Re: mapping 36 bit physical addresses into 32 bit virtual

From: Maciej W. Rozycki (
Date: Wed Oct 16 2002 - 06:46:31 EST

On 15 Oct 2002, H. Peter Anvin wrote:

> Oh no, the x86 madness is spreading!!!!
> (It's depressing this happening on a MIPS system, which has been 64
> bits since who-knows-when...)

 Yep, but the reasons are different -- the embedded people are paranoid on
cutting away any possible bit of silicon and, admittedly, they are right,
to some extent. Why do they need 36-bit physical addressing in 32-bit
cores remains a mystery to me, though, yet the MIPS32 ISA spec permits up
to 36 bits (implementation-specific) here. Even more interesting is why
an implementation chose mapping of I/O devices there -- it's usually
easier for an OS to have them mapped within the low 29-bit address space
where they can be accessed bypassing the TLB.

+  Maciej W. Rozycki, Technical University of Gdansk, Poland   +
+        e-mail:, PGP key available        +

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