MPC8548E w/ 4 Gig of DDR SDRAM

[Morrison, Tom]

Firstly, excuse my ignorance, I have looked at the archives to see 
if there was any mention of a subject like this - but I could NOT 
find a relevant one - so I ask forgiveness if I missed a thread 
discussing this - and/or if this is a real newbie question!
 
I have MPC8548E with 4 Gig of DDR SDRAM.

I am trying to figure out how to configure the MPC8548 & its 
Local Access Windows (and ?? what else) for 4 Gig of DDR SDRAM. 

I know traditionally, SDRAM starts at '0', and I believe that 
Linux is expecting some of the physical memory at this a low 
memory location?

So, I am in a dilemma - I don't want to waste some DDR RAM by 
also overlapping internal MPC8548 configuration registers 
that are located near the top of the lowest 4 GIG memory area...

So Can I:

 1) Split the definition for the DDR Local Access Windows into 2 pieces
     a) 2 GIG (starting at 0x0) 
     b) 2 Gig above (starting at 0x1_0000_0000)?

                   Or

2) Configure the LAW/MMU in a fashion before I load/boot Linux
    to use DDR at (a Local Access Window of) 0x1_0000_0000?

Thank you for your patience and suggestions on this subject.

Tom Morrison
Principal Software Engineer


EMPIRIX 
20 Crosby Drive - Bedford, MA  01730
p: 781.266.3567 f: 781.266.3670 
email: tmorrison at empirix.com 
www.empirix.com