[U-Boot] more U-boot for Pentium

[Graeme Russ]

On Thu, Jun 30, 2011 at 11:54 AM, Raleigh Boulware
<r_boulware at hotmail.com> wrote:
>
>
>> 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.
>>
> So this is pnly used if we want to setup the SDRAM controller in C code

More that just that - It is used for the duration of board_init_f() which
may include all manner of peripheral initialisation prior to relocating
U-Boot into RAM.

> correct? In this code it is not used because the SDRAM cotroller is pretty
> much working from power up. So when I port this to my motherboard it looks
> as if i really do not need this.. Am I correct in this thinking??

You may need to initialise the SDRAM controller - It really depends on the
underlying hardware. You are going to need to have a good look at the
technical documentation for your board to figure this one out

Regards,

Graeme