Loader).
SDRAM configuration, PLL setup and initial loading from NAND is
implemented in the X-Loader, so U-Boot is already running in SDRAM
when control is handed over to it.
The Makefile offers two different configurations to be used if you
boot from Nand or OneNand.
make nhk8815_config
make nhk8815_onenand_config
Both support OneNand and Nand. Since U-Boot, running in RAM, can't know
where it was loaded from, the configurations differ in where the filesystem
is looked for by default.
On www.st.com/nomadik and on www.stnwireless.com there are documents,
summary data and white papers on Nomadik. The full datasheet for
STn8815 is not currently available on line but under specific request
to the local ST sales offices.
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