[U-Boot] more U-boot for Pentium

[Raleigh Boulware]

> Date: Thu, 30 Jun 2011 11:58:55 +1000
> Subject: Re: more U-boot for Pentium
> From: graeme.russ at gmail.com
> To: r_boulware at hotmail.com
> CC: u-boot at lists.denx.de
> 
> 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.
Is it possible to just set up the DDR controller early in the process in assembler to avoid doing a Cache as ram? The reason I ask is because I might have trouble getting other mother boards to do this.
 
Als I was looking at 2 rutines. board_init_r()  and board_init_f(). It appears that the code goes from assmbler to this board_init_f() then back to assembler then to board_init_r(). I am not sure of the reason for this.