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What is the maximum physical RAM for a 32bit MIPS core?

To: linux-mips@oss.sgi.com
Subject: What is the maximum physical RAM for a 32bit MIPS core?
From: "Steven J. Hill" <sjhill@cotw.com>
Date: Tue, 05 Feb 2002 10:50:20 -0600
Reply-to: sjhill@cotw.com
Sender: owner-linux-mips@oss.sgi.com
I am just trying to fill in some more MIPS knowledge here. With a 32-bit
MIPS processor, we are forever limited to a userspace of 2GB in size thanks
to the kuser region. kseg0/1 map the same 512MB of physical memory. kseg2
is 1GB in size and hence it could address another 1GB of RAM. So, is the
maximum amount of RAM for a 32bit MIPS core:

   1) 1.5GB = 0.5GB kseg0/1 + 1.0GB kseg2

   2) 4.0GB = largest 32-bit address

   3) Something larger than 4.0GB by adding fancy external HW logic

Also, for choice #3, while it would be a hit in performance, could you use
the fp registers for 64-bit pointers to address larger than 4.0GB?

Thanks in advance.

-Steve
      
-- 
 Steven J. Hill - Embedded SW Engineer

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