[ECOS] Why virtual address and Physical address are different in the memory layout of IXPD425 board ?

[Sujoy Ray <raysujoy at yahoo dot com>]

Hello:

I was going through the memory laout of an IXPD425
board provided in the following link:-

http://sources.redhat.com/ecos/docs-latest/redboot/ixdp425.html


It has following lines.


Virtual Address   Physical Address  XCB  Description
0x00000000       0x00000000         010  SDRAM
(cached)
0x10000000       0x00000000         010  SDRAM (alias)
0x20000000       0x00000000        000 SDRAM
(uncached)

Now, I have following questions.

1. Why in the third line (SDRAM uncached), the virtual
address and physical address are different? I know
that virtual address can be different from the
physical address. But normally it is not in the
embedded scenario. 

2. Who is going to use this address? I have seen that
all the addresses are assigned in the .ld file and
those are static allocation. If this is true, then how
this virtual address will be used. 

May be 'am missing some fundamental concept. I would
be nice if anyone can help me in understanding this
concept in a better way.

Thanks in advance.

Regards,
Sujoy Ray.




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