[U-Boot] more U-boot for Pentium

[Graeme Russ]

Hi Raleigh,

On Thu, Jun 30, 2011 at 11:16 AM, Raleigh Boulware
<r_boulware at hotmail.com> wrote:
> I have been going through the code and I have stumbled accross a file called
> sc520_car.S that has something called Cache as ram. I am guessing that this
> is something special for the sc520 correct? Why was there a need to do this?
> Why was the Cache used like ram in the boot process?

Cache-As-RAM allows the CPU cache to be used as regular RAM while U-Boot
is running from Flash before the onboard SDRAM has been initialised. This
allows a temporary stack, and therefore C runtime environment to be
created. This this allows you to write the SDRAM initialisation code in C
which is a lot easier than assembler.

>
> Also I am I see something called early_board_init. I trace this to a file
> called eNET.S but all it does is jumps back to where it came from. I don't
> understand.

This is provided in case the board needs to do any specific initialisation
extremely early in the boot process. In the case of the eNET, no such
initialisation needs to be performed.

> Where is the external memory controller set up at?

For the sc520, the is no external memory controller, and the initialisation
of SDRAM is trivial (a couple of timing parameters in a control register)

> thanks for your time

Regards,

Graeme